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Michigan State
University

 

This is to certify that the

thesis entitled
THE EFFECT OF LIGHT
ON PROLACTIN AND OTHER HORMONES
IN THE PREPUBERTAL BULL:
A PROSPECTIVE TOOL FOR HORMONE MANIPULATION
IN CATTLE
presented by

Kay B. Leining

has been accepted towards fulfillment
of the requirements for

Ph. D. . Dairy Science
degree in

 

 

Major professor

M 5,
Date ayl 1978

 

0-7639

 

THE EFFECT OF LIGHT
ON PROLACTIN AND OTHER HORMONES
IN THE PREPUBERTAL BULL:
A PROSPECTIVE TOOL FOR HORMONE MANIPULKTION .

IN CATTLE

BY

Kay B. Leining

A DISSERTNTION

Submitted to
Michigan State university
in partial fulfillment of the requirements
for the degree of

DOCTOR OF PHILOSOPHY

Department of Dairy Science

1978

(3/Vggdb;u;

ABSTRACT
THE EFFECT OF LIGHT
ON PROLACI‘IN AND OTHER HORMONES
IN THE PREPUBERTAL BULL:
A PROSPECTIVE‘TOOL FOR HORMONE MANIPULNTION
IN CNTTLE

By
Kay B. Leining

Prolactin (Prl), growth hormone (GH) and glucocorticoids have
been associated with growth and lactation in many mammalian species,
and environmental factors associated with changes of the seasons may
alter concentrations of these hormones.

Holstein bulls, 5 to 18 weeks of age and 52 to 150 kg body weight
at the beginning of experiments, were used to evaluate effects of dur—
ation (8. 16 or 20 hr daily), intensity (22 and 540 lux) and wavelength
(300 to #25 and 550 to 750 nu) of light on concentrations of Prl, CH,
glucocorticoids and other hormones in serum. Bulls were fed a complete
pelleted ration ad libitum and housed in groups of four in chambers
at 20 1:2 C and relative humidities of 60 to 69%. Blood was collected
twicedweekly by venipuncture at the midpoint of each photoperiod or
through cannulas at intervals before and after injections of thyro-
tropin releasing hormone (TRH; 33 ug/100 kg body weight).

Serum Prl concentrations averaged 8.1 ng/ml during exposure to
8L316D photoperiod but within 1 wk of 16L38D or 20Lt4D photoperiods
Prl increased 113%. and by the 8th wk serum Prl averaged 70.0 (16L18D)
and 55.0 (zoLsuD) ng/ml. Length of photoperiod did not affect concen-

trations of GB (8.3 to 11.7 ng/ml), but variations were less (p'< 0.01)

iwhen photoperiods were 8L316D (32 - 30.8) than when photoperiods were
_ 16Li8D or 20Li4D (s2 - 2h2.2). Concentrations of glucocorticoids
averaged 2.8 ng/ml after 6 wk of 8L316D photoperiods, then decreased
(p'< 0.05) to 1.“ ng/ml after 6 wk of exposure to 16L38D or 20Lr4D
photoperiods.

Concentrations of Prl increased 1.5-fold (p;; 0.05) in sera from
bulls which received 6 wk of 540 lux of light after initial exposure
to 22 lux (l6Ls8D photOperiods). In contrast, concentrations of Prl
in sera from bulls which received 6 wk of 540 lux followed by 6 wk of
22 lum did not change (hb.8 and 41.8 ng/ml). Variations of CH were
less (p1< 0.01) when light intensities were 22 lux (32 - 79.4) than at
540 lux (s2 - 321.8), although average concentrations of CH did not
differ (10.6 and 13.6 ng/ml). Concentrations of glucocorticoids and
Th did not differ in bulls exposed to 22 or 5&0 lux of light.

Concentrations of Prl increased (p'< 0.05) from 10.h ng/ml
' (8Li16D photoperiod) to 57.2 and 37.5 ng/ml within 5 wk after addition
of 8 hr. of 550-750 hill or 8 hr of 300425 nH light (16Li8D photoperiods).
Wavelength of light had no effect on concentrations of CH, glucocor-
ticoids, LH and T4, although number of episodic releases of GH and LH
etended to be greater during 16L38D than during 8L:16D photoperiods.

‘ Effects of duration, intensity and wavelength of light on
estimates of peak Prl and CH concentrations and area of the Prl and
CH response curves after injections of TRH were proportionate to
changes observed in serum samples collected by venipuncture. Duration,
intensity and.wawelength of light did not affect time required to

reach maxi-a1 concentrations of Prl and CH after injections of TRH,

nor subsequent disappearance rates (Ti) of Prl and CH. Similarly,
metabolic clearance rates and disappearance rates of Prl in bulls
infused with 0.50 mg NIH-B4 Prl per 100 kg BU did not differ after
6'wk of 8, 16 or 20 hr of light daily. EXposure of bulls to various
durations, intensities and wavelengths of light did not affect changes
in feed intake nor rate of increase in heartgirth.

Results from this series of experiments provide substantial

evidence that length and intensity but not wayelength of daily light

alters hormones associated with body growth and lactation in cattle.

DEDICNTION

”Great scientific revelations almost always stem from the fore-
going contributions of a host of workers. In endocrinology,
as in all other sciences, the person who fills in the final

. piece of the puzzle is declared the winner and receives more
credit than perhaps is due. It is virtually a necessity of
convenience that this is so. It is an accepted ground rule
.in scientific research and should be kept in mind when credit
for discovery is made in this or any other article. Such is
not peculiar to science for it is well known, history remem-
bers the generals of war but not the soldiers who fight and
die.”

Roy 0. Creep
"History of research on
anterior hypophysial hor-
mones” In Handbook of
Physiology Endocrinology
IV, Part 2.
I dedicate this thesis to Drs. James A. Koprowski and Raymond A.
_ Bourne, who completed the groundwork which stimulated my interest in

the effects of photoperiod on hormones, growth and lactation in cattle.

ii

ACKNOJLEDGHENTS

To acknowledge the many kind people who have helped me to com-
plete this dissertation would be impossible; so often the "help“ was a
friendly smile or a cheerful "good morning:”. To all of my contem-
poraries among the graduate students and staff, past and present, in
the miry Science department at MSU, I extend a sincere thank you.

I would like to express special appreciation to my committee
members, Dre. H. R. Bennink, ll. R. Dukelow, J. L. Gill and L. D.
McGilliard, for their advice and support.

Finally, I would like to thank Dr. Harold D. Hafs for challeng-
ing my spirit and my goals and Dr. H. Allen Tucker for challenging my

writing ability and my all-around ingenuity.

111

TABLE OF CONTENTS

LIST OF‘TABLES . . . . . . e .

LIST OF FIGURES . . . . . . .

INTRODUCTION . . . . . . . . .

REVIEH OF LITERATURE . . . e o

A. Environmental Regulation

1. Season . . .
2. Light . . .
3. Temperature
h. Circadian Rhythms
5. Feeding

Changes in Hormones Associated

Lactat ion

1 . mlaCt in e e e e
2. Growth Hormone . .
3. Glucocorticoids .

MATERIALS AND METHODS . . . e

A.
B.
C.
D.
E.

F.

RESUDTS

Experiment 1.

Aflimlseoeeeoe
Environmental Chambers

Blood Sampling Procedures

of Hormones

Hormone Assays e e e e e 0
Objectives and Experimental Design

Experiment 1 .
EXperiment 2.
Ebcperiment 3 .

Statistical Methods

0 O C O I O O O O O

with Growth

.Duration of Light .
Intensity of Light
Wavelength of Light

iv

Duration of Light . . .

Page
vi

viii

N

F‘PJ
O\FJVD\nto

18
22
27

31
31
31
32
33
36
36
39

#0

Experine
A.
B.
C.
D.

EXperime

DISCUSSION
SPECULNTIONS
SUMMARY AND
APPENDIX 0

BIBLIOGRAPHY

C. Thyrotropin . . .

Prolactin . . .
Growth Hormone

Other Hormones . .
Feed Intake and Body Growth
nt 2. Intensity of Light .
m18Ctineeeeeeeee
Growth Hormone . . . . . .
Other Hormones . . . . . .
Feed Intake and Body Growth
nt 3. Wavelength of Light
PmlaC‘Lin e e e 0
Growth Hormone .

Other Hormones . .
Feed Intake and Body Growth

CONCLIB IONS O O O O O O C 0

P888

53

56
59

61
61

70
7O

75

75
85

103
105

120

128
130

LIST OF TABLES

Table

1.

2.

3.

9..

10.

ll.

Radioiuunoassayseeeo.e...e...........

Dunnett analysis of prolactin (Prl) concentrations 4 to 18
days after increase of daily light from 8 to 16 or 20 hr .

Linear regression of log prolactin (Prl) concentration on
days after increase of daily light from 8 to 16 or 20 hr .

Prolactin (Prl) concentrations in serum collected by veni-
puncture or cannulation after daily eXposure of bulls to 8,
160r20hr0f118hteeeeeeeeeeeeeeeeeee

Prolactin (Prl) released to thyrotropin releasing hormone
(TRH) after daily exposure of bulls to 8 or 16 to 20 hr of

1 “ht I O O O O O O O O O O O O O O O O O O O C O O I O O 0

Rate of metabolic clearance of prolactin (Prl) after 6‘wk
or daily exposure of bulls to 8, 16 or 20 hr of light . . .

Growth hormone (GH) concentrations in serum collected by
venipuncture or cannulation after daily exposure to 8, 16
or 20 hr Of light 0 O O C C C C C . . O C C O C O O C C C .

Growth hormone (GH) released to thyrotropin releasing
hormone (TRH) after'daily exposure of bulls to 8 or 16 to
20hr°f118hteeeeeeeeeeeeeeeeeeeeee

Thyrotropin (TSH) released to thyrotropin releasing hormone
(TRH) after daily exposure of bulls to 8 or 16 to 20 hr of

lmt I O I O O O O O O O O O O O O O O O O O O O O O O O O

Insulin, glucocorticoid and thyroxine (Tu) in serum after
daily exposure of bulls to 8 or 16 to 20 hr of light . . .

Increase in 24 hr feed consumption and heartgirth measured
twiceaweekly during daily exposure of bulls to 8, 16 or 20
hrOflj-ghteeeeeeeeeeeeeeeeeeeeeeee

Prolactin (Prl) concentrations in serum collected by veni-

puncture or cannulation after daily exposure of bulls to
16 hr of 22 or 5b0 lux of light . . . . . . . . . . . . . .

vi

P889

35

a?

“7

#8

52

52

55

55

58

63

'Table

l3.
14.
15.

16.

17.
18.
19.
20.
21.
22.

23.

24,

Prolactin (Prl) released to thyrotropin releasing hormone
(TRH) after'daily'exposure of bulls to 16 hr of 22 or'540
In of light . . O C C C C C O C C C C C C C C C C C C C .

Growth hormone (GH) concentrations in serum collected by
venipuncture or cannulation after daily exposure of bulls
to 16 hr of 22 or 540 lux of light . . . . . . . . . . . .

Growth hormone (GH) released to thyrotropin releasing hor»
mone (TRH) after daily exposure of bulls to 16 hr of 22 or
9‘0 1‘“ Of light 0 O O O O O O O O D O O O O O O O O O O O

Glucocorticoid and thyroxine (Th) concentrations after
daily exposure of bulls to 16 hr of 22 or 540 lux of light

Increase in 24 hr feed consumption and heartgirth measured
twice-weekly during daily exposure of bulls to 16 hr of 22
or $0 1‘“ Of light 0 C C O C I O O O O O O O O C O O O O

Prolactin (Prl) concentrations in serum collected from bulls
by venipuncture or cannulation after 5 wk of daily exposure
to 8, 16 or 8 hr of various wavelengths of light . . . . .

Prolactin (Prl) released to thyrotropin releasing hormone
(TRH) after 5 wk of daily exposure of bulls to 8, 16 or 8
hr of various wavelengths of light . . . . . . . . . . . .

Growth hormone (GH) concentrations in serum collected from
bulls by venipuncture or cannulation after 5 wk of daily
exposure to 8, 16 or 8 hr of various wavelengths of light.

Growth hormone (GH) released to thyrotropin releasing
hormone (TRH) after 5 wk of daily exposure of bulls to 8,
16 or 8 hr of various wavelengths of light . . . . . . . .

Glueocorticoid and thyroxine (Tu) concentrations in serum
after 5 wk of daily exposure of bulls to 8, 16 or 8 hr of
VariouawavelonsthBOfJ-mhteeeeeeeeeeeeeee

Luteinising hormone (LH) concentrations in serum collected
through cannulas at 10 min intervals for 7 hr after 5 wk of
daily exposure of bulls to 8, 16 or 8 hr of various wave-.
1'.th Of light 0 C O O O C O O O O C C O O O O C C O O 0

Increase in 24 hr feed consumption and heartgirth measured

twice-weekly during 5 wk of daily exposure of two groups
of bulls to 8, 16 or 8 hr of various wavelengths of light.

vii

P888

67

71

72

74

79

89

95

97

98

104

LIST OF FIGURES

Figure

1.

2.

3.

5.

7.

Prolactin (Prl) in serum from prepubertal bulls during daily
light exposure which was increased from 8 to 16 hr (x-—x)
or from 8 to 20 hr (0---0). (four bulls per treatment) . .

Effect of weeks of exposure of bulls to 8le6D or 16L18D and
20Li4D photoperiods on prolactin (Prl) in serum after injec-
tion of thyrotropin releasing hormone (TRH). (eight bulls
per treatment) Standard errors of means for Prl collected
prior to TRH (-30 to 0 min) or at intervals immediately after
TRH corresponding to maximal concentrations (4 to 10 min) or'
disappearance of Prl (12 to 30 min), appear above response

CUNBSeeeeeeeeeeeeeeeeeeeeeeeeeee

Growth hormone (GH) in serum from prepubertal bulls during
daily light exposure which was increased from 8 to 16 hr
(x—-+x) or from 8 to 20 hr (0---0). (four bulls per treat-

1101110....-......................

Thyrotropin (TSH) in serum from prepubertal bulls during
daily light exposure which was increased from 8 to 16 hr
(x——<x) or from 8 to 20 hr (0---0). (four bulls per treat-

‘ ”Ont I I I I I I I I I I I I I I I I I I I I I I I I I I I

Prolactin (Prl) in serum from prepubertal bulls during
daily exposure to 16 hr of 22 (---) or 540 (-—) lux of

»1ight. (four bulls per intensity within each 6 wk interval)

Effect of intensity of light exposure on prolactin (Prl) in
serum after injection of thyrotropin releasing hormone (TRH)
in bulls exposed to 16 hr of light per day. (four bulls per
intensity within each 6 wk interval) . . . . . . . . . . .

Growth hormone (GH) in serum from pubertal bulls during
daily exposure to 16 hr of 22 (:f' or 540 (-——) lux of
light. (four bulls per intensity within each 6 wk interval

Effect of wavelength and number of hours of daily light

exposure on prolactin (Prl) in serum. (four bulls per
treatment ) I I I I I I I I I I I I I I I I I I I I I I I I

viii

P369

46

50 _

57

69

77

Figure_

9.

10.

l3.

l4.

15.

Effect of wavelength and number of hours of daily light
exposure on prolactin (Prl) concentrations in serum col-
lected at 30 min intervals for 7 hr on the last day of wk
5, 10 or 15. (four bulls per treatment) . . . . . . . . . .

Effect of wavelength and number of hours of daily light

exposure on prolactin (Prl) concentrations in serum collected
at 30 min intervals from bull 601 on the last day of wk 5, 10

or 15 I I I I I 'I I I I I I I I I I I I I I I I I I I I I I

Effect of wavelength and number of hours of daily light
exposure on growth hormone (GH) in serum. (four bulls per
tmatmnt) I I I I I I I I I I I I I I I I I I I I I I I I

Effect of wavelength and number of hours of daily light
exposure on growth hormone (GH) concentrations in serum col-
lected at 30 min intervals for 7 hr on the last day of wk 5,
10 or 15. (four bulls per treatment) . . . . . . ... . . .

Effect of wavelength and number of hours of daily light
exposure on growth hormone (GH) concentrations in serum
collected at 30 min intervals from bull 601 on the last day

.OfWkSIIOOIISIIIIIIIIIIIIIIIIIIIII

Luteinizing hormone (LH) concentrations in serum collected

_from bull 596 on the last day after 5 wk.of daily exposure

to 8. 16 or 8 hr at light 0 e e e e e e e e e e e e e e e e

Luteinizing hormone (LH) concentrations in serum collected
from bull 599 on the last day after 5 wk of daily exposure
to 8. 16 or 8 hr Of light 0 e e e e e e e e e e e e e e e o

Page

81

83

87

91.

100

102

INTRODUCTION

The hormones prolactin (Prl), growth hormone (GH) and gluco-
corticoids have been associated with growth and lactation in many
mammalian species. Dutt (1960). Ortavant et a1. (1961;). Ortavant (1977).
Meier (1972) and Ringer (1977) suggested that environmental factors
associated with seasonal changes alter the relative concentrations of
hormones. These reviewers also claimed that environmental factors
associated with seasonal changes influence growth and lactation in farm
animals.‘ Thus, the question becomes: do changes in season affect
hormones which in turn affect growth and lactation?

The objective of research reported in this dissertation was to
examine effects of one major component of season, light, on secretion
of Prl, CH and glucocorticoids. This research was based on the obser-
vations of Bourne and Tucker (1975) that changes in concentrations of
Prl in blood serum in bull calves paralleled changes in hours of daily
exposure to light. Experiments were designed to determine if duration,
intensity or wavelength of light affected serum Prl. Also, the effects
of light on the relationships among serum Prl, CH and glucocorticoids
were determined. In certain experiments concentrations of insulin,
luteinizing hormone (LH), thyrotropin (TSH) and thyroxine (T4) were
quantified. The possibility that light can be used to manipulate hor—

mones, growth and lactational traits in cattle is considered.

REVIEH OF LITERATURE

Ahg_fimwironment§1 Regulation of Hormones
In natural habitats, systems have evolved that allow mammals
to sense regular changes in their environment. Environmental cues
initiate reproductive processes which ensure that offspring are born
during conditions which favor survival. Hormones mediate the response
of animals to exteroceptive stimuli (Farner and Follett, 1966;
Henaker, 1971).

7 Environmental cues to be discussed include effects of season,
and two components of season, light and temperature. Research which
suggests that some hormones vary with periodicity will be reviewed.
Since food intake affects hormones, this topic also will be discussed.
These factors probably alter hormone concentrations through nervous
stimulation of hormones secreted by neurons in the basal hypothalamus.
These neurohormones, in turn, modify the anterior pituitary's ability
to synthesise or release its hormones (Convey, 1973)-

1! Season

In 1973, Pelletier reported that season affected hormone concen-
trations in addition to reproductive traits in the sheep and that the
photoperiod component of season was the primary cue. When Pelletier
provided rams with 6 no light cycles which mimicked seasonal changes
in hours of exposure to light, Prl concentrations in serum were great-
est when photoperiod first reached 16 hr and least when photoperiod

2

. wasat its nadir of 8 hr.

In rams, spermatogenic activity of the testes (Ortavant and
Thibault, 1956) and LH concentrations in serum (Pelletier and Ortavant,
1975a) rapddly increased when daily photOperiod initially decreased
from 16 hr. Neither castration nor injections of testosterone propio-
nate affected the cyclical changes in Prl and LR associated with
changing light cycles: which supports the hypothesis that photoperiod
is the primary regulator of the seasonal changes of Prl and LH
(Pelletier and Ortavant, 1975a, b).

Although reports imply that cattle also exhibit seasonal vari-
ation in milk production (Touchberry, 1974; Mac et al., 1974), milk
components (Head et al., 1976). reproduction and fertility (Dutt, 1960; ‘
Ortavant et al., 1961) and feeding behavior (Stricklin et al.,_ 1976),
researchers have only recently obtained evidence that season may alter
hormones associated with these production traits.

In 1972 Schams reported that stimuli associated with milking
released Prl into the blood of dairy cows. His conclusion that season
may influence magnitude of milking-induced release of Prl was tentative
because comparisons between seasons were confounded with variation of
individual animals and stages of lactation. Kaprowski and Tucker (1973)
, supported both of Schams' claims. Concentrations of Prl in serum from
55 cows bled from wk 4 through 44 of lactation were greater between
April and September (74 ng/ml) than during the remainder of the year
(35 ng/ml). Release of Prl during milking decreased as lactation
advanced. In addition, when data were adjusted for stage of lactation,

release of Prl at milking was less during summer (19 ng/ml) than.during

winter (33 ne/nl).

Serum Prl concentrations in bulls increased 10-fold or more
between winter and summer, adding variance which decreased repeat-
abilities of the trait (Tucker et al., 1974). Even repeatability of
basal Prl on the same bull within 10 days was small (r - 0.13).

Calves born in May or June tended to have greater Prl concen-
trations at birth than calves born between October and Nevember
(Schams and Reinhardt, 1971.). In addition, hours of daylight and
ambient temperatures were correlated (r'- 0.90) with Prl concentrations
measured from birth to maturity in cattle. Values for Prl in serum
were greatest during Hay through August and decreased significantly
between October through January.

Seasonal influence on Prl concentrations in domestic animals
is not limited to the cow, because yearly rhythmic changes in Prl
concentrations in goats were correlated with hours of daylight (r -0.8)
and mean temperature (r'- 0.5). In lactating goats, Hart (1975)
observed a gradual decrease from August through December in milking-
induced Prl surge and milk yield. Concentrations of Prl released
during milking were maintained if goats were exposed to artificial
light for 17 hr daily from August through December, yet milk yield
still decreased as lactation advanced.

Circannual cycles (of or about a year) in concentrations of Prl
in serum were not noted in men or monkeys (Gala at al., 1977): rather,
alterations of Prl in each individual followed cycles of 4 to 50 wk.

Season did not affect basal concentrations of CH, insulin or

glucocorticoids, nor surges of insulin or glucocorticoids associated

with milking in lactating cattle (Koprowski and Tucker, 1973;
Head et al., 1976).
2. L t

Seasonal changes in the ratio of light to dark may account for
variation in hormone concentrations in mammals. Intensity
(l lux - l lumen of light per m2), wavelength (nm) or periodicity
(number and length of light-dark cycles per 24 hr) of light may modify
effects of photOperiod.

Rod cells located in the retina of the eye are the primary
photoreceptors in mammals. Rods convert light energy to nerve impulses
which eventually affect synthesis of the biogenic amines, serotonin
and melatonin, in the pineal gland (Axelrod, 197a). Concentrations of
serotonin are maximal during light exposure, but concentrations of
melatonin and enzymes which convert serotonin to melatonin are maximal
' in the absence of light (Quay, 1963; Klein et al., 1970; Hurtmn
et al., 1968). Furthermore, injections of serotonin or melatonin
directly into the third.ventricle of the hypothalamus caused release
of Prl from the pituitary in rats (Kamberi et al., 1971). In steers,
intravenous injections of serotonin, but not malatonin, caused 3- to
A 4-fold increases in Prl and 2-fold increases in CH as compared with
preinjection concentrations of these hormones in serum (Goodman et al.,
unpublished).

Effects of light on hormone secretions and subsequent repro-
ductive events in laboratory species can be changed if neural connec-
tions between the retina and the pineal gland are disrupted and/or
pharmacologic doses of serotonin or melatonin are injected (Reiter,

1974). Hormone secretion also can be controlled in laboratory species

by increasing or decreasing the number of hours of light exposure
(photoperiod) per 21» hr (Relkin, 1972; Relkin et al., 1972; Reiter,
1975: Kreiger, 1973). This review will focus on effects of photo-
period on hormones rather than on mechanisms whereby light exerts its
effects. '

In a series of sttxlies by Bourne and Tucker (1975). the effect
" of light on Prl in serum was measured in bull calves maintained in .
individual pens at ambient temperatures of 22 C. Light was supplied
from' ”cool-white” fluorescent lamps at an intensity of approximately
600 lux at shoulder height of calves. At weekly intervals, calves
were'bled by jugular venipuncture 1 hr after illumination and 1 hr
before the dark period. Increases in concentrations of Prl followed
and paralleled changes in number of hours of light per day. More
specifically, Prl decreased from 57 to 8 ng/ml serum when calves were
exposed to photoperiods which were decreased sigmoidally from 16 hr
lightsB hr dark (16L38D) to 8L316D over 12 wk. Conversely, Prl
increased from 25 to 100 ng/al serum when bulls were exposed to photo-
. periods which were increased sigmoidally from 8le6D to 16L38D. In a
third experiment (Bourne and Tucker, unpublished), Prl concentrations
‘ increased from 25 to 100 ng/ml during 6 wk when calves were exposed to
photoperiods which were increased linearly from 8L316D to 24L30D.
Almost immediately upon exposure to continuous light, concentrations of
Prl decreased, and after 5 wk of continuous light concentrations of
Prl averaged 50 ng/ml. Thus, Prl in serum of prepubertal bulls was
greater during daily exposures of 16 hr than during exposures to either

8 hr or continuous light.

Injection of thyrotropin releasing hormone (TRH) markedly
increased concentrations of Prl, on and ten in sera of cattle (Schau.
1972: Convey et al., 1973; Kelly et al., 1973, Davis et al., 1977).
Furthermore, TRH has been injected to test the capacity of the anterior
pituitary to release these hormones under a variety of physiological
conditions, including those caused by photoperiod treatment. For
example, Bourne and Tucker (unpublished) injected TRH at the end of 2
wk of daily exposure to 8 hr of light, on the day an increasing
photoperiod first reached 2h hr, and after 5 wk of daily exposure to
continuous light. In this experiment, concentrations of Prl 5 min
after injection of TRH averaged 270. 2050 and 90¢» ng/ml, respectively.

In sheep exposed to changes in hours of daily exposure to light
which reflected yearly light cycles, Prl concentrations in serum were
directly proportional to changes of photoperiod (Pelletier, 1973).
Serum Prl concentrations were greatest upon exposure to 16L38D photo-
periods and least when exposure was 8L316D. Forbes et al. (1975)
reported that lambs exposed to 16L38D photoperiods for ll wk had
greater Prl concentrations (262 ng/ml serum) than lambs exposed to
8L316D photoperiods (12h ng/ml serum). Release of Prl during milking
decreased gradually from August to December in goats exposed to natural
daylongths: however, if goats were exposed to 17 hr of light per’day
between August and December, release of Prl during milking was main-
tained (Hart, 1975).

Farmer and Follett (1966) proposed that the effect of light on
hormone secretions was not due to total number of hours of light per

2“ hr day, but was due to light during a ”photosensitive” period.

Thus, in sheep exposed to light pulses of 1 hr at the 11th, 14th, 17th
and 20th hr after the beginning of a 7 hrprining period of light,
serum Prl concentrations exceeded Prl concentrations observed when
sheep were exposed to 8L316D photOperiods (Ortavant, 1977). Serum Prl
,concentrations were greatest in sheep exposed to 7 hr of light followed
by 1 hr of light during the 17th hr, an indication that the photo-
sensitive period may occur at this time. I

Although hormone data are lacking, testicular size was maintained
in hamsters exposed to 6 hr of light followed by 30 or 5“ hr of dark,
while testicular regression occurred in hamsters eXposed to 6 hr of
light followed by 18 or 152 hr of darkness (Elliott et al., 1972:
Stetson et al., 1975). These data support the concept that the photo-
sensitive period in hamsters occurs every 12.5 hr after initial
exposure to light (Gaston and Henaker, 1967). Light occurred during
the photosensitive period every 1.5 to 2.5 days in those hamsters
exposed to 6 hr of light followed by 30 to 5# hr of darkness.

.In bull calves (Bourne and Tucker, 1975) and wether lambs
(Driver et al., 1976), average concentrations of CH were not affected
by 8Li16D or 16L38D photoperiods. However, rats exposed to constant
darkness had lower GB concentrations in pituitary and plasma as com-
pared with rats exposed to either constant light or 10 hr of light per
day (Relkin, 1972).

Information on effects of photoperiod on glucocorticoid concen-
trations and effects of more extreme photoperiods on other hormones is
limited for domestic livestock. Wavelength and intensity of light may

affect hormone secretion. For example, decreasing number of hours of

light exposure per day retarded development of the testes in chickens;
but, in comparison with blue or green light, this effect was greatest
_in birds.eXposed to white light or light from the red portion of the
visible light spectrum (Harrison et al., 1970). In female rats, con-
tinuous exposure to white light caused persistent estrus and retinal
degradation (Lambert, 1975a). If continuous light was from the red
1 portion of the visible light spectrum, or light intensity was less
than 25/uu cm2, persistent estrus occurred without retinal degradation
(Lambert, 1975a, b). In birds, intensity of light required for regu-
larity of locomotor activity (0.1 lux) was less than intensity of
light (7 to 10 lux) required to initiate seasonal testicular changes
(Menaker, 1971).
3. Temperature

Hettemann and Tucker (197“) reported that Prl in Holstein
heifers maintained on 12L312D photoperiods increased or decreased
approximately 1 ng/C per hr when temperatures were either increased
from 21 to 27 C or decreased from 21 to 10 C over a hr. Serum Prl
concentrations in heifers continually exposed to 27 or 10 C temper-
atures for 5 days increased 200% or decreased 38% as compared with
serum Prl concentrations at 21 C. Increase in Prl following injections
of 10 ug‘TRH was greater in heifers exposed to 27 C (120 ng/ml serum)
than in heifers exposed to 10 c (62 ng/ml serum). If heifers were
exposed to 32 or'4.5 C for'5 days, Prl concentrations increased by
115% or decreased by 775. in comparison with heifers at 21 C (Tucker
and Hettemann, 1976). In addition to decreases in serum Prl concen-

trations caused by chronic exposure to #.5 C, release of Prl following

10

injection of TRH was abolished at this temperature. Metabolic clear-
ance rate (MGR) of Prl in steers was increased at 10 C and decreased
at 30 c (Smith et al., 1977). Increased clearance of Prl at low
temperatures may explain partially the low concentrations of Prl in
heifers subjected to 4.5 C, but increased clearance alone cannot
account for the temperature dependent release of Prl following TRH
administration (Smith et al., 1977).

Although CH concentrations in serum tended to increase with
increased ambient temperatures, average concentrations were not sta-
tistically different after 5 days exposure to 4.5, 21 or 32 C (Tucker
and wettemann, 1976). If temperatures exceeded 35 c for u hr, GH in
serum increased to concentrations twice those observed at 18 c (Mitre
and Johnson, 1972): but, after 5 wk exposure to 35 C, CH secretion
rate, estimated from disappearance rates, was decreased (Mitra et al.,
1972).

In a review of effects of temperature on reproduction and lac-
tation, Thatcher (1974) reported decreased release of glucocorticoids
following exogenous adrenocorticotropin (ACTH) treatment in cattle
exposed to temperatures greater than 21.1 C as compared with release
observed in cattle exposed to temperatures less than 21.1 C. In heifers
exposed to diurnally varying temperatures, glucocorticoids in plasma
were more variable in heifers exposed to temperatures which varied
between 21 and 35 C than in heifers exposed to temperatures which
varied between 17 and 21 C. Average concentrations of glucocorticoids
in the heifers subjected to 21 to 35 C temperatures were greatest

during the first wk, but decreased with time of exposure. In steers,

11

4 hr of exposure to 42 C increased concentration of cortisol in plasma
(Abilay et al., 1975a): however, in heifers expOsed to 33.5 C for two
estrous cycles, glucocorticoids decreased (Abilay et al., 1975b). It
appears that short exposure to high ambient temperatures enhance while
longer exposures to high ambient temperatures depress secretion of
glucocorticoid from the adrenal.

It is not clear how changes in ambient temperature interact with
changes in photoperiod to affect serum Prl, CH or glucocorticoid con-
centrations in cattle. Concentrations of Prl in sera from heifers
exposed to 16 hr photoperiods from November through March or from
April through August were 4- and 1.6-fold greater than Prl concentra-
tions in heifers exposed to natural daylengths during these months
(Peters and Tucker, 1978). Changes in Prl paralleled changes in ambient
temperature in heifers exposed to 16L|8D or natural daylength. However,
temperatures below 0 C decreased the ability of 16L28D photoperiods to
enhance Prl during winter months, and temperatures above 22 C augmented
the effect of 16 hr of light on Prl concentrations during summer months.
Thus, as temperature increased from -7 to 28 C, Prl increased in incre-
ments which were proportionally greater during exposure to 16L38D
photoperiods than during natural light exposure of 9.2 to 15.3 hr.

a. Circadian ththns '

Seasonal effects of environment on hormones and production
traits may have a yearly cycle caused by changes in exposure to light
and/or temperature. Other changes occur naturally with a frequency of
repetition once every 20 to 28 hr (Ringer, 1977). However, feeding

patterns and/or locomotor activity of an animal cause these changes to

12

occur with a 24 hr rhythm (Elliott et al., 1972). In this review,’
reports on hormones which demonstrated one significant increase per
24 hr will be discussed. Increases in hormones which occur during the
light hours of a day are called diurnal increases while increases in
hormones which occur during the dark portion of a day are called noc-
turnal increases.

Variation of Prl in serum in the dairy cow has been reported by
Swanson and Hafs (1971). Koprowski et al. (1972) and Hansel et al.
(1975). Peak concentrations were during daylight hours, at 1600 hr
or during nocturnal sampling, respectively. It is difficult to assess
these findings, since these researchers did not report daily photo-
period exposures not the time of day when animals were fed. Koprowski
et al. (1972) estimated that 8% of the variation of Prl in serum was
associated with diurnal variation.

Variations in Prl have been reported in other animals. For
example, Freeman and Neill (1972) noted that pseudopregnancy in rats
induced a surge of Prl once each 24 hr with a peak at 0300 hr if blood
was collected every 4 hr via chronically implanted aortic catheters.
Re-evaluation of this phenomenon using blood collected by decapitation
revealed two surges per 24 hr, one between 1500 and 1700 hr and the
other between 0300 and 0700 hr (Freeman et al., 1974). Thus, cannula-
tion and multiple blood sampling of the rats eliminated the diurnal but
not the nocturnal surge.

In normal male rats, Ronnekleive et al. (1973) observed an early
morning surge of Prl beginning at 0300 hr. In contrast, Sinha et al.

(1977) found an increase in Prl beginning at 1500 hr. Descriptions of

13

the environmental and experimental conditions for these experiments
were similar: perhaps some unrecognized form of "stress” of the animals
accounts for divergent results. For example, Dunn et a1. (1972) com-
pared Prl concentrations from rats which were: (1) ether stressed
prior to bleeding: (2) confined in small cages prior to bleeding;

(3) rapldly decapitated upon removal from their cages. The daily peak
of Prl in the ether-treated and confined rats occurred at 1700 hr,
whereas in rapidly decapitated rats the peak was at 2300 hr.

Studies on daily rhythms of other hormones in domestic ruminants
are scarce. Hove and Blom (1973) discovered a daily increase in
insulin in 14 cows, and this surge of insulin was associated with
feeding patterns. Daily patterns were not found for CH in serum of
cattle (Koprowski et al., 1972; Hove and Blom, 1973).

Information on variation of glucocorticoids is limited for the
dairy cow. Macadam et al. (1972) claimed that greatest concentrations
occurred between 0230 and 0630 while lowest values were at 2030.
Similarly, wagner and Oxenrider (1972) reported that concentrations
were lowest between 1800 to 0200 hr in cattle. In contrast, Hudson
et a1. (1975) observed that diurnal variations of glucocorticoids were
absent in cattle. Details of experimental conditions such as season,
photoperiod and temperature were not reported and may account for the
divergent observations.

In sheep fed ad libitum and exposed to 16L38D photoperiods,
cortisol concentrations were maximal at 0930 hr (McNatty et al., 1972);
however, in sheep fed once per day and exposed to 14L310D photoperiods,
glucocorticoids increased once at 0400 hr prior to daybreak and again

at 1600 hr prior to feeding (Holley et al., 1975). After sheep were

l4

confined to cages or eXposed to a new environment, glucocorticoid con-
centrations increased, but were not regular for as few as 6 and as many
as 28 days (Holley et al., 19753 McNatty and YOung, 1973).

Rats reared under continuous light or continuous dark from birth
do not manifest a daily periodicity of glucocorticoid secretion; but a
periodicity will develop if rats subsequently are exposed to alter—
nating light-dark photoperiods (Krieger, 1973). Normally in rats
exposed to 12L312D photoperiods, peak concentrations of glucocorticoids
occurred just prior to dark. For example, when light exposure occurred
between 0700 and 1900 hr, glucocorticoid concentrations were maximal
at 1800 hr (Takahashi et al., 1977). and when light exposure occurred
between 0800 and 2000 hr, glucocorticoid concentrations were maximal at
g 2000 hr (Krieger, 1973). Normal periodicities of established release
patterns for glucocorticoid do not persist if rats subsequently are
enucleated, exposed to constant light or exposed to constant dark. In
fact, in rats initially exposed to light between 0700 and 1900 hr and
then exposed chronically to constant light, maximal concentrations of
glucocorticoids in serum shifted from 1800 hr at a rate of 2 to 3 hr
each 24 hr. Such studies demonstrated that time of maximal glucocorti-
coid concentrations is dependent on number of hours of light and may
be synchronized by regular light-dark cycles.

(Thus, it is possible that circadian rhythms in glucocorticoid
secretion patterns may be influenced by seasonal changes in length of
photoperiod. In wild birds, Meier (1972) noted that peaks of gluco-
corticoids occurred at 0300 hr during May and at 2100 hr in August.

In these same birds, Prl concentrations were maximal at 1500 hr in May

15

and at 0500 hr in August. Hhen Meier exposed birds to 24L30D photo-
periods to minimize effects of light-dark cycles, concentrations of
Prl in serum increased 12 hr after exogenous glucocorticoid injections.
This temporal relationship between glucocorticoid injection and Prl
surge was similar to the relationship between maximal concentrations
of glucocorticoid and Prl observed in wild birds during May. In fact,
birds treated with exogenous glucocorticoids became fat: a character-
istic exhibited in wild birds during May. Meier suggested that seasonal
factors which affected glucocorticoid and Prl secretion patterns also
may affect the way the two hormones synergize to affect body growth or
reproduction. A

Joseph and Meier (1974) tested Meier's hypothesis of a synergism
between daily rhythms in glucocorticoids and Prl concentrations.
Groups of female hamsters were injected with ovine Prl at 0, 6, 12, or
18 hr after a glucocorticoid injection (24L30D light exposure).
Estrous cycles were lengthened in those groups treated with Prl 18 hr
after the start of the photoperiod or in hamsters treated with Prl 12
hr after a glucocorticoid injection. Hamsters in other treatment
groups exhibited normal estrous cycle lengths. Perhaps the same factors
which cause hamsters to exhibit constant estrus behavior when Prl is
injected 18 hr after the start of a 12L112D photoperiod are involved if
Prl is injected 12 hr after a glucocorticoid injection.

Perhaps a temporal relationship exists between Prl and gluco-
corticoid increases in cattle. Treatment of dairy heifers with flu-
methasone, a synthetic glucocorticoid, abolished the nocturnal eleva-

tion of Prl observed in control heifers (Hansel et al., 1975).

l6

'5. Feeding

 

Little is known about the association of hormones with feeding
and locomotor activity in cattle. Stricklin (1976) reported that
cattle ate in groups shortly after sunrise or prior to sunset in summer
and winter, although individual animals ate at intervals dispersed
throughout the day. Time spent eating increased by 5 hr during the
summer trials as compared with time during the winter. However,
quantity of feed consumed was not increased in Holstein heifers exposed
to 16 hr of supplemental fluorescent light during fall and winter in
comparison with heifers exposed to natural daylongths of 9.0 to 11.5
hr (Peters et al., 1975). Hormone data were not available in these
studies.

I Johke (1970) noted brief increases in concentrations of Prl in
sera taken from cattle shortly after they had eaten. McAtee and
Trenkle (1971) observed that Prl concentrations in serum of cattle
increased from 12 to 23 ng within 6 hr after eating, while values
observed just after a fast averaged 2 ng/ml.

Although time of feed intake and concentrations of GH in serum
were not related in sheep (Trenkle, 1971) or cattle (Hove and Blom,
1973), CH was elevated if animals were fed high roughage or low energy
diets. In a study using fasted lactating cows, Reynaert et a1. (1975)
concluded that any treatment which decreased nonesterified fatty acids
(NEFA) in serum would increase concentrations of CH in serum. For
example, nicotinic acid, an antilipolytic agent, caused increases in
CH concentrations which were three times greater than increases
caused by insulin, glucose, arginine, propranalol and two other anti-

lipolytic agents. Magnitude of CH released was diminished if volatile

l7

fatty acids were administered simultaneously with the antilipolytic
agents.

Following restricted feed intake, Prl increased from 36 to
214 ng/ml of serum but CH decreased from 20 to 10 ng/ml of serum in
lambs fed ad libitum for 11 wk (Forbes et al., 1975; Driver et al.,
(1976). Similarly, in cattle each time energy balance was altered,
changes in concentrations of Prl and CH were inversely related to one
another (Swan, 1976).

In laboratory species time and duration of feeding may alter
circadian rhythms of glucocorticoid concentrations. In control rats
fed ad libitum, concentrations of glucocorticoids peaked at 1600 hr,
just prior to onset of darkness; however, if rats were restricted to
4 hr of feed intake, glucocorticoid concentrations decreased and
circadian rhythms were not obvious (Philippens et al., 1977). Con-
versely, Nelson et a1. (1975) found circadian changes in glucocorticoid
concentrations of meal-fed rats were increased in amplitude when com-
pared with ad libitum fed rats.

In rats initially adapted to 12L312D photoperiods, intake of food
and concentrations of corticosterone in serum were maximal at 1800 hr
(Takahashi et al., 1977). After chronic exposure of rats to continuous
(24L30D) light, time of maximal food intake and of maximal gluco-
corticoid concentrations shifted from 1800 hr at a rate of 2 hr per
24 hr.

In control rats fed ad libitum, maximal glucocorticoid concentra-
tions were observed just prior to the dark period. When rats were

allowed only 2 hr access to food and water per 24 hr, maximal increases

18

in glucocorticoid concentrations appeared just prior to time of food
and water intake whether the 2 hr access was in the photoperiod or in
the scotoperiod (Krieger et al., 1977). This implied that circadian
increases in glucocorticoids were associated with intake of feed and

water.

B. Changes in Hormones Associated with Body Growth and Lactation

Hormone concentrations in sera of domestic mammals change during
growth and lactation. These changes may reflect increased amplitude,
duration and/or frequency of release from the pituitary. The primary
focus in this section of the review of literature will be the discussion
of changes in concentrations of Prl, CH and glucocorticoid associated
with body growth and lactation in cattle.
1. Prolactin

In cattle, an association between Prl, growth and puberty has
been proposed but not proven. Gonzalez—Padilla et a1. (1975) defined
puberty in.catt1e as the day of the first LH peak preceding corpus
luteum (CL) formation. Patterns of concentrations of serum Prl prior
to puberty in heifers did not change between 6 and 15 mo of age.
However, Prl concentrations and initiation of pubertal changes, espe-
cially mammary growth, may be related at an earlier age. For example,
Sinha and Tucker (1969) observed a 333% increase in pituitary Prl con-
centrations between birth and 3 mo of age in Holstein heifers. Mammary
tissue was sampled from five heifers each month from birth to 12 mo of
age, and deoxyribonucleic acid (DNA) content of the tissue was used to

estimate increases in mammary cell numbers. Content of DNA increased

19

1.5, 3.5 and 1.6 times faster than body weight in the intervals of 1
through 3, 3 through 9 and 9 through 12 mo of age, respectively. The
increase in DNA content of the mammary gland was most rapid between 3
and 9 mo of age when pituitary Prl concentrations were greatest. In
addition to increases in pituitary Prl content and rate of mammary
development, Prl concentrations in serum increased 3- to 4-fold between
1 and 3 mo of age in dairy heifers (Leining et al., 1976: Davis et al.,
1977). Thus, changes of Prl concentrations in pituitary and serum
between 1 and 3 mo of age may indicate a critical stage of development
in dairy heifers.

Prepubertal dairy bulls (McGuffey et al., 1977) and heifers
(Davis et al., 1977) treated with TRH (which causes release of Prl, CH
and TSH) grew 10% faster than their respective saline-injected controls.
In McCuffey's study, Prl released after administration of TRH (500
ug/bull per day) increased as the experiment progressed. Since all
calves started treatment during December and January, increasing
temperature and daylength could account for this response. In the
' Davis study. after 6 months of TRH treatment (50 pg, Zx/heifer per day),
(THH no longer caused release of Prl or TSH. Average age at first estrus
was 9.4 no in TRH-injected heifers, 1.1 no earlier than in control
heifers. It is not clear whether enhanced growth or sexual maturity
in TRH-treated.cattle was related to increases in Prl, CH or TSH,
some combination of the three hormones, or if other factors were
involved.

Other studies in rats, sheep and hamsters also suggest a relation-

ship between Prl and onset of puberty. For example, Prl concentrations

20

in serum were low from birth until day 19 in male and female rats, but
increased from day 19 to puberty (the peripubertal period was days 37
to 43 when male rats exhibited LH surges and female rats exhibited
vaginal opening) (Negro-Vilar et al., 1973; Dohler and Huttke, 1975).
Subsequent increases in Prl concentrations after day 19 were correlated
positively with increases in progesterone (Prog), and negatively with
luteinizing hormone (LH) and follicle stimulating hormone (FSH).
Ravault and Courot (1975) noted a sharp increase Of Prl concentrations
in serum and sperm development at 10 to 12 wk of age in ram lambs born
in the fall. High Prl concentrations associated with spring and summer
months may have concealed relationships between Prl and testicular '
' function in rams born in the spring (Ravault et al., 1977). Research
with hamsters suggested that Prl enhances LH binding and testicular
function (Bartke, 1975; Bex and Bartke, 1977).

. Evidence for the action of Prl on initiation (lactogenesis) and
maintenance of lactation in the dairy cow has been indirect. Cowie
(1976) discussed research in cows, sheep and goats which indicates CH
has a greater role in galactopoiesis than does Prl; as early as 1937
Asimov and Krouze reported that injection of dairy cows with CH-rich
bovine pituitary fractions caused greater increases in milk yield than
injection of Prl-rich fractions.

An increase in Prl may be required for initiation of maximal
milk secretion in cattle. A marked surge in peak concentration of .
Prl in serum occurred 1 day prior to parturition in dairy cattle
(Ingalls et al., 1973). When TRH was given to dairy cows near partur-

ition, subsequent milk yields were increased over performance in prior

21

lactations (Karg and Schams, 1974). Although TRH releases Prl, CH
and TSH in cattle, Karg and Schams claimed that release of Prl was
critical for enhanced milk production. Bauman et a1. (1977) reported
evidence which may support this hypothesis. Injections of a tranquil-
ising drug, reserpine, increased Prl but not CH or glucocorticoids in
sera of cows induced to lactate with steroid hormones. In addition,
reserpine-treated cows had greater milk yields than control cows
treated with steroid hormones alone. Furthermore, when 2-Br-a- A
ergocryptine was used to block the surge of Prl at parturition, sub-
sequent milk yields were depressed 20 to 80% (Fell et al., 1974; Karg
and Schams, 1971+). Fell et a1. (1971.) found a depression of Prl con-
centrations in serum of cows injected with ergocryptine after partur-
ition, but milk yield and percent protein decreased only in those cows
which were lactating less than 2 wk.

Milking stimulated release of Prl in dairy cows (Tucker, 1971;
Fell et‘ al., 1971). Serum Prl increased within 1 to 3 min if teats were
stimulated without subsequent milk removal (Reinhardt and Schams. 1975).
This response is not necessarily associated with milk letdown, because
injections of oxytocin without teat stimulation did not cause release
of Prl (Koprowski and Tucker, 1971; Karg and Schams, 1974). Koprowski
and Tucker (1973) reported that Prl released at milking was correlated
(r'- 0.36) with milk production. However, when ergocryptine was used
to block milking-release of Prl in cows with well-established lactation,
milk production was not affected (Karg et al., 1972; Smith et al., 1974;
Beck. 1977).

Most reports suggest that Prl concentrations are not altered

22

significantly during the estrous cycle of the lactating cow. However,
releases of Prl after milking tended to be smaller during estrus
(Koprowski and Tucker, 1973) or after injection of TRH 2 to 4 days after
estrus (Vines, 1976) than during the rest of the estrous cycle.

Basal concentrations of Prl in serum were not altered during
concurrent lactation and pregnancy, nor did pregnancy significantly
affect Prl released during milking (Koprowski and Tucker, 1973).

Posner et a1. (1975) found that Prl receptors were induced in
livers of hypophysectomized female rats bearing anterior pituitary
homografts under the kidney capsule (a condition which notably increased
concentrations of Prl in the serum). Conversely, number and affinity .
of Prl receptors increased independently of Prl concentrations during
advanced pregnancy and onset of lactation in ergocryptine-treated
rabbits (Djeane et al., 1977). The importance of concentrations of
Prl in sera versus concentrations and activity of Prl receptors has
not been explored in cattle. However, increased concentrations of Prl
which occurred between 1 and 3 mo of age and during the periparturient
period in cattle may be critical for body growth and lactation if Prl
can induce its own receptors at target organs.

2. Growth Hormone

Armstrong and Hansel (1956) claimed that age and diet did not
affect total CH content of pituitaries from Holstein heifers. However,
when CH was expressed on a body weight basis, concentrations were
greatest in younger animals. Similarly, pituitary CH was greater in
newborn bulls than in weanling or feedlot steers (Curl et al., 1968).

In contrast, when bull calves were sampled at monthly intervals from

23

birth through 12 mo of age, Purchas et a1. (1970) found that on con-
centrations in anterior pituitaries decreased between birth and 1 mo
of age, but increased between 2 to 4 mo. Furthermore, CH concentrations
in plasma were not correlated significantly with pituitary concentra-
tions. Tucker et a1. (1973) found that CH concentrations in serum
increased between 3 and 5 mo of age in Holstein heifers. As discussed
earlier in this review, rapid increases in mammary tissue and high
pituitary concentrations of Prl also occurred at this age. Despite
these changes in mammary growth and CH in young heifers, CH concen-
trations measured between 3 mo of age and the 26th day of lactation
were not correlated significantly with each other nor with subsequent
lactational performance of the heifers.

Some researchers observed increases in CH following a TRH chal-
lenge in young ruminants while other investigators did not. Treatment
with TRH in rapidly growing wether lambs (Davis et al., 1976) or
heifers (Davis et al., 1977) did not increase CH concentrations in
serum significantly, yet growth rate was enhanced. In contrast,
McCuffey et a1. (1977) reported release of on after administration of
rah in bull calves. Moreover, Vines et a1. (1976) demonstrated that
CH concentrations prior to IV injections of TRH were correlated
(r'- 0.6) with TRH-induced release of the hormone in prepubertal
heifers. Whether discrepancies in results reflect differences in dose
of TRH injected into the ruminants or differences in laboratory pro-
cedures remains to be elucidated.

As early as 1954, Clegg and Cole reported that heifers, but not

steers, treated with diethylstilbestrol (DES), an estrogen-like growth

24

stimulant, had twice the pituitary concentrations of CH observed in
controls. Trenkle (1970) found that DES treatment doubled on in serum
and increased pituitary weights. Although he found a negative relation-
ship between growth and serum CH concentrations, Trenkle stressed that
this relationship may not be meaningful. The steers were studied at
the fattening stage and CH may effect only lean tissue weights.
Similarly, Borger et al. (1973) observed that treatment of steers with
' Zeranol, a corn-distillers byproduct, doubled CH concentrations in
serum when compared with concentrations in control steers. Insulin
and glucose in serum were elevated also. Zeranol-treated steers may
have had greater water retention and less fat deposition than control
steers.

Data collected from other species imply a relationship between
CH concentrations and partition of energy between fat deposition and
increase of lean tissue. Swine selected for high backfat had lower
concentrations of CH in serum and pituitary than controls or pigs
*selected for low backfat (Althen and Gerrits, 1976). Genetically
obese rats, homozygous for the ob gene, also had lower serum and pitu-
itary on than their lean litter mates (Sinha et al., 1975). Sinha
et a1. (1976) reported that obesity may be the cause of decreased on
concentrations, and that the condition may affect secretion of Prl as
well. Basal Prl and CH concentrations are decreased in rats made
obese with goldthioglucose (CTC) or bipiperidyl mustard. Perphenazine,
an anti-anxiety drug, released Prl in rats made obese by CTC treatment
when they were obese but not when they were lean.

In dairy cows, parturition (Ingalls et al., 1973; Reynaert et al.,

1976), but not milking (Tucker, 1971; Koprowski and Tucker, 1973b),

25

increased CH concentrations in serum. Concentrations of CH averaged
h.3 ng/ml at 26 days prior to parturition and increased to nearly

lo ng/ml serum at parturition. Although concentrations then decreased
within h days to an average of 5.0 ng/ml, CH was greater during early
lactation than during late pregnancy. Similarly, TRH-induced release
of CH was greater at 2 mo of lactation than at later stages (Vines,
1976).

Injections of CH alone increased milk yields in dairy cattle
(Donker and Petersen, 19513 Bullis et al., 1965; Hachlin, 1973). More-
over, when concentrations of CH, Prl and TSH in serum were enhanced by
TRH treatment for 10 days, milk yields increased 0.66 kg per cow during‘
the last 5 days of treatment (Convey et al., 1973). In contrast,
Kelly et a1. (1973) did not find an elevation in milk yield, although
TRHincreased Prl in cows during advanced stages of lactation.
Therefore, it is not clear which of the hormones released following
TRH injection caused increased milk yield in the study of Convey et a1.
‘(1973).

In dairy cattle, CH concentrations in serum decreased as lacta-
tion advanced if data were adjusted for stage of pregnancy and season
(Koprowski and Tucker, 1973b) or forage diet (Smith et al., 1976).
Research suggests that CH may be mobilizing body fat stores early in
lactation in dairy cattle when feed intake may not be adequate to meet
energy needs. Reynaert et al. (1976) and Belyea et al. (1976) noted
NEFA's and serum CH concentrations were greatest at parturition and
decreased during the first 90 days of lactation. Kronfeld (1965)

injected dairy cattle with exogenous CH and observed increased NEEA's

26

' in plasma. Significant increases in plasma NEFA's are usually the
result of rapid breakdown of triglycerides in adipose tissue. Thus,
exogenous CH may enable NEFA's from adipose tissue to be used as energy
for body maintenance or for milk synthesis. For example, in compar-
isons between beef and dairy cattle paired for body weight and stage
of lactation, dairy cows had greater concentrations of CH, while Prl,
insulin and glucose concentrations were greater in beef cattle (Hart
et al., 1975). Milk production was 120 kg per wk greater in dairy
cows than in beef cows, although both types of cattle were fed to match
intake of the beef cattle. Conversely, body weight of beef cattle
increased 10% between parturition and 15 wk of lactation, but body
weight of dairy cows decreased nearly 10% during the same interval.
'Again this may imply that CH concentrations in sera from dairy cattle
allow them to mobilize body fat stores or to increase feed efficiency
for milk production. Injections of exogenous CH decreased the amount
of feed needed to synthesize 1 kg of milk from 1.77 to 1.26 (Machlin,
1973); however, the decrease in this ratio was due to increased milk
production rather than decreased feed intake. Similarly, when cows
winjected with exogenous CH for 6 days were fed at 100% of total digest-
ible nutrient requirements, milk yields increased 50% (Chung et al.,
1953). Yet, even when TDN intakes subsequently were restricted to h0%
of requirements, milk yields were maintained in cows injected with CH.
In summary, CH may be involved in the partition of energy between
‘ lean tissue and fat during growth and between milk production and fat
during lactation. Since increases in CH concentrations in cattle

normally occur between 3 and 5 mo of age and at parturition, these may

27

be critical and controllable stages of development. However, as with
Prl, the importance of concentrations of CH in sera versus concentra-
tions and activity of CH receptors at target tissues has not been
explored in cattle.
3. Clucocorticoids

Relative to information available on Prl and CH, there are few
reports on normal variation of glucocorticoid concentrations in the
rapddly growing calf. However, some stimu11.which affect Prl or CH
also alter concentrations of glucocorticoid in cattle. For example,
Convey et a1. (1973) found that within 10 min after injection of TRH
at doses of 25, 50 and 100 ug/cow, glucocorticoids were increased from '
1 to nearly 9 ng/ml serum above preinjection values of 3 to h ng/ml
serum. In contrast, Vanjonack and Johnson (1975) observed a 3- to
h-fold decrease in glucocorticoids from preinjection concentrations
(18 to 25 ng/ml plasma) 29 to #5 min after 200 or 400 pg of TRH were
injected. Discrepancies between results of these two studies may
reflect differences in experimental procedures: however, concentrations
of glucocorticoid prior to injection of TRH may affect the actions of
TRH on glucocorticoid release in cattle. Louis et a1. (1974) observed
a six-fold increase in glucocorticoids following intramuscular injec-
tions of prostaglandin 221 (PCF-Za), a substance which also released
pituitary Prl, CH and LH in cattle. However, glucocorticoid concen-
trations were not affected after injections of either ergocryptine,
which depressed Prl (Smith et al., 1971+), or reserpine. which enhanced
Prl in serum (Bauman et al., 1977).

Heifers fed melengestrol acetate (MCA), a synthetic progestin,

28

had less plasma cortisol, adrenal cortisol and adrenal corticosterone
concentrations than control heifers (Purchas et al., 1971). Heifers
treated with MCA grew nearly 10% faster than untreated control heifers,
yet CH concentrations were significantly lower in serum of HCA-treated
heifers. The ratio between CH and glucocorticoid concentrations may
be more important for growth than absolute concentrations of either
hormone alone.

Reports on laboratory species, sheep and goats suggest that
glucocorticoids are needed for development and secretion of the mammary
gland (Tucker, 197a). For example, Anderson and Turner (1963a, 1963b)
demonstrated that the adrenal gland was necessary for maintenance of
reproduction in the rat from conception through pregnancy and lactation.
A combination of gluco- and mineralcorticoids restored normal function
in adrenalectomized rats, but requirements of glucocorticoid for lac-
tation were 2- to 5- times greater than requirements for normal.
mammary growth. when lactating rats were maintained at a high suck-
ling intensity (litters were replaced with 8-day-old litters on days
16 and 2“) from day 16 through 32 of lactation, adrenal corticosterone
content and concentration decreased linearly (Thatcher and Tucker,l
1970b). Along with decreased adrenal glucocorticoid concentrations,
gain.in litter weight decreased from 80 g to an average of 30 g per
litter between 2“ and 32 days of lactation. This suggests that
decreased availability of glucocorticoids limited milk production,
because milk yields (measured by litterweight gain) could be maintained
(when rats were supplemented with the synthetic glucocorticoid,
9-f1uoroprednisolone acetate (Predef), injections (Thatcher and Tucker,

19703).

29

In cattle, concentrations of endogenous glucocorticoid increased
in the final days of gestation to peak concentrations at the time of
parturition (Smith et al., 1973). The milking stimulus (Koprowski
and Tucker, 1973a) and exteroreceptive stimuli associated with milking
(Smith et al., 1972) also released glucocorticoid in dairy cows.
However, milking-induced release of glucocorticoids was not signif-
icantly related to milk yields (Koprowski and Tucker, 1973b).

In contrast, evidence suggests that dose of exogenous gluco-
corticoid and time of injection of glucocorticoid relative to stage of
lactation affect milk yields in cattle. For example, when dexametha-
sone was injected in cattle at doses of 10 mg twice daily, glucose
concentrations in plasma increased, mammary blood flow decreased, and
(milk production decreased 5 kg (Hartmann and Kronfeld, 1973).
Decreases in milk yield were similar in cattle injected with ACTH in
doses ranging from 160 to #00 IU (Brush, 1960; Campbell et al., 1964).
Nevertheless, small doses of synthetic glucocorticoids may enhance
milk production if treatment commences early in lactation. Swanson
and Lind (1976) reported that oral doses of flumethasone (up to 10 mg
per day) starting on day 4 of lactation increased milk production in
dairy cattle, although length of lactation was decreased if 20 pg of
the drug were fed. If flumethasone treatment started at day 28 (Head
et al., 1976) or later (Swanson and Lind, 1976) there was no effect on
milk yield. The study by Swanson and Lind may have been successful
because mammary epithelial maturation is not complete prior to partur-
ition or in early lactation (Akers et al., 1977) and epithelial cells

may be sensitive to hormone control at this time. Thus, it is not

30

surprising that Tucker and "sites (1965) observed induced lactation in
pregnant heifers injected with Predef. In addition, the amount of
Predef needed decreased and the amount of milk secreted increased as
pregnancy advanced.

Further research may be needed on the association between gluco-
corticoid concentrations and associated growth or lactation traits in
cattle. Factors of importance could includes (1) the relationship
between glucocorticoids and other hormones related to growth (especially
CH and Prl) and (2) the relationship between glucocorticoid concentra-
tions and mammary epithelial cell development and milk yield in early

lactation.

MATERIALS AND METHODS

A. Animals

Holstein bulls, ranging from 5 to 18 wk of age and from 52 to
150 kg body weight at the beginning of experiments, were used in these
studies. Bulls were paired by body weights and randomly assigned
within pairs to one of two rooms of an environmental chamber. Four
bulls were assigned per room.

Bulls were fed a complete pelleted ration, trace mineralized salt
(see appendix), and water ad libitum except at times when multiple
blood samples were drawn. Feed consumption per 2“ hr in each group of
'bulls was measured twice weekly on days when blood was collected for
hormone analysis. In addition, gain in body weight was estimated on

each bull by heart girth (cm) measured twice weekly.

B. Environmental Chambers

Two rooms, each housing four calves, were used in these experi-
ments. The rooms were nearly equal in size; one room contained approx—
imately 35 m3 of air and had 9.4 m2 floor area, while the other room
held 31 m3 of air and had 9.3 m2 floor area.

Temperature was maintained between 18 and 22 C. Humidity was
monitored with a sling psychrometer (Taylor, Sybron Corp, Arden, NC)
and ranged from 60 to 70%. Halls and ceilings of the chambers were

painted with white epoxy paint containing titanium dioxide type III
31

32

pigment base (Pratt and Lambert, 00.). Titanium dioxide pigment base
was selected because it reflects light between 425 and 900 nm in the
same proportion as emitted by the light source (Bickford and Dunn,
1972).

Hours of light exposure per 24 hr were controlled automatically
by Intermatic time clocks (Spring Grove, IL). Measurements of light
intensity or spectral energy were taken 1 m from the chamber floor with
a Luna-Pro light meter (Cossen CMBH, Erlangen, H. Germany) or a spec-
troradiometer (Instrument Specialties, Co. (ISCO), Lincoln, NE),
respectively. Different light sources were used in each experiment,

and will be reported in section E, Objectives and EXperimental Design.~

C. Blood Sampling Procedures

At the midpoint of the photoperiod on Tuesday and Friday of each
week of the experiments, blood was collected by jugular venipuncture
from all bulls. One person haltered and held each calf while a second
person collected blood with 10 ml BD Vacutainers (100 x 16 mm)
equipped with a 2.54 cm 20 ga BD Vacutainer needle (Becton Dickinson
and Co., Rutherford, NJ).

In studies involving multiple sampling of blood, such as TRH
challenges, Prl infusions or studies of diurnal variation, bulls were
cannulated in the jugular vein 12 to 24 hr before blood collection.
Polyvinyl cannulas (V10 tubing, Bolab, Inc., Derry, NH) were inserted
into a jugular vein by 12 ga thin-walled needles (Becton Dickinson
and Co., Rutherford, NJ). To prevent blood coagulation, cannulas were

filled with sodium citrate (3.5% in sterile water) between blood

33

collections. Hhen the time between collection of samples exceeded

12 hr, bulls were allowed to move freely in their pens to obtain food
and water. To protect indwelling cannulas at these times, the bulls'
necks were wrapped with 7.62 cm wide Elastoplast (Beiersdorf, Inc.,
South Norwalk, CT) and secured with safety pins.

Prior to the start of TRH challenge or Prl infusion experiments,
blood was collected and discarded each 30 min for 2 hr to condition
bulls to the sampling procedure. Such conditioning is necessary to
establish stable baseline values for prolactin (Raud et al., 1971;
Tucker, 1971). To estimate the effect of "stress" of blood sampling
methods in these experiments, concentrations of Prl (-30 and 0 min
samples) and CH (-15 and 0 min samples) in sera collected through
cannulas prior to TRH challenges were compared with concentrations of
these hormones in the two samples collected by venipuncture during the
'week of the TRH challenge. Details of blood sampling procedures
which were peculiar to individual experiments will be discussed in
Section E, Objectives and Experimental Design.

All blood samples were allowed to clot for 1 to 2 hr at room
temperature and stored at 4 C for 24 hr before centrifugation at
1000 x g for 20 minutes. Serum was decanted and stored at -20 C

until assayed for hormone concentrations.

_Q,V Hormone Assays
Double antibody radioimmunoassays were used to measure protein
hormones. Three major principles of these assays are (1) specific

antibodies are used which bind specific hormones, (2) hormones can

34

displace their radioactive ligands from the antibody and (3) hormone
concentrations are obtained by comparison of unknowns to a series of
tubes containing known amounts of standard reference hormones.
Sources of standards and estimates of variability of radioimmuno-
assays used in this study are reported in Table 1. Estimates of
variability in these assays were from ng/ml values obtained from a
series of dilutions of a common serum pool. Complete descriptions of
these assays have been reported as follows: prolactin, Tucker (1971),
Koprowski and Tucker (1973b): luteinizing hormone, Oxender et a1.
(1972); thyrotropin, Borger and Davis (1974), Kesner et al. (1977).
Clucocorticoids were measured by competitive protein binding assay
(Smith et al., 1972).

‘ Kits purchased from Radioassay Systems Laboratories, Inc.
(Carson, CA) were modified to analyze L-thyroxine (T4) in bovine serum.
One modification was to increase time of incubations of reactants
with second antibody from 1 to 24 hr. In addition, the range of con-
centrations in the standard curve was from 5 to 160 ng/tube, because
this range encompassed concentrations of T4 expected in bovine serum.

when possible, all samples collected from an experiment were
analyzed within a single assay. When this was not possible, an assay
consisted of serum samples from those bulls which were initially
paired by body weight for assignment to light treatments. Hormone
concentrations from previous studies were used to estimate expected
hormone concentrations and to allow selection of two different dilu-
tions of serum which would be quantified on the portion of the standard
curve with the steepest slope. The coefficients of variation within

and between assays were estimated by inclusion of a series of dilutions

35

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m.nH H.ma Aammav orms cameos am . rms - er o.oH . «.0 rue
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mhsemoomsssaoausmuu.a canes

36

of serum from a standard pool of bovine sera.

 

E. Objectives and EXperimental Design

 

Experiment 1.. Duration of Light

I This study was designed to evaluate the effects of an abrupt
increase from 8 hr of light per day'to either 16 or'20 hr of light per
24 hr day on concentrations of Prl, CH, TSH, glucocorticoids, T4 and
insulin in sera from prepubertal bulls.

Prior to the start of this experiment, two groups of four bulls
each, 5 to 18 wk of age, had been exposed to natural daylongths which
were 11.8 hr on November 1 when bulls were housed in the chambers. ‘
Following a 2 wk adaptation to the environmental chamber (8L316D photo-
periods), bulls were exposed to 8 hr (0700 to 1500 hr) of "cool white”
fluorescent lighting (General Electric Co.) each day for 6 wk. At the
end of 6 wk, photoperiods were lengthened, one group receiving 16 hr
(0300 to 1900 hr) and the other group 20 hr (0100 to 2100 hr) of light
daily for an additional 8 wk. Light intensity was maintained at 650
lux, ambient temperature averaged 21 C, and relative humidity averaged
60% for the duration of the study.

-Bulls were bled twice each week at 1100 hr as outlined in section
C, Blood Sampling Procedures, and hormones were monitored for changes
in concentrations coincident with changes in body growth or photo-
period. All serum samples were assayed for Prl, CH and TSH. In
addition, insulin, T4 and glucocorticoids were quantified in samples
collected during wk 5 and 6, 8 and 9, and 11 and 12. These intervals

correspond to 6 wk of exposure to 8L316D photoperiods, 2 to 3 wk of

37

exposure to 16L38D or 20Lr4D photoperiods and 5 to 6 wk exposure t0'
16L38D or 20Lr4D photoperiods.

Photoperiods were compared for the ability of the pituitary to
release Prl, CH and TSH following injection of a standard quantity of
TRH. Bulls were challenged with TRH (33 pg/lOO kg body weight) after
6 wk of daily exposure to 8 hr of light and 3 and 6 wk after daily
exposure to light was increased to 16 or 20 hr. Collection of blood
before each TRH challenge began at 0945 hr. Relative to time of TRH
injection, blood was sampled at -30, -15, —5, 0, 4, 6, 8, 10, 12, 14,
16, 20 and 30 minutes for analysis of Prl concentrations in sera.
Samples collected at -15, 0, 6, 10, 14, 20 and 30 minutes were assayed'
for CH and TSH concentrations.

Three days after the TRH challenges during wk 6 and 12 metabolic
clearance rates (HCR) of Prl were determined. Polyvinyl cannulas were
inserted in both jugular veins of the bulls. Blood was drawn from one
cannula while NIH-B4 Prl dissolved in O.D% bovine serum albumin-0.85%
saline was infused through the other cannula at 0.50 mg Prl/100 kg
body weight per hr. Blood was collected at 0900 hr (30 min prior to
the start of the infusion) and at 30. 90. 105. 120. 135, 150, 165, 180,
195 and 210 min after the start of infusion. In previous studies 60
to 120 min were required for Prl to reach steadybstate (Tucker et al.,
1973): a condition in which the rate of Prl infused equals the rate at
which it is cleared (Tait, 1963). In my studies, steady-state concen—
trations of Prl were achieved in all bulls within 120 min. Pro-infusion
Prl concentrations were subtracted from concentrations of Prl in samples

collected at 15 min intervals after 120 min. These values were divided

38

into the rate of infusion of Prl to provide estimates of NOR. At 210
min infusion was stopped and blood samples were collected at 5 min
intervals for 30 min. Disappearance rates, the time for clearance of
half the concentration of Prl from the serum (Té), were calculated from
the slope of log Prl concentrations over time.

Experiment 2. Intensity of Light

This study was designed to establish the effects of light
intensity on concentrations of Prl, CH, glucocorticoids and T4 in sera
'from prepubertal bulls.

Prior to the start of this experiment, eight bulls had been
‘exposed to natural daylength which was 10.4 hr on February 10 when
bulls were housed in an environmental chamber at 19 C with relative
humidity at 69% and a 16L38D photoperiod (0600 to 2200 hr). One group
of four calves was exposed for 6 wk to 22 lux while a second group of
four calves received 540 lux of "cool white" fluorescent lighting. At
wk 7, bulls were switched to the alternate intensity and maintained
an additional 6 wk.

At the end of 12 wk of exposure to 16 hr of light, length of
light exposure was decreased abruptly to 8 hr and bulls were maintained
for an additional 3 wk.

Bulls were bled twice weekly at 1400 hr throughout the experiment,
as outlined in section 0.. Blood Sampling Procedures. Sera collected
'during the first 12 wk were assayed for Prl and CH3 however, sera
collected after photoperiods were decreased from 16L38D to 8L316D*were
assayed for Prl only. Samples collected twice weekly by venipuncture
between wk 4 through 6 and between wk 10 through 12 were assayed for

T4 and glucocorticoid concentrations.

39

Light intensities were compared for the ability of the pituitary
to release Prl and CH following injection of a standard concentration
of TRH. Bulls were injected with TRH at the end of each 6 wk.
Collection of blood before TRH challenge began at 1100 hr. Blood
samples were collected and sera assayed for Prl and CH as described in
Experiment 1.

Experiment 3,, Wavelength of Light

This experiment was designed to show the effects of wavelength
of light on concentrations of Prl, CH, glucocorticoids, T4 and LH in
sera from prepubertal bulls.

Prior to the start of this experiment, eight bulls had been
- exposed to natural daylengths which were 15.3 hr on June 26 when bulls
were housed in an environmental chamber at 21 C with relative humidity
at 69%. .Following a 6 day adaptation to the environmental chamber
(8le D photoperiod), all calves were exposed to 8Lal6D photoperiods
(1000 to 1800 hr) with 5&0 lux of "cool white” fluorescent light for.
the first 5 wk of the experiment. At the end of this time, one group
of bulls received 8 additional hr (1740 to 0140 hr) of red fluorescent
light (General Electric, 550 to 750 nm), while the other group received
8 additional hr (1740 to 0140 hr) of blue fluorescent light (General
Electric, 300 to 425 nm) for a total of 16 hr of light per day. The
total irradiance of the red and blue lights between 300 and 800 nm was
determined with a radiospectrophotometer, and red and blue lights were
adjusted to give an energy output of 41 pit/cm2 (Bickford and Dunn,
1972. C. 5). After 5 wk supplemental lighting was discontinued, and

bulls again received only 8 hr (1000 to 1800 hr) of "cool white" light

40

per day for the remaining 5 wk.
Bulls were bled twice weekly at 1400 hr, as outlined in section

0., Blood Sampling Procedures, and sera were analyzed for Prl and CH.
Clucocorticoids and T4 concentrations in sera were assayed from samples
collected between wk 4 to 5, 9 to 10, or 14 to 15. Calves were
injected with TRH on the 5th day of wk 5, 10 and 15. These experiments
started at 1145 hr on wk 5 and 10, and at 1330 hr on wk 15. Blood was
' collected and sera were assayed for Prl and CH as described in
EXperiment 1.

Variation of concentrations of LH in serum were studied from
samples collected on the last day of each 5 wk. Blood was sampled
(5 to 6 ml) from each bull at 10-min intervals between 1030 and 1720
hr (”cool white" light exposure was 1000 to 1800 hr) in wk 5 and 15,
and from 1030 to 0100 hr ("cool white" light exposure was 1000 to 1800
‘ hr: red or blue light exposure was 1740 to 0140 hr) on wk 10. In
addition, assays for Prl and CH concentrations were performed on sam-
ples which were collected at 30-min intervals starting at 1030 and

1040 hr, respectively.

F. Statistical Methods
Statistical analyses were calculated by a CDC 6500 computer and
programs in SPSS (Vogelbeck Computing Center, Northwestern university)
and STAT‘4 (MSU Computing Center, Michigan State university).
In Experiments 1 and 3, a sequence of light exposures made up a
treatment. Eor example, in ExPeriment 1, one treatment consisted of a

sequence of light exposures which increased from 8Lxl6D (period 1) to

41

'16L38D (period 2), while in a second treatment light exposures increased
from 8L316D to 20Lt4D. Similarly, in Experiment 3, treatments consisted
of sequences of light exposures which went from 8L316D (cool white;
period 1) to l6La8D (8 hr cool white plus 8 hr red ore hr cool white
plus 8 hr blue; period 2) and returned to 8L:16D (cool whiteg'pcriod 3).
In Experiments 1 and 3, hormone concentrations during-8le6D were

compared with concentrations during 16L38D photoperiods, therefore each
bull served as his own control. Split-plot analysis of variance was
used to partition the proportions of variance due to treatments, bulls
within treatments, periods (interval of exposure to a duration or wave-
length of light), and sampling intervals within periods. Estimates of
»standard errors obtained from the appropriate'mean square error (MSE)
terms of this model were used to test differences among overall means.
.EXperiment 2 was handled in a similar manner; however, all bulls
received 22 and 540 lux of light in a crossover experiment. Therefore,
parameters included in the split—plot analysis of variance included
’treatment (intensity), bulls, interval of exposure to an intensity
(periods) and sampling interval within periods.

A Variances associated with some hormones, usually Prl, were heter-
ogeneous. That is, differences in treatment means were large, and
variances seemed to increase with increased magnitude of the means.
Therefore, all parameters in the split-plot analysis of variance which
ehad highly significant F ratios when tested with the ordinary error
.term, were tested with the conservative tabular F of Ceisser and
Greenhouse as suggested by Gill and Hafs (1971). when E ratios were

significant (pi< 0.05) for the conservative procedure, tests adapted

42

for heterogeneous variance were used to make specific comparisons of
treatment means (Gill, 1971; Gill, 1977) and standard errors of means
were calculated from the sample variance (s2) within each treatment.

In EXperiment l, regression methods were used to determine rate
of increases of concentrations of Prl with increase of daily light (0.35
exposure from 8 to 16 or 20 hr. Use of ng/ml values of Prl resulted
in large coefficients of variation (55 to 94%) and small correlation
between increases in Prl after increase in daily light exposure (0.35
to 0.51). Transformation of data to logarithmic values alleviated
this problem. In all experiments, feed intake (kg) and heart girth
(cm) were regressed on days within a period of light exposure. Slopes
of these regressions were contrasted (Student's t-test) to estimate the
effects of light exposure on feed consumption and growth.

In all studies, several measures were used to describe Prl and
CH responses after injection of’TRH. First, greatest concentration of
a hormone between 4 and 30 min after bulls were injected with TRH was
recorded as ”peak" concentration. Peak concentration and the time to
reach this peak were analyzed by analysis of variance. The second
measure used was the area under the hormone response curve (Vines,
et al., 1976). Average baseline concentrations (mg/ml) of Prl and CH
were calculated for each bull at each TRH trial. This value was sub-
tracted from Prl or CH concentrations measured between 4 and 30 min
after'TRH, and a third degree least squares polynomial curve was com-
puted on adjusted hormone data (ng/ml) plotted against time (min).
The area under this curve was calculated by integration, and the final

1

values, ng ml” min, were analyzed with analysis of variance. In

43

addition, disappearance rates (T%) of Prl and CH after TRH were calcu—
lated on individual bulls by regression of log hormone concentration on

time. Slopes obtained were analyzed by analysis of variance.

RESULTS

Experiment 1. Duration of Light

A. Prolactin

 

Concentrations of Prl in sera collected twice weekly by venipunc-
ture averaged 9.3 and 5.91: 2.8 ng/ml (p) 0.10) in two groups of four
bulls during 6 wk of exposure to 8 hr of light per day (Figure 1).
within 7 days after hours of light were increased from 8 to 16 or from
8 to 20 hr, concentrations of Prl increased an average of 113%

(p'< 0.05, Table 2). Concentrations of Prl in sera of bulls averaged
66.8 and 55.8 1 6.2 ng/ml (p:> 0.10) during the last 5 wk of exposure
to 16 or 20 hr of light per day (Figure 1).

Following 6 wk of exposure to 8 hr of light daily, the rate of
increase of Prl during 8 wk of exposure to 16 or 20 hr of light per day
was described best by linear regression of log Prl concentration
(Table 3). Rate of increase of log Prl concentration was 0.02 ng/ml
per day of exposure to 16 or 20 hr of light for the duration of the 8 wk.

Concentrations of Prl in serum collected twice weekly by veni-
puncture averaged 1.8 times greater (pi< 0.01) than concentrations in
samples collected via cannulas prior to TRH challenges during wk 6
(8le6D photoperiod), 9 (16L38D or 20Li4D photoperiods) and 12 (16L38D
or 20Ls4D photoperiods) (Table 4). However, concentrations of Prl in

samples collected by venipuncture versus cannulas were not significantly

u.

45

Figure l.--Prolactin (Prl) in serum from prepubertal bulls
during daily light exposure which was increased
from 8 to 16 hr (H) or from 8 to 20 hr (Cu-0).
(four bulls per treatment)

PROLACTIN (ng/ml SERUM)

 

46

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70- XX
x—x 8hr light increased 10 IS hr
0---0 8hr light increased to 20hr " \\
60- 9 ' \
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4?

Table 2.--Dunnett analysis of prolactin (Prl) concentrations 4 to 18

days after increase of daily light from 8 to 16 or 20 hr.

 

 

.Dgys after incrggse in light

 

 

 

Observation 0 4 7 ll 14 18
Prl (ng/ml) 5.3 6.2 11.3 13.3 16.u 23.0
Increase" - 0.9 6.0* 8.0* 11.1* 17.7%
14511" - 1.7 5.1» 7.1+ 9.8 10.0
aIncrease above 5.3 ng/ml which was the concentration of Prl on last

day of 8le6D photoperiod.

‘01131) is minimum significant difference (a - 0.05); increases in con-
centration of Prl which exceed MSD are significantly greater than

zero and

are followed by *.

Table 3.--Linear regression of log prolactin (Prl) concentration

on days after increase of daily light from 8 to 16 or
20 hr.

 

 

 

Light Intercept Slope Coefficient r2
of geriation Cllg
16 0.95 i .06 0.020 1 .002 17.2 0.6+
20 0.73 :t .06 0.022 :t .002 20.0 A 0.66

 

48

Table 4.--Prolactin (Prl) concentrations in serum
collected by venipuncture or cannulation
after daily exposure of bulls to 8, 16 or
20 hr of light.

 

 

 

 

Light Prl M11

(hr) Weeks Venipuncture Cannulation
8 6 6.1 6.4
16 - 20 33 27.0 8.3
16 - 20 6b 44.6 27.9
Meanc 25.9 14.2
$2 3.3 1.8

 

“wk 9 of experiment. bflk 12 of experiment.

cMean Prl (mg/ml) less (p'< 0.05) in samples
collected through cannulas than by venipuncture.

49

Figure 2.--Effect of weeks of exposure of bulls to 8Lrl6D or
161.3811 and 201mm photoperiods on prolactin (Prl) in
serum after injection of thyrotropin releasing hormone
(TRH). (eight bulls per treatment) Standard errors
of means for Prl collected prior to TRH {-30 to 0 min)
or at intervals immediately after TRH corresponding to
maximal concentrations (4 to 10 min) or disappearance
of Prl (12 to 30 min), appear above response curves.

50

 

 

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MINUTES

51

different (p) 0.10) when daily light exposure was 8 hr. After 3 wk
of exposure to 16L38D or 20Lr4D photoperiods, concentrations of Prl in
samples collected by cannulas were 30% of concentrations obtained by
venipuncture. Furthermore, concentrations of Prl in samples collected
through cannulas continued to increase to 60% of concentrations obtained
by venipuncture after 6 wk of exposure to 16L38D or 20Lr4D photoperiods.

Increases in concentrations of Prl after'TRH injection were not
different (p:> 0.10) between groups of bulls exposed to 16 or 20 hr of
light daily. Therefore, data from the groups were combined in Figure
2. Concentrations of Prl in serum collected prior to TRH injection
were 5.9 1.2.2 ng/ml after bulls had been exposed to 6 wk of 8Lr16D
photoperiods and increased (p < 0.05) to 9.9 :i: 2.7 ng/ml after 3 wk of
daily exposure to 16 or 20 hr of light. After 6 wk of exposure to 16
or 20 hr of light per day, concentrations of Prl increased again
(P'< 0.05) to 33.2 i 12.8 ng/ml. Maximal concentrations of Prl after
injection of TRH increased (p < 0.01) 3- and 8—fold after photoperiods
were increased from 8 to 16 or 20 hr of light daily for 3 and 6 wk,
respectively (Table 5). In addition, the quantities of Prl released
after injection of TRH at 3 and 6 wk after exposure to 16 and 20 hr of
light, as measured by area under the hormone response curve, were
increased (pi< 0.05) 3- and 8.5-fold over values obtained after 6 wk
exposure to 8L316D photoperiods (Table 5).

Despite the influence of duration of photoperiod on release of
Prl after injection of TRH, time to maximal Prl concentration after'TRH
averaged 7.3. 7.0 and 6.5 1 0.8 min (p> 0.10) when daily light exposure

was 8 hr and after daily light exposure had increased to 16 to 20 hr

52

Table 5.--Prolactin (Prl) released to thyrotropin releasing hornone (TRH)
after daily exposure of bulls to 8 or 16 to 20 hr of light,

 

 

 

 

Prl response _7
Light Concentration (nanll Area Time of
__(hr) Heeks Prior'to TRHc Peakc {pg 101'”1 nin)°dgjggkz(nin)_
8 6 5.9 1 2.2 35.0 i 9.3 370 :I: 160 7.3 :t 0.8

16 - 20 3‘ 9.9 :t 2.7 82.9 i 1h? 1099 i 192 7.0 :l: 0.8
16 - 20 61) 33.2 :t 12.8 226.0 :I: 2n.0 3101» :l: 606 6.5 :t 0.8

 

a‘Hk 9 of experiment. bUk 12 of experiment.

cMeans (1 SE) increased after 3 wk exposure to 16 to 20 hr of light
(p < 0.05) were further increased (p < 0.05) after an additional 3 wk
exposure to 16 to 20 hr of light per day.

dng ml'1 min is the integration of Prl concentration in each bull from
1+ to 30 nin after TRH minus average baseline concentrations collected
prior to TRH (area under response curve).

Table '6.--Rate of metabolic clearance of prolactin (Prl)
after 6 wk of daily exposure of bulls to 8, 16
or 20 hr of light.

 

1 _—
-'__ r

Light Clearance rate Disappearance rate

 

Lhr) buying)“ lain)a

8 720 :I: 90 31 i 8
16 #73 :t 127 58 i 45
20 635 :I: 33 327 i 281

 

aMeans (1 SE) after 6 wk exposure to 16 or 20 hr not
different (p> 0.10) from neans (1: SE) after 6 wk
exposure to 8 hr of light daily.

53

for 3 and 6 wk (Table 5). Sinilarly, disappearance rates (T%) of n.0,
36.5 and 33.5 1 9.1 min (p> 0.10) occurred after maximal concentra-

.- tions of Prl to injection of TRH after bulls were eXposed to 6 wk of
8L116D and to 3 and 6 wk of 16L38D or ZOLth Photoperiods. Six weeks
of daily exposure to 8, 16, or 20 hr of light did not affect (p> 0.10)
netabolic clearance rates or disappearance rates (Ti) of infused Prl
(Table 6).

B. Growth Hormone

Concentrations of CH in sera collected twice weekly by venipunc-
ture froa bulls exposed to 8 to 16 hr,or 8 to 20 hr light treatments
for 13 wk averaged 9.2 and 10.9 :t 2.5 rig/ml (p> 0.10). respectively
(Figure 3). Serum CH concentrations ranged between 8.3 to 11.7 ng/ml
(p > 0.10) after photoperiods were increased from 8Lsel6D to 16L38D or
to 20LuhD. However, CH concentrations were less variable in bulls
exposed to 8L.16n (s?- - 30.8) than in bulls exposed to 161.181) or 201nm:
(s2 - 2h2.2) photoperiods (p‘< 0.10). Serum CH in samples collected by
venipuncture and cannulation were not different (p> 0.10), averaging
12.7 and 13.9 :I: 2.2 ng/ml (Table 7). '

Mean concentrations of serum CH prior to TRH ranged between 12.7
and 15.8 i 2.7 ng/ml (p > 0.10; Table 8). Concentrations of an increased
to peak values of 311.1; to 58.7 :1: 114.2 ng/nl (p < 0.01). within 11.5 to
13.5 min after injection of’TRH, but none of these measures of response
to TRH was affected (p > 0.10) by increasing photoperiod from 8Lcl6D to
16L18D or 20L11+D (Table 8). Furthermore, CH response to TRH as measured
by area under the curve was not changed (p > 0.10) by increase in length

of daily exposure to light (Table 8). In this study, rates of CH

5h

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Table 7.--Crowth hormone (CH) concentrations in serum
‘ collected by venipuncture or cannulation
after daily exposure of bulls to 8, 16 or
20 hr of light.

 

 

T

Light on (gal)

 

 

 

(hr) Heeks Venipuncture Cannulation
3 6 9.“ 12.7
16 - 20 3a 17.2 > 15.8
16 - 20 6b 11.11 13.1
Mean‘3 12.7 13.9
SE 2.2 2.2
ailk 9 of experiment. bilk 12 of experiment.

cHean concentration of CH in samples collected
through cannulas not different from samples
collected by venipuncture (p > 0.10).

Table 8.--Crowth hormone (CH) released to thyrotropin releasing hormone
(TRH) after daily exposure of bulls to 8 or 16 to 20 hr of

 

 

 

 

light.
CH response r
Light Concentgalion Md) Area Time of
(hrL Weeks Prior to TRH° Peakc (ng ml"1 min)eel peak (ninlc
' 8 6 12.7 :I: 2.7 39.9 :1: 114.2 335 :t 257 11.5 :t 1.3
16 - 20 3" 15.8 :I: 2.7 58.7 1 115.2 818 :l: 257 13.5 i 1.3
16 - 20 6" 13.1 :1: 2.7 116.6 :1: 111.2 532 :t 257 13.0 :t 1.3
aHk 9 of experiment. bflk 12 of experiment.

c:Heans (:1: SE) after 3 and 6 wk of 16 or 20 hr not different (p> 0.10)
from means (1 an) after 6 wk of 8 hr of light daily.

dng 1.1-1 min is the integration of on concentration in each bull from
1+ to 30 min after TRH minus average baseline concentrations collected
prior to TRH (area under response curve).

56

disappearance between 12 and 30 min after TRH averaged 23, 25 and
33 :t #3 min (p> 0.10) in samples collected during wk 6 (8le611) and
wk 9 and 12 (16L18D or 20LshD).
C. Thyrotropin

‘ Concentrations of TSH in sera collected twice weekly by venipunc-
ture were 3.2 and 3.7 :t 1.7 ng/ml (p> 0.10) in two groups of bulls
exposed to daily light which increased from 8 to 16 hr or from 8 to 20
hr per day (Figure 4). Concentrations of TSH in sera from bulls
declined (p«< 0.05) from “.2 ng during the first 2 wk of the experiment
to 3.5 ng/ml after 6 wk of exposure to 8Lil6D and to 3.2 ng/ml after
6 wk of exposure to 16L38D or 20LauD photoperiods.

Injection of TRH during wk 6 (8L316D) and wk 9 and 12 (16mm) or

20LihD) increased serum TSH concentrat ions an average of 1+.8-fold
(p‘< 0.05). However, neither peak concentration of TSH nor time to peak
concentration after TRH was changed (p > 0.10) by increase in hours of
daily light exposure (Table 9).

D. Other Hormones

 

Average concentrations of insulin, glucocorticoid and T1, were not
different (p> 0.10) between groups of bulls subjected to daily light
exposures which were increased from 8 to 16 hr or from 8 to 20 hr.
Therefore, data from the 8 to l6,and 8 to 20 groups were combined in
Table 10.

Increase in number of hours of light per day did not affect
insulin concentrations (p > 0.10); average values ranged between 2.3
to 2.5 lie/m1.

Clucocorticoids decreased (p < 0.05) from 2.8 ng/ml after 6 wk of

57

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58

Table 9.-4Thyrotropin (TSH) released to thyrotropin releasing hor-
mone (TRH) after daily exposure of bulls to 8 or 16 to
20 hr Of light.

 

.1 t
fi‘

 

 

 

 

TSH response
Light , Concentration(ng[ml) Time of peak
#(hrl weeks Prior to mac Peakc (pin)c
8 ‘ 6 309 1 103 1703 i 700 600 i 903
16 - 20 3a 3.11 :t 1.3 16.0 1 7.0 8.0 :t 9.3
16 - 20 61) 3.3 i 1.3 18.1 :t 7.0 15.0 i 9.3

 

aflk 9 of experiment.
ka 12 of experiment.

°heans (:t SE) after 3 and 6 wk of 16 or 20 hr not different (p> 0.10)
from means (t SE) after 6 wk of 8 hr of light daily.

59

daily exposure to 8 hr of light to 1.8 ng/ml after 3 wk of daily .
exposure to 16 or 20 hr of light. Continued exposure to 16 or 20 hr
of light per day did not result in additional decreases in glucocorti-
coids (p5 0.10) (Table .10).

After 3 wk of exposure to 16L18D or 20L1UD, serum Tu increased
1.2-fold (p < 0.05) above concentrations observed at the end of 6 wk
of exposure to 8Lil6D photoperiods. However, Th concentrations did not
continue to increase during the second 3 wk of exposure to 16L38D or
20le+D photoperiods. ‘

E. Feed Intake and Body Growth

Feed intake for 24 hr per group of bulls increased from 11 to 29
kg in one group and from 12 to 210 kg in the other. However, rate of
feed intake within each 6 wk did not change when photoperiods were
increased from 8le6D to 16L18D or from 8le6D to 20L14D (p > 0.10;
Table 11). Similarly, rates of increase in feed consumption between
groups of bulls were not different when photoperiods were 8le6D (0.116
vs 0.81 kg per 3.5 days), nor were they different when photoperiods were
16L18D' or 8L120D (0.51 vs. 0.31; kg per 3.5 days).

within one group of bulls, heartgirth increased from 98 to 108 cm
at a rate of 0.85 cm and from 109 to 119 cm at a rate of 0.96 on between
twice-weekly measurements (p > 0.10) during 6 wk of exposure to 8Lil6D
I and 16L18D photoperiods, respectively (Table 11). Heartgirths of the
second group of bulls increased from 911 to 102 cm at a rate of 1.16 on
per interval between measurements during 6 wk of exposure to 8 hr of
light daily, and from 10“ to 114 cm at 1.00 on per interval during 6 wk
of 20le$D photoperiods (p> 0.10). Rates of change in heartgirth were

60

Table 10.--Insulin, glucocorticoid and thyroxine (Th) in
serum after daily exposure of bulls to 8 or
16 to 20 hr of light.

I _ _—

 

 

 

Light Hormone ing/m1)

(hr) Weeks Insulin Clucocort ico id Ta
8 6 2.3 2.8° 56.u°
16 - 20 315L 2.5 1.8‘1 67.3(1
16 - 20 6b 2.3 Lad 69.7ed
Mean 2.11 2.0 62.8
SE 0.3 0.2 2.2
a'ilk 9 of experiment. ka 12 of experiment.
c,d

In each column, means with different superscripts are
significantly different (p < 0.05).

Table 11.--Increase in 211 hr feed consumption and heartgirth
measured twice-weekly during daily exposure of bulls
to 8, 16 or 20 hr of light.

 

 

 

L j:—

 

 

 

 

Light Increase per 3. 5 days
(hr) Weeks Feed intake (kg)° Heartgirth (cm)°
H163 1-6 0,146 :I: 0.16 0.85 i 0.65
7'12 0.51 i 0.21 0.96 i 0.66
8—>2ob ' 1-6 0.81 :l; 0.23 1.16 i 0.02
7-12 0.3“ i 0.12 1.00 i 0.38

 

a'Photoperiods of four bulls increased from 8Lil6D (wk 1-6) to
161.181) (wk 7-12).

bPhotoperiods of four bulls increased from 8L116D (wk 1-6) to
201.040 (wk 7-12).

cAverage increase (:1: SE) during 6 wk of exposure of bulls to
16 or 20 hr did not differ (p> 0.10) from increase during
6 wk exposure to 8 hr of light daily.

61

not different between the groups of bulls during 6 wk exposure to 8, 16

or 20 hr of light per day.
Experiment 2 . Intensity of Light

A. Prolactin

Concentrations of Prl in sera collected twice-weekly by venipunc-
ture averaged 48.1 and 63.2 :t 5.8 ng/ml (p> 0.10) in eight bulls during
exposure to 16L38D photoperiods at light intensities of 22 or 500 lux,
respectively (Figure 5). Four bulls received 22 lux of light during
wk 1 to 6, followed by 6 wk of 540 lux. The other four bulls received
the opposite sequence of light intensity. Sequence of exposure to light
intensities may have been important, because concentrations of Prl
increased 1.5 times (p 30.05) in serum of bulls which were exposed to

6 wk of 22 lux of light after initial exposure of 6 wk of 22 lux. In

‘ contrast, concentrations of Prl in sera from bulls which received 6 wk

of 540 lux followed by 6 wk of 22 lux of light averaged 44.8 and 41.8
ng/ml (p> 0.10), respectively.

After 12 wk of exposure to 16L18D, photoperiods were decreased to
8L316D and animals were maintained at either 22 or 540 lux for an addi-
tional 3 wk (Figure 5).. Concentrations of Prl from sera collected twice
weekly were not decreased (p > 0.10) 3 wk after exposure to decreased
length oftu light.

I Concentrations of Prl in sera collected through cannulas at ~30
and 0 min prior to TRH challenges on wk 6 and 12 were 60% less (p < 0.01)
than Prl concentrations in two samples of sera collected by venipuncture

during those weeks (Table 12).

I60[

I40 I“

80*

60*

DROLACTIN (ng/ml SERUM)

40'

2C"

 

 

62

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-—-540|ux

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Figure 5.--Prolactin (Prl) in serum from prepubertal bulls during

daily exposure to 16 hr of 22 (---) or 540 (—) lux of
light. (four bulls per intensity within each 6 wk
interval).

63

Table 12.--Prolactin (Prl) concentrations in serum
collected by venipuncture or cannulation
after daily exposure of bulls to 16 hr
of 22 or 540 lux of light.

 

 

 

 

Light Prl_(gg/ml)
41mg) week Venippncture Cannuljat ion

22 6 63.4 _ 38.3

12 44.8 13.2

500 6 83.6 29.6
12 73.3 25.2

Meanat -- 66.3 26.6
s: -- 8.1 8.1

 

a’llean Prl (ng/ml) less (p«< 0.01) in samples col-
lected through cannulas than by venipuncture.

64

Prior to TRH challenges, concentrations of Prl in sera averaged
(wk 6 and 12 combined) 23.0 and 25.1 :t 7.6 ng/ml (p> 0.10) in bulls
exposed to 22 and 540 lux, respectively (Figure 6: Table 13). Injec-
tion of TRH increased (p'< 0.01) Prl concentrations over basal concen-
trations (Figure 6); however, light intensity did not influence this
response if results of wk 6 are combined with results of wk 12. As with
concentrations of Prl in sera collected twice weekly by venipuncture,
sequence of light intensity may have been important, because during
wk 7 to 12 bulls exposed to 540 lux of light had 187% greater (p < 0.05.)
peak concentrations of Prl and 167% greater (p g 0.05) area under Prl
response curve (Table 13) than bulls exposed to 22 lux of light. In
contrast, peak concentrations and areas under response curves for Prl
after TRH did not differ (p> 0.10) between groups of bulls exposed to
540 and 22 lux of light during wk 1 to 6 (Table 13).

Maximal concentrations of Prl occurred 5.5 and 5.3 1 0.9 min
(p > 0.10) after injection of TRH when intensities of light were 22 and
500 lux, respectively (Table 13). Similarly, disappearance rates (T43)
of 61.8 and 102.9 1 67.7 min (p> 0.10) occurred after maximal concen-
trations of Prl to injections of TRH when light exposures were 22 and
540 lux.

B. Growth Hormone

 

Basal concentrations of CH in sera collected from bulls eXposed
to 22 or 540 lux of light averaged 10.6 and 13.6 i 1.5 ns/nl (p> 0.10.
Figure 7). Concentrations of CH were more variable (p < 0.01) in bulls
exposed to 540 lux (s2 - 321.8) than in bulls exposed to 22 lux of light

(32 - 79.4). However, collection of blood by venipuncture or through

65

Figure 6.--Effect of intensity of light exposure on prolactin
(Prl) in serum after injection of thyrotropin
releasing hormone (TRH) in bulls exposed to 16 hr
of light per day. (four bulls per intensity within

each 6 wk interval)

PROLACTIN(ng/ml SERUM)

220
200
l 80
I 60
I 40
I 20
IOO
80
60
4O
20

66

I

e Week 6

L.

0—--o 22lux
PH54O|ux

W

I I
<—

I

 

J l Illllll L l

 

L.

_

 

Week I2

x--—x 22 lux

 

I l lllllll l

 

~30 -|5 -50 IO 20 30

-30

MINUTES

-I5 -

50 IO 20 3O

67

Table 13.--Prolactin (Prl) released to thyrotropin releasing hormone
(TRH) after daily exposure of bulls to 16 hr of 22 or 540

 

 

 

 

 

 

lux of light.
Prl response .
Light (nglml); Area Time of peak
(lux) Heek Prior to TRH“ Peak (ng ml"1 min)b (min)3
22 ' 6 33.2 98.1c 998° 6.0
12 12.8 113.0c 1391" 5.0
500 6 22.4 90.20 764c 4.5
12 27.9 211.3‘1 2326‘1 6.0
“can '"" 2a. 1 128.2 1370 5 .4-
31: -- 7.6 15.1 313 0.9

 

‘heans (i as) not different (p> 0.10).
bng ml'1 min is the integration of Prl concentration in each bull from
4 to 30 min after TRH minus average baseline concentrations collected
prior to TRH (area under response curve).

c'dlzeak mean; with different superscripts are significantly different
p< 0.05 .

érea mean; with different superscripts are significantly different
P30fi5.

68

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70

cannulas did not affect (p> 0.10) estimates of basal CH concentrations,
which averaged 8.8 and 7.5 :I: 0.7 ng/ml (Table 14).

Prior to TRH challenges, CH concentrations in sera averaged
(wk 6 and 12 combined) 7.1+ and 7.7 i 2.1 ng/ml (p> 0.10) in bulls
exposed to 22 or 540 lux (Table 15). Injection of TRH increased CH
more than 4-fold (p < 0.01). Peak concentrations averaged 36.8 and
27.7 :I: 4.3 ng/ml, but were not different (p> 0.10) between bulls
exposed to 22 or 540 lux (Table 15). Light intensities of 22 and 540
lux did not differ (p> 0.10) in their effect on area under the CH
response curve, which averaged 490 and 345 i 80 ng ml"1 min (Table 15).

After injections of TRH, maximal concentrations of CH occurred at
10.3 and 10.8 :t 0.7 min when light intensities were 22 and 540 lux
(Table 15). Disappearance rates (T-§:) of CH in bulls exposed to 22 or
540 lux of light averaged 51.9 and 26.1 :1: 16.0 min (p> 0.10).
C. Other Hormones

Average concentrations of glucocorticoid collected twice weekly
by venipuncture were between 1.2 and 1.8 :t 0.4 ng/ml but did not differ
(p > 0.10) between bulls exposed to 540 versus 22 lux of light (Table 16).
Similarly, concentrations of Ty, measured at 22 or 540 lux did notdiffer
(p < 0.10); averages were 77.3 and 78.4 :t 2.8 FIG/Ill (Table 16).
Q‘L Feed Intake jaInd Body Crowth

Feed intake per 24 hr in one group of four bulls increased from
12 to 25 kg at 1.17 kg per 3.5 days during 6 wk of exposure to 22 lux of
light and from 21 to 32 kg at 0.85 kg per 3.5 days during 6 wk of expo-
sure to 540 lux of light (p> 0.10: Table 17). In a second group of

bulls exposed to 6 wk of 540 lux of light, feed intake increased from

71

Table l4.-Crowth hormone (CH) concentrations in serum
collected by venipuncture or cannulation
after daily exposure of bulls to 16 hr of
22 or 540 lux of light.

 

 

 

Light _fi 68 L n1

(lux) Week Venipupcture Cann tion

22 6 7.8 6.8

12 14.1 8.0

540 6 9.8 9.1

12 3. 5 6.2

Mean‘ -- 8.8 7.5

SE '- 0e? 0.?

 

"Mean CH (mg/ml) in samples collected through
cannulas not different from samples collected by
venipuncture (p> 0.10).

72

Table l5.--Crowth hormone (CH) released to thyrotropin releasing hormone
(TRH) after daily exposure of bulls to 16 hr of 22 or 540 lux

 

 

 

 

 

of light.
, CH regponse
Light . (WIT) Area Time of peak
’ (lux) week Prior to TRH“ Peak“ (5 m1'1 nip)“ (min)al
22 6 6.8 38.7 616 11.5
12 8.0 34.9 365 9.0
500 6 9.1 31.11 387 10.0
12 6.2 24.0 304 11.5
Mean -- 7. 5 32 .2 418 10. 5
SE -- 2.1 4.3 80 0.7

 

aMeans (1 SE) after 6 wk of 22 lux not different (p> 0.10) from means

after 6 wk of 540 lux of light.

1’ng ml'1 min is the integration of CH concentration in each bull

from 4 to 30 min after TRH minus average baseline concentrations col-
lected prior to TRH (area under response curve).

73

Table l6.--Glucocorticoid and thyroxine (Tu) concen-
trations after daily exposure of bulls to
16 hr of 22 or 540 lux of light.

 

 

 

 

Light Hormone (gglml )

(lux) Week Clucocort icoida Ti,“
22 6 1.8 84.9
12 1.6 71.8
5140 6 1.7 69.7
12 1.2 84.8
Mean -- 1. 6 77.8
83 -- 0.4 2.8

 

‘neans (:1: 33) after 6 wk of 22 lux not different
(p> 0.10) from means after 6 wk of 540 lux of
light.

78

Table l7.--Increase in 24 hr feed consumption and heartgirth
measured twice-weekly during daily exposure of
bulls to 16 hr of 22 or 540 lux of light.

‘1 L
_ 1

 

 

Sequence
of Light , Increase per 3. 5 days
(lux) weeks Feed intakgg(kg)° Heartgirth_(cm)¢
22—r5lvoa 1-6 1.17 :l: 0.10 1.31 i; 0.28
7-12 0.85 :1: 0.13 1.28 :l: 0.30
540—» 22b 1-6 0.98 1 0.10 1.07 :I: 0.26
7-12 0.73 i 0.10 1.29 1 0.31

 

aLight intensities of four bulls increased from 22 lux
(wk 1-6) to 540 lux (wk 7-12).

bLight intensities of four bulls decreased from 540 lux
(wk 1-6) to 22 lux (wk 7-12).

cAverage increase (1 SE) during 6 wk of 22 lux not different
(p> 0.10) from increases during 6 wk of 540 luxs‘ average
increase during first 6 wk not different from increase during
2nd 6 wk.

75

11 to 23 kg at 0.98 kg per twice-weekly measurement: subsequent exposure
to 22 lux of light did not affect rate of. increase in feed intake

(p> 0.10; Table 17). Rate of increase in feed consumption did not
differ between the two groups of bulls (p> 0.10).

Heartgirths increased from 94 to 109 cm and from 109 to 124 cm
during 6 wk exposure of bulls to light intensities of 22 lux which were
increased to 540 lux; change in heartgirth was 1.31 and 1.28 cm between
twice weekly measm'ements, respectively (p> 0.10: Table 17). Similarly,
in bulls exposed to 6 wk of 540 lux which was decreased to 22 lux of
light, heartgirths increased from 94 to 106 and from 107 to 122 cm, but
rates of change (1.07 and 1.29 cm per 3.5 days) were not different
(p> 0.10). The two groups of bulls did not differ in the rate of

increase in heartgirth (p> 0.10).

aperiment 3. Waveleggth of Light

 

A. Prolactin

Within ‘5 wk after bulls were taken from natural environmental con-
ditions typical of June in East Lansing, MI and exposed to 8 hr of
"cool white” light per day, concentrations of Prl in sera collected
twice weekly by venipuncture decreased (p < 0.05) from 19.6 :t 1.8 to
10.4 :t 2.7 ng/ml (Figure 8). After daily light exposure was increased
to 16 hr by the addition of 8 hr of red (550 to 750 nm) or blue (300 to
425 nm) light to 8 hr of cool white light. concentrations of Prl
increased (p < 0.05) to 57.2 :I: 17.6 (red) and 37.5 :I: 13.4 (blue) ng/ml,
but did not differ from each other (p> 0.103 Figure 8). Five weeks

76

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after light exposure was decreased to 8L116D of "cool white" light, Prl
in serum again decreased (p‘< 0.05) to averages of 26.4 i:14.9 and

6.2 1.2.4 ng/ml (p:> 0.10) in bulls which had been exposed to red and
blue light, respectively.

Concentrations of Prl in samples collected by cannulation of bulls
were 50% lower than concentrations of Prl in samples collected by veni-
puncture during wk 5, 10 and 15 (p‘< 0.05: Table 18).

During the first 7 hr of light on the last day of wk 5. 10 and 15
estimates of basal concentrations of Prl were obtained from samples
collected through cannulas at half-hour intervals (Figure 9). Concen-
trations of Prl in sera from bulls exposed to 8 hr of white light plus
8 hr of red light averaged 15.7 i: 0.9 ng/nl and did not differ(p> 0.05)
from Prl concentrations in bulls exposed to 8 hr of white light plus 8
hr of blue light (18.3 1.1.3). Concentrations of Prl were greater
(p«< 0.01) during wk 10 when light exposure totalled 16 hr per day
(17.0 1 0.8 ng/ml) than during wk 5 or 15 when light exposure was 8 hr}
per day (wk 5 - 4.3 r 0.2 ng/nl and wk 15 - 5.5 :t 0.5 ng/ml). After
5 wk of daily exposure to 8 hr of "cool white" light during wk 5 con-
centrations of Prl were not different (p:> 0.10) from concentrations
during wk 15. Although basal concentrations of Prl were predominantly
lower during wk 5 and 15, occasionally (wk 15: 8L116D photoperiod)
concentrations of Prl were equal to or greater than average concentra-
tions in serum of bulls exposed to 16 hr of light per day. regardless of
wavelength of the supplemental 8 hr of light (Figure 10).

Concentrations of Prl in sera collected through cannulas prior to
injections of TRH on wk 5, 10 and 15 averaged 5.4 1.1.5, 14.6 1:2.2 and

8.0 1.3.1 ng/ml (Table 19). Concentrations of Prl were greatest

79

Table l8.--Prolactin (Prl) concentrations in serum collected from
bulls by venipuncture or cannulation after 5 wk of
daily exposure to 8, 16 or 8 hr of various wavelengths

 

 

 

 

 

of light.
Ligt Prl ( ml

(hr) (m1 Week Venipuncture Cannulat ion

8 300 - 750 5 10.7 5.4

16 550 - 750‘ 10 31.7 12.7

16 300 - 1.25" 10 30.4 16.7
I 8 1 300 - 750 15 14.8 7.8
Meanc 18.9 ' 9.3

SE < 2.9 1.1

 

"8 hr of 300 to 750 ml plus 8 hr of 550 to 750 nM (red).
‘08 hr of 300 to 750 nl plus 8 hr of 300 to 1.25 nM (blue).

cMean Prl (mg/ml) less (p < 0.01) in samples collected through
cannulas than by venipuncture.

80

Figure 9.—-Effect of wavelength and number of hours of daily
light exposure on prolactin (Prl) concentrations in
serum collected at 30 min intervals for 7 hr on the
last day'of wk 5, 10 or 15. (four bulls per treatment)

PROLACTIN (n9 / ml SERUM )

 

81

week 5
8 hr cool white

 

 

 

20h-
H)—
0 1
I I00 IBHOO ISHOO I700
week IO
8 hr cool white plus
. __ ,3 P 8hr redIXI or blue(0)
20 Mavnpm
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0 1 i 1 1 1 1 I l
IIOO IBOO ISOO I700
week IS
20,. 8 hr cool white
|0~ N‘/\
W‘xk31¢8fi§3«>o«>6
0 1 1

 

 

I I100 ISIOO I500 I700
HOURS

82

Figure lO.—-Effect of wavelength and number of hours of daily
light exposure on prolactin (Prl) concentrations
in serum collected at 30 min intervals from bull
601 on the last day of wk 5, 10 or 15.

33

 

 

 

 

BULL 60I
I. _ week 5
8 hr cool white
20 *-
. I-
lot-
0 . I 1 I I
; IIOO - I200 ‘ I300 I400 |500 l600 I700
05
LIJ BULL SCI
(1) week IO
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E __ 8hr red
\ 20
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85

(p < 0.01) during wk 10 when daily light exposure totalled 16 hr:
‘however, concentrations of Prl were not different (p:> 0.10) between
groups of bulls exposed to 8 hr of white light plus 8 hr of red
(16.7 :t 3.3 nix/.1) or 8 hr of blue light (12.5 :1: 3.0 ng/nl). sinilarly.
peak concentration of Prl released after TRH was greatest (p < 0.10)
‘ during wk 10 when daily light exposure totalled 16 hr; yet peak concen-
trations of Prl were not different (p > 0.10) between groups of bulls
exposed to 8 hr of white light plus 8 hr of red (108.0 1.15.6) or blue
(120.0 1'3“.8) light. Furtherlore. area of Prl concentrations for 30
min after TRH (week 10) did not differ (p> 0.10) between groups of '
bulls exposed to 8 hr of white light plus 8 hr of red (1855 1.238) or
blue (1915 1:706) light. However. area under the response curves were
greater (p < 0.01) during wk 10 than during wk 5 or 15 when daily light
exposure was only 8 hr (Table 19). Measure-ants of peak Prl concen-
trations and area of Prl concentrations after TRH tended to be greater
during wk 15 than during wk 5. g

1 Tine of naxiaal release of Prl after m (11.9 :1: 0.6 min) did not
differ (p > 0.10) between daily light exposure of 8 or 16 hr or betwaon
_groups of bulls exposed to 8 hr of white light plus 8 hr of red (“.0 nin)
or blue (11.5 win) light (Table 19). Similarly, disappearance rates
averaged 32.1 and 31.2 1 2.0 min (p> 0.10) in bulls exposed to 8 hr of
white light plus 8 hr of red or blue light.
B. Growth Hormone

Concentrations of GH in sera collected tron bulls twice weekly by

venipuncture averaged 10.“ 1:1.3 ng/il during 5 wk of daily exposure

to 8 hr of. “cool white” light (Figure 11). Increase in duration of

86

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88

daily light exposure from 8 to 16 hr by the addition of 8 hr of red

(550 to 750 nM) or blue (300 to 425 nh) light to 8 hr of "cool white"
-light did not affect (p:> 0.10) GH concentrations, which averaged

14.0 i;2.7 ng/hl (red light) and 10.9 1.0.8 ng/ml (blue light). However,
during the last 5 wk when light exposure had returned to 8 hr of "cool
white” light per day, concentrations of GH decreased (p<< 0.01) in both
groups of bulls to an average of 5.6 ng/ml (Figure 11).

Concentrations of GH in two samples collected by venipuncture did
not differ (p:> 0.10) from concentrations of GH in two samples collected
through cannulas prior to injections of TRH during wk 5. 10 and 15
‘ (Table 20).

Basal concentrations of CH were estimated from samples collected
at 30 min intervals for the first 7 hr of light on the last day of
wk 5, 10 and 15 (Figure 12). Average concentrations of CH as well as
sample variability were greater (p‘< 0.01) in samples collected on the
last day of wk 5 (8.1 ng/ml. s2 - 22.5. 8L116D) or 10 (9.1 ng/ml;

32 - 40.6; 16L18D) than in samples collected on the last day of wk 15
(5.8 ng/ml. 32 - 9.“, 8L116D). During wk 10, average concentrations of
CH were not different (P:> 0.10) between groups of bulls exposed to
16L38D phot0periods composed of 8 hr of white light plus 8 hr of red
(9.8 ng/ml) or 8 hr of blue (8.3 ng/ml) light. Figure 13 depicts con-
centrations of CH from a single bull sampled at 30 min intervals on the
last day of wk 5, 10 and 15. In this bull. as in most of the other
bulls studied. h- to 6-fold changes in concentrations of 0H occurred
among sanples collected on the last day during wk 5 (8L116D "cool white"
photoperiods) or wk 10 (16L18D photoperiods; 8 hr "cool white" plus 8

hr red or blue light); however, during wk 15 CH seldom exceeded 10 ng/nl.

89

Table 20.--Growth hornone (CH) concentrations in serum collected
from bulls by venipuncture or cannulation after 5 wk
of daily exposure to 8, 16 or 8 hr of various wave-

lengths of light .

 

 

 

 

 

Light ' GH (us/n1)
1hr) (ND Week Venipuncture Canngt ion
3 300 - 750 5 7.5 10.6
16 550 - 750‘ 10 11.8 17.0
16 300 - 1125b 10 30.2 18.1
8 300 - 750 15 6.0 h.“
weanc 11.5 10.8
SE 2.1 2.1

 

38 hr of 300 to 750 n! plus 8 hr of 550 to 750 nh (red).
b8 hr of 300 to 750 nM plus 8 hr of 300 to u25 nh (blue).

cMean 0H (ng/nl) in samples collected through cannulas not different
from samples collected by venipuncture (p> 0.10).

90

Figure 12.--Effect of wavelength and number of hours of daily
light exposure on growth hormone (GI-I) concentra-
tions in serum collected at 30 min intervals for
7 hr on the last da of wk 5, 10 or 15. (four
bulls per treatment

GROWTH HORMONE (ng/ml SERUM)

20

91

week 5
"' 8 hr cool white

1

 

1 360.588
0h!“ &

 

1 1 | 1 1 1
IIIO |3I0 |5|O |7I0

 

 

 

week I0
8 hr cool white plus
20 - 9‘ 8 hr redIXlor blue (0)
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10— ,' iii/{j
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IIIO |3|0 I5l|0 I7|O
weekl5
20— 8 hr cool white
'0 W his
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HOURS

Figure 13.--Effect of wavelength and number of hours of daily
light exposure on growth hormone (GH) concentrations
in serum collected at 30 min intervals from bull 601
on the last day of wk 5, 10 or 15.

GROWle HORMONE(ng/mlSERUM)

20

O

30

20

93

' BULL 60|
week 5
lllu cool whlle

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91.

Prior to injection of TRH, concentrations of GH in sera averaged
10.6 1 1.8. 17.6 :1; 5.1 and 11.11 i 0.8 ng/al in bulls sanpled in wk 5.
10 and 15 (Table 21). Concentrations of 011 were greater (p < 0.05)
during wk 10 (161.18D) than during wk 5 or 15 (8L116D) regardless of
whether bulls were exposed to 8 hr of ”cool white" supplemented by 8 hr
of red (18.1 ng/ml) or 8 hr of blue (17.0 ng/ml) light. Peak concen-
trations of GH in sera after TRH tended to be greater (p== 0.05) after
the first 5 wk of exposure to 8L116D (31.6 ng/ml. wk 5) or 5 wk of
exposure to 16L18D (38.h ng/ml, wk 10) than after the second 5 wk of
8 exposure to 8L116D photoperiods (21.1 ng/hl, wk 15). Lengths of daily
light did not affect (p> 0.10) 6H increase to TRH as measured by area
under the curve (Table 21). Time to maximum concentrations of GH after
injections of TRH averaged 10.5. 9.5 and 10.5 :1: 0.8 min (p> 0.10) when
light exposures were 8 (wk 5). 16 (wk 10) and 8 (wk 15) hr (Table 21).
In samples collected after injection of TRH during wk 5, 10 and 15,
disappearance of CH averaged 19.7. 21.6 and 1111.6 :1: 14.2 min (p> 0.10).
Differences between groups of bulls exposed to 16L18D photoperiods

composed of 8hr of ”cool white” light plus 8 additional hr of "red” or

"'blue" lights were not significant (p> 0.10) for any measurements of
I CH response to TRH with the exception of time to peak CH concentrations
after TRH injection, which was 7.0 min in bulls exposed to red light
and 12.0 min in bulls exposed to blue light. However, time to peak GK
concentration after*TRH was consistently short in this group of bulls.
averaging 8.0 and 6.5 min in wk 5 and 15, respectively.
0. Other Hormones

8 Concentrations of glucocorticoids decreased (p'< 0.05) from 2.6

to 1.# ng/ml when phot0periods were increased from 8L116D to l6L18D but

95

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96

returned to concentrations of 2.“ ng/ml when photoperiods were returned
to 8L116D. Concentrations of glucocorticoid did not differ (p> 0.10)
between groups of bulls exposed to 8 hr of ”cool white" light plus 8 hr
of red (1.? ng/nl) or 8 hr of blue (1.1 ng/hl) (Table 22).

Concentrations of Th increased (p«< 0.05) from 57.6 to 67.“ ng/ml
between wk 5 and 10 when photoperiods were increased from 8L116D to
16L18D. However, after 5 wk of 16L18D, when photoperiods were decreased
to 8L116D, serum.Tu continued to increase (p‘< 0.05) to 86.2 ng/ml by
wk 15. Concentrations of Ta in sera averaged 63.9 and 70.9 1:5.3 ne/ml
(p:> 0.10) in bulls exposed to 8 hr of "cool white” light plus 8 hr of
red or 8 hr of blue light (Table 22).

Concentrations of LH in serum from samples collected at 10 min
intervals during the first 7 hr of light on the last day of wk 5, 10
and 15 averaged 1.6, 2.11 and 2.0 :1; 0.3 ng/nl (p> 0.10. Table 23).
Average concentrations of LH in sera from bulls exposed to 8 hr of
white light plus 8 hr of red light were 2.7 :1; 0.11 ng/nl and did not
differ (p> 0.10) from LH concentrations in bulls exposed to 8 hr of
white light plus 8 hr of blue light (2.1 x 0.11 ng/ml). Similarly, when
daily light exposure was 8 hr during wk 5 and 15, the groups of bulls
did not differ in average LH concentration.

Although average concentrations of LH did not differ with time on
experiment or length of daily light. LH changes were not the same in all
weeks (p‘< 0.05). In five bulls (Figure 1h) the number of episodic
releases was less on the last day of wk 5 and 15 when photoperiods were
8L116D than on the last day of wk 10 when light exposure was 16L18D.

However, in two bulls (Figure 15) episodic releases of LH increased with

97

Table 22. --Glucocorticoid and thyrox ine (T11 ) concentrations in serum
after 5 wk of daily exposure of!+ bulls to 8.16 or 8 hr of
various wavelengths of light.

 

 

 

 

 

145111; Hormone (ng/ml)

(hr) (nil) Heek Clucocorticoida T45
8 300 - 750 5 2.6 57.6b
16 550 - 750° 10 1.7 63.9be
16 300 - 1125f 10 1.1 7o.9°
8 300 - 750 15 2.11 86.2ed
Mean 2.1 70.“
SE 0.3 5.3

 

a'lleans for wk 10 less than (p < 0.05) means for wk 5, 15.

bee-d1! means with different superscripts are significantly

6. ferent (p< 0.05).
98 hr of 300 to 750 on plus 8 hr of 550 to 750 1111 (red).
f8 hr of 300 to 750 nM plus 8 hr of 300 to 1125 um (blue).

98

Table 23.-Luteinizing hormone (LH) concentrations in serum
collected through cannulas at 10 min intervals for
7 hr after 5 wk of daily exposure of bulls to 8,
16 or 8 hr of various wavelengths of light.

 

 

 

 

Light

(hr) “(nn) ‘ week 18 (ngznl)°

16 550 - 750‘1 10 2.7 1.0.4

16 300 - uz5b 10 2.1 1.0.u
8 300 - 750 15 2.0 1.0.h

 

38 hr of 300 to 750 nn plus 8 hr of 550 to 750 nn (red).
b8 hr of 300 to 750 en plus 8 hr of 300 to u25 nn (blue).
cMean LH (mg/ml) does not differ (p> 0.10) after 5 wk of

8 or 16 hr of light daily, nor after exposure to red or blue
light.

99

Figure 14.--Luteinizing hormone (LH) concentrations in serum
collected from bull 596 on the last day after 5 wk
of daily exposure to 8. 16 or 8 hr of light.

LUTEINIZING HORMONE (ng/ml SERUM)

100

  

 

 

8L BULL 596
week 5

6 ..

4 .-

2 .—

0 l 1 1 1 W0

1100 1200 1300 1400 1500 1600 1700
3 BULL 596
week IO

   
     

 

I l l l l l L I 1 l . . ‘ 'l l 1
I200 I400 I600 le 2000 2200 2400

8' BULL 596
week l5

 

 

 

l l 1 4P 1 l i
IIOO I200 I300 I400 l500 I600 I700
H O U R S

101

Figure l5.--Luteinizing hormone (LH) concentrations in serum
collected from bull 599 on the last day after 5 wk
-of daily exposure to 8, 16 or 8 hr of light.

_ LUTEINIZING HORMONE (ng/ml SERUM)

 

102

F ' BULL 599
" week 5

 

 

 

 

 

I IOO I200 I300 I400 I500 l600 I700

I' BULL 599
~ week l0

 

 

I200 I400 I600 I800 2000 2200 2400

F BULL 599
* week l5

1.

t.

_L

l l L L L
I I00 . I200 I300 I400 I500 I600 I700
H 0 U R S

103

age of the bulls rather than with increased length of phot0period,
while in one bull episodic releases of LH decreased with increase in
age.
D. Feed Intake and Body Growth

Feed intake per 2'1 hr increased from 10 to 23 kg and from 9 to
25 kg in the two groups of bulls. In one group of four bulls, feed
intake increased 0.46, 0.32 (8 hr ”cool white" plus 8 hr ”red" light
daily) and 0.03 kg per 3. 5 days during the three 5 wk intervals
(p> 0.10. Table 211). In the second group. feed intake increased 0.115,
0.38 (8 hr ”cool white" plus 8 hr ”blue” light daily) and 0.83 kg per
3.5 days (p> 0.10). Rates of increase in feed intake did not differ
between the two groups of bulls during any of the 5 wk intervals
(p < 0.10). 0

Average heartgirths increased from 90 to 119 cm and from 86 to
117 cm in the two groups of bulls. Rates of change in heartgirth did
not differ between the two groups of bulls during either 8L116D or
16L18D photoperiods (p> 0.10; Table 211) nor did rate of change in
heartgirth differ within each group of bulls during exposure to 8 or
16 hr of light daily.

104

Table 24.--Increase in 24 hr feed consumption and heartgirth
measured twice-weekly during 5 wk of daily exposure
of two groups of bulls to 8, 16 or 8 hr of various
wavelengths of light.

 

 

 

 

 

Light Increase per 3. 5 days
(hr) (nH)__ weeks Feed intake (kg)f Heartgirth (cm)°
* 8 300-750 1- 5 0.116 1 0.31 0.68 :1: 0.23
16 550-7503 6-10 0.32 1.0.2u 0.98 1 0.31
8- 300-750 11-15 0.03 1.0.26 1.23 1.0.32
8 300-750 1- 5 0.45 1 0.211 0.78 1 0.36
16 - 300-1125b 6-10 0.38 1 0.111 0.83 1 0.114

 

‘8 hr of 300-750 nu plus 8 hr of 550-750 nn (red: four bulls per
treatment). .

b8 hr of 300-750 nh plus 8 hr of 300-u25 nn (blue; four bulls per
treatment).

cAverage increase (1 SE) during 5 wk exposure to 16 hr of light
composed of 8 hr of 300-750 nil cool white light supplemented with
8 hr of red or blue light not different (p> 0.10) from average
increases during 5 wk exposure to 8 hr of 300-750 nH light (wk 5
or wk 15); average increase (1 SE) during wk 5 not different from
wk 15 (p> 0.10) within each group of bulls studied.

DISCUSSION

The data presented confirm earlier reports that the length of
daily exposure to light is a major constituent of seasonal variation
in concentrations of Prl in sera from sheep (Pelletier. 1973; Forbes
et al., 1975) and cattle (Bourne and Tucker. 1975: Peters and‘Tucker,
1978). Furthermore. these results extend the effects of duration of
light to include effects of intensity and wavelength of light on con-
centrations of Prl. CH and other hormones in the bull calf.

Concentrations of Prl in serum from cattle changed within minutes
or hours after changes in ambient temperature (Hettemann and Tucker.
197k: Tucker and Hettemann, 1976). feed intake (Johke. 1970; McAtee
and Trenkle, 1971) or injections of drugs such as TRH (Scheme, 1972:
Convey et al., 1973; Kelly et al., 1973: Davis et al., 1977) or PCFai
(Louis et al., 19711). In contrast. gradual changes which mimicked
seasonal variation in concentrations of Prl paralleled, but occurred
several days after gradual changes in length of exposure to light
(Pelletier, 1973: Bourne and Tucker. 1975). In the present study
significant and sustained increases in concentrations of Prl in bulls
began within 1 wk after photoperiods were increased abruptly from
81.161) to 161.181) or 2011111). Bourne (unpublished) determined that con-
centrations of Prl increased as light exposure increased from 8 to 2h
hr, but continued exposure to constant illumination depressed Prl ,

approximately 5055 Collectively. data from my study and that of Bourne's

105

106

suggest that light exposures of 16 to 20 hr per 24 hr maintain maximal
concentrations of Prl in serum of bull calves.

In my study, increases in length of daily light exposure were
confounded with increased age of the bulls. The possibility was con-
sidered that increased age of the bulls would influence interpretation
ofresults because concentrations of Prl in the pituitary (Sinha and
Tucker. 1969) and serum (Davis et al., 1977) of holstein heifers
' increased between birth and 3 months of age. However, in prepubertal
bulls (Bourne and Tucker, 1975) and in rams (Pelletier. 1973; Ravault,
1976) Prl concentrations increased when phot0periods were increased to
16 hr of light and decreased when photoperiods decreased to 8 hr of
light regardless of increases in age. Therefore. it is probable that
increasing age did not influence significantly concentrations of Prl
after bulls were changed from 8L116D to 16L18D or 20LwhD photoperiods.
In addition, since the number of heifers was small and seasonal factors
were not considered, it is.equally likely that seasonal influences of
light and temperature may have produced the increases in pituitary and
serum.Prl between birth and 3 mo of age in the studies of Sinha and
Tucker (1969) and Davis et al. (1970).

In dairy cattle, repeated jugular venipuncture caused doubling
of basal concentrations of Prl in half of the cows tested (Tucker,
1971). Raud et a1. (1971) reported that concentrations of Prl in
samples collected from cattle by venipuncture were increased greatly
and more variable (100 to 200 ng/nl) than in samples collected through
cannulas (30 to 65 ng/hl). Concentrations of Prl did not differ

between samples collected by venipuncture or through cannulas when

10?

photoperiods were 8Ltl6D; however. concentrations of Prl in samples
collected through cannulas were 30 and 60% lower than values from
samples collected by venipuncture after 3 and 6 wk of exposure to 16
or 20 hr of light per day. It is not evident which method of blood
collection yields data which reflect true endogenous concentrations of
Prl. For example. Freeman believes that at least in rats. "stress”
was associated with chronic aortic cannulation. because two surges of
Prl were detected per 24 hr in sera collected from pseudopregnant rats
which were decapitated (Freeman et al., 197“). while only one surge
was found in pseudopregnant rats implanted with aortic cannulas
(Free-an and Neill. 1972). h

After injections of TRH in cattle. Prl was released (Convey et
al., 1973) in quantities which were related to the dose of m injected
(Vines et al., 1976). The amount of Prl released to a standard dose
of TRH varied with environmental temperature (Hettemann and Tucker.
197a. Tucker and Hettenann. 1976). length of daily light exposure
(Bourne. unpublished), and stage of lactation (Vines et al., 1977).
(Since repeatability among measurements of Prl (area under the hormone
response curve) released after*TRH was 0.61 while repeatability of
basal Prl concentrations in sanples collected through cannulas before
injection of run was only 0.27. Vines et al. (1976) suggested that
Prl response curve areas following administration of TRH were a more
acceptable measure of the capacity of the anterior pituitary to release
Prl than basal concentrations. They did note. however, that on any
individual day the correlation coefficient between basal and maximal

serum prolactin concentrations after'TRH was 0.6“. When photoperiods

108

were increased from 8le6D to 16L38D or to ZOLthD in my studies. peak
release of Prl after injection of TRH and area.of the Prl response
curve after injection of TRH increased 3— and 8-fold after 3 and 6 wk
of exposure. respectively. In contrast. average time to peak release
of Prl after injection of m was not modified 3 and 6 wk after daily
light exposure had increased from 8 to 16 or 20 hr per day. Average
time to peak Prl concentrations ranged between 6.7 and 7.3 min and were
similar to values previously reported (Vines et al., 1976).

In summary. basal concentrations of Prl in serum of prepubertal
bulls gradually increased with time after photoperiods were lengthened
'fron 8le6D'to 16L88D or ZOLth. regardless of whether estimates were
from sasples collected by venipuncture or through cannulas. Sinilar
increases in Prl released after injections of TRH also occurred when
photoperiods were lengthened. although the magnitude of increases was
greater than for basal Prl. Thus. it appears that increases in length
of daily light from 8 to 16 or 20 hr increased the capacity of the
anterior pituitary to release Prl.

Concentration of Prl in serum is a function of clearance rate
from the blood as well as secretion rate from the pituitary. Therefore.
it is not sufficient to assume that increase in number of hours of
daily light increased concentrations of Prl in serum solely via
increased pituitary secretion. For example. clearance rates of Prl
(unadjusted for body weight) were less in young than in mature sheep
(Davis and Borger. 1973) and cattle (Alters. unpublished). were related
inversely to temperature in steers (Smith et al., 1977). but were not

related to stage of the estrous cycle in ewes (Akbar et al., 197“).

109

However. length of photoperiod did not affect average clearance rate
of Prl in my study.

. In cattle. estimates of average disappearance rate (T%) of Prl
from serum ranged between 22 and #2 min (Tucker. 1971; Smith et al.,
19773 Akers. unpublished). In my study. average disappearance rate
(Ti) of Prl after infusion of exogenous Prl was discontinued ranged
between 31 and 327 min and were extremely variable. Perhaps variation
in releases of endogenous Prl accounted for the variability in dis-
appearance times after infusion of Prl. because estimates of average
disappearance time of Prl after injection of TRH ranged between 3“ and
41 min in accord with published values.

Reports on the influence of light intensity on Prl and on the
relationship between effects of intensity and hours of daily exposure
to light on serum Prl in cattle are not available. In my study. basal
concentrations of Prl collected by venipuncture or through cannulas
and TRH-induced releases of Prl in bulls exposed to 16L08D photoperiods
of 22 or 5h0.lux did not differ during the first 6 wk of exposure. but
were approximately doubled in bulls exposed to 5&0 lux during the sec-
ond 6 wk of the study. This increase between the groups of bulls was
the result of an increase in Prl in bulls initially exposed to 22 lux
for 6 wk prior to exposure of 5#O lux. whereas serum concentration of
Prl in bulls initially exposed to 540 lux for 6 wk remained unchanged
during subsequent exposure to 22 lux. In this study. average time to
peak release of Prl after'TRH (5.“ min) was not affected by light inten-
sity. and values were similar to those reported in my first experiment.

When light intensities were 22 and 5&0 lux. average disappearance times

110

of Prl after injection of TRH were 62 and 103 min. respectively
(P) 0.10). These estimates are greater than published values and may
reflect endogenous release of Prl from stimuli which are unrelated to
TRB or light intensities.

Concentrations of Prl in bulls exposed to 22 or 5&0 lux of light
did not differ during the first 6 wk of this study. Perhaps the bulls
had not adapted completely to the chambers during this time. However.
since estimates of basal and TRH-enhanced concentrations of Prl during
wk 12 were greater in bulls exposed to 500 than to 22 lux. I propose
that the capacity of the anterior pituitary to release Prl is greater
with increased intensities of light. Peters and Tucker (1978) report
evidence which supports the hypothesis that light intensity affects
changes in concentrations of Prl in cattle. Between April 30 and
August 15. concentrations of Prl in sera collected from 15 heifers
exposed to 16L38D photoperiods (average median light intensity of 29“
lux) averaged 78 ng/ml. while in 15 heifers exposed to natural day-
lengths (lb.7 hr average daily exposure with average median light
intensity of no lux) Prl averaged #8 ng/ml. It seems unlikely that a
1.6-fold difference in concentration of Prl could arise entirely from
1.3 hr’difference in length of light. since a difference of h hr of
light between groups of bulls exposed to 16L38D or 20LrbD photoperiods
in my first experiment did not result in significant differences in
concentrations of Prl. Certainly additional research on the effects
of light intensity on concentrations of Prl is warranted.

Publications on the effects of wavelengths of light on concentra—

tions of Prl in sera of cattle are not available. In my study. basal

111

concentrations of Prl collected by venipuncture or through cannulas
and TRH-induced releases of Prl were 2 to 5 times greater when bulls
were exposed to 16L18D photoperiods (8 hr of "cool white” light
supplemented with 8 hr of ”red” orwith 8 hrof ”blue" light) than when
bulls were exposed to 8L316D photoperiods. Thus. wavelengths of light
between 300 and 750 nM were equally effective in altering Prl concen-
trations. In fact. after 5 wk of daily exposure to 16 hr of light of
various wavelengths. concentrations of Prl were of the same magnitude
as concentrations in Experiments 1 and 2 when 16L38D photoperiods were
composed entirely of ”cool white” light.

In this study neither time to maximal concentration nor dis-
appearance rates (Ti) of Prl after injections of TRH were affected by
wavelength of supplemental light. Time to maximal concentration of Prl
and disappearance rates (Ti) of Prl after injection of TRH were similar
to times observed in my other studies and by other researchers. There-
fore. the increased capacity of the anterior pituitary to release Prl
as daily exposure to light was increased from 8 to 16 hr was not altered
by wavelengths of light between 300 and 750 nH.

In mature dairy cattle which were cannulated and allowed free
access to feed and water (Koprowski et al., 1972). concentrations of
Prl in sera collected hourly for 25 hr changed in an episodic pattern
with greatest values between 1000 and 1600 hr. In my study of wave-
length of light. average concentrations of Prl. in samples collected
through cannulas at 30-min intervals during the first 7 hr of light.
fwere greater’during exposure to the 16L38D photOperiod on wk 10 than

during 8le6D photOperiods on wk.5 or 15. However. within each 7 hr

112

concentrations of Prl were remarkably constant from one sampling point
to the next. irrespective of total hours of daily light exposure. Dif-
ferences between my study and that of Koprowski et a1. (1972) could
havebeen due to feed intake. diurnal variation in ambient temperatures
or differences in maturity of the cattle. In my study. calves were
watered but not fed. to avoid increases in basal concentrations of Prl
which have been observed after intake of feed (Johke. 1970: McAtee and
Trenkle. 1971). In my experiment ambient temperatures were constant
(20;: 2 C). whereas they were uncontrolled in the study of Koprowski

et a1. (1972). I suspect that gradual daily rise in Prl to a peak at
1600 'hrnoted by Koprowski et a1. (1972) could have been due to the
normal rise in ambient temperature. Furthermore. within my study. age
did not affect estimates of Prl from samples collected through cannulas.
because estimates at the end of wk 5 when animals were 1.? mo old were
not significantly different from concentrations at the end of wk 15
when animals were 3.3 mo old.

Chronic changes in CH concentrations in cattle have been associ-.
ated with energy content of the diet (Hove and Blom, 19733 Trenkle. _
1971) and genetic factors related to energy utilisation (Hart et al.,
1975). In addition. brief increases in concentrations of CH occurred
within minutes after injections of drugs such as TRH (Convey et al.,
1973) or PGFZa (Louis et al., l97fi). However. season of the year
I (Koprowski and Tucker. 1973: Head et al., 1976). length of daily light
(Bourne and.Tucker. 1975: Driver et al., 1976) and various temperatures
between “.5 and 32 C (Tumker and Hettemann. 1976) had no significant

effects on concentrations of GH in serum of cattle. Since average

113

concentrations of CH in sera from cattle exposed to 16L38D photo-
periods were not different from concentrations of CH observed in cattle
exposed to natural photoperiods (9 to 12 hr) during winter months
(Peters and Tucker. 1978). it did not seem likely that an affected
increased growth and lactation in cattle exposed to 16L38D photo-
periods (Peters et al., 1978).

My studies agree with previous studies because average concen-
trations of CH in sera of prepubertal bulls were not different during
6 wk of exposure to 8L316D. 16L38D or 20stD photoperiods. Similarly.
average concentrations of CH in sera of prepubertal bulls were not
different during 6 wk of exposure to 22 or 5h0 lux of light or during
5 wk of exposure to l6Ls8D photoperiods composed of 8 hr of ”cool white".
light supplemented with 8 hr of ”red” or 8 hr of "blue” light. In
contrast. variability of concentrations of CH was consistently less in
samples collected when bulls were exposed to 8le6D photoperiods or to
22 lum of light than when photoperiods were 16L38D (or 20LihD) or when
light intensity was 5&0 lux. Increased variation of CH concentrations
were probably not related to "stress" of blood collection. because
Tucker (1971) reported that rapid and repeated jugular venipuncture did
not affect GH concentrations in cattle. Furthermore. in my studies.
estimates of CH concentrations in samples collected by venipuncture
were not significantly different from concentrations in samples
collected through cannulas. In another study. variance in CH concen-
trations in cattle was less during intracarotid infusion of somato-
statin than during infusion of saline. although average CH concentra-

tions were not different (Hafs et al., 1977). Thus. it is possible

114

that length and intensity of light also my affect CH variability with-
out changing average concentrations of the hormone.

A decrease in variability of CH concentrations could be important
if the underlying cause of variability in samples collected twice-
weekly by venipuncture is an episodic release pattern of the hormone.
such as in rats (Tannenbaum et al., 1976). In that species. CH is
released in episodes. and the magnitude and frequency of CH releases
can be altered by changes in the diet. However. concentrations of CH
in samples collected through cannulas from mature dairy cattle were not
highly variable: concentrations of CH rarely exceeded 5 ng/al .
(Keprowski et al., 1972). In contrast. in my studies. concentrations
of CH in samples collected at 30 min intervals for 7 hr on the last day
of wk 5 (81.:16D photoperiods) and 10 (lanes photoperiod) exhibited a-
to 6-fold changes between nadir and peak concentrations. However. on
the last day of wk 15 (8le6D photoperiods) individual on values seldom
exceeded 10 ng/el. and changes in CH were not large. I am not certain
if decreased variation was related to effects of increased age of bulls
or to effects of 8le6D photoperiods which follow 5 wk of exposure to
16LI8D photoperiods. Collectively. information on variability of con-
centrations of CH in samples collected by venipuncture or through
cannulas suggests that length and intensity of light alter frequency
- and magnitude of releases of CH in prepubertal bulls.

Often injections of’TRH are used to test the capacity of the
anterior pituitary to release CH in cattle during different physio-
logical states. This is because releases of CH which were proportional
Ito dose of TRH have been reported in lactating cattle (Convey et al.,

1973) and prepubertal heifers (Vines et al., 1976). Furthermore.

115

baseline concentrations of CH prior to TRH were highly correlated
(0.60) with the magnituie of release of CH after injections of m
(Vines et al., 1976). As observed with basal concentrations of CH in
my studies. length. intensity and wavelength of daily light did not
affect maximal release of CH or area under the CH response curve
following injections of TRH. although values from bulls exposed to
8L3160 photoperiods tended to be less than values observed when photo-
periods were l6Ls8D. In my studies. time to peak release of CH after
TRH was not affected by length. intensity or wavelength of daily light
exposure. and average values were within the range of 5 to 12 min
reported previously (Vines et al., 1976). Disappearance rates (Ti)
of CH after injections of CH also agreed with previously reported
values of 22 to 50 min (Yousef et al., 1969; Bourne et al.. 1977).

Until effects of age and photoperiod on episodic release of CH
in cattle are defined further. it is impossible to evaluate completely
the effects of light on this hormone.

Maximal glucocorticoid concentrations were associated with feed-
ing in sheep (Holley et al., 1975). In rats. the time of day that food
was available determined the time of maximal concentrations of gluco-
corticoids (Krieger. 1973; Nelson et al., 1975; Takahashi et al., 1977;
Philippens et al., 1977). Information on environmental factors which
affect glucocorticoid.variability is limited for cattle. Since time
that cattle spent feeding increased in summer in comparison with winter
(Stricklin et al., 1976). it is possible that seasonal changes in feed-
ing behavior may modify glucocorticoid concentrations in cattle as well

as rats.

116

In my studies. intensity and wavelength of light did not affect
glucocorticoid concentrations in sera from bulls bled twice weekly by
venipuncture. However. concentrations steadily decreased after photo-
periods were increased from 8Ltl6D to 16L38D or 20Lth. Similarly.
glucocorticoid concentrations averaged 1.5 ng/el when photoperiods
were 16L38D and 2.6 ng/ml when photOperiods were 8Ltl6D. These differ-
ences could occur if overall concentrations of the hormone decreased
with increased hours of daily light exposure. or if shifts occur in the
daily release pattern of glucocorticoid secretion. Changes in patterns
of daily release of glucocorticoids without changes in overall concen-
trations have been observed if rats conditioned to normal light-dark
cycles are subsequently enucleated, eXposed to constant light orldark.
or eXposed to changes in feeding schedules(Krieger. 1973: Krieger
et al., 1977; Takahashi et al., 1977).

Concentrations of plasma and adrenal cortisol and adrenal corti-
costerone. as well as concentrations of CH in serum of heifers fed HGA
were significantly less than in untreated control heifers. yet HGA-
treated heifers grew 10:: faster than controls (Purchas et al., 1971).
Although small doses of glucocorticoid enhanced milk production in
early lactation (Swanson and Lind. 1976). pharmacologic doses of glu-
cocorticoids or ACTH depressed milk yields (Brush. 1960: Hartmann and
Kronfeld. 1973; Campbell et al., 196+). Thus. decreased glucocorticoids
have been associated with increased growth and lactation. whether the
increased growth and lactation observed by Peters et a1. (1978) in
response to 16L88D ph0t0periods is related to a decreased secretion of

adrenal glucocorticoids must await additional research.

117

A relationship between secretion of thyroid and anterior pitui-
tary hormones has been proposed because release of Prl and CH accompany
release of TSH at various intervals after injection of TRH in sheep
(Davis et al., 1976) and prepubertal heifers (Davis et al., 1977.
Keener et al., 1977). Also. in thyroidectomised sheep. Prl and TSH
were increased. presumably by decrease in tonic inhibition of m
(Davis and Borger. 1973). Conversely. basal and TRH-enhanced concen-
trations of Prl were decreased in sheep treated with tri-iodothyronine
(Debeljuk et al., 1973). However. chronic treatment of prepubertal
heifers with thyroprotein decreased concentrations of Ta without alter-
ing concentrations of Prl (Keener et al., 1977). Since change in thy-
roid hormone availability altered basal concentrations of serum CH and
Prl in sheep and rats (Peake et al.. 1973; Davisand Berger. 1973:
Eisenberg et al., 1972: Nicoll and Heites. 1963) it is possible that
light affects Prl and CH concentrations via changes in thyroid status.

Results from my studies do not support this hypothesis. Increase
in length of photoperiod from 81.:16D to 161.38!) or 20Lil+D did not change
concentrations of TSH in samples collected twicedweekly by'venipuncture.
Although TRH increased TSH. and greatest concentrations occurred by
9.? min after injection. length of photoperiod did not affect concen-
trations of TSH in samples collected through cannulas prior to or for
30 min after’TRH injections.

In my studies. Tu concentrations after 6 wk of exposure to
8L116D photoperiods were significantly less than after 3. but not 6.
wk of exposure to 16 or 20 hr of light per'day. Light intensities of
22 or 5&0 lux did not differ in effect on.Tu concentrations. Irrespec-

tive of wavelength or number of hours of daily light exposure. concen-

118

trations of T4 increased as bulls aged.

In summary. increase in length of light exposure from 8 to 16 or
20 hr daily did not influence concentrations of TSH or'Tu. and light
intensity and wavelength did not change concentrations of Tu in serum
of prepubertal bulls.

In other studies. factors which increased concentrations of Prl
in serum. such as season of the year or milking stimulus. did not
affect insulin concentrations in lactating cattle (Koprowski and Tucker.
1973. Head et al.. 1976). although insulin increased with advancing
~lactation (Koprowski and Tucker. 1973). Insulin concentrations in
cattle also varied with feed intake (Hove and Blon. 1973). In addition.
bull calves injected with.TRH within 30 min of their daily meal had
greater insulin concentrations and 10% greater growth rates than the
saline-injected control (HcCuffey et al.. 1977). In my study. neither
8le6D. 16L38D nor 20LiflD photoperiods affected concentrations of
insulin in samples collected by venipuncture from bull calves fed ad
libitum.

Photoperiods which were increased from 81.1160 or decreased from 16L38D
to 8L316D did not affect average concentrations of LH in serum collected from
prepubertal bulls at weekly intervals (Bourne and Tucker. 1975). However.
the frequency of blood sampling may not have been optimal for character-
ization of the influence of light on LH concentrations. because Haynes
et al. (1976) reported that concentrations of LH in serum of pubertal
bulls were released in an episodic pattern. Number of episodes of LH
ranged between 0 and 3 per 8 hr in serum collected from h-mo old bulls

(Haynes et al.. 1977). Although photoperiods affect In episodes in

119

rams from breeds of sheep which are seasonal breeders (Pelletier.
'1975a; Lincoln. 1976). changes in DH episodes would not be expected in
bulls because effects of season on fertility are not clearly evident.

In my study. in which bulls were bled through cannulas at BO-nin
intervals. concentrations of LH varied in an episodic pattern. In five
of eight bulls. the number of episodic releases of LH increased when
photoperiods increased from 8L316D to 16Lt8D and decreased when photo-
periods returned to 8L116D. However. changes in episodic release
patterns in the other bulls were not clearly defined and/or tended to
increase or decrease with increase in age of the bulls. Therefore. it
is not clear if LH episodes are related to age of the bulls. photo-
period exposure or a combination of both. Additional research in this
area is warranted. especially if changes of LH episodes are related to
onset of puberty in cattle and if 16L38D photOperiods can be used to
alter LH episodes and hasten puberty.

Peters et al. (1978) observed that Holstein heifers exposed to‘
16 hr of fluorescent lighting daily between Noveaber and March grew 105
,faster than heifers exposed to seasonal changes in daily light exposure
(9 to 12 hr). However. in my studies. length. intensity and wave-
length of light did not affect changes in feed intake or growth
seasured by heartgirth. Since hormonal changes were not apparent until
3 wk after light exposures were changed. it seems likely that 5 to 6
wk of exposure to light treat-ants may not be long enough for effects
on feed consuaption or growth.

SPECULATIONS

I conclude from data presented in this thesis and from literature
reviewed that. in comparison with 8L316D photoperiods. 16L38D photo-
periods may be used to increase concentrations of Prl. increase vari-
ation in concentrations of GH and decrease concentrations of gluco-
corticoids in sera of cattle. Similarly. light intensities greater
than 22 lux may act additively with length of photoperiod to increase
concentrations of Prl and variation of concentrations of GH. However.
various wavelengths of light between 300 and 750 nM were equally
effective in altering Prl concentrations.

Indications are that Prl. GH and glucocorticoids are key hormones
in the control of growth and lactation in cattle. For example. injec-
tions of TRH. a hormone which increases Prl. GH. TSH and glucocorticoids
in sera of cattle (Schams. 1972; Convey et al.. 1973; Kelly et al..
1973; Vines et al.. 1976; Davis et al.. 1977), also enhanced growth 10%
in prepubertal bulls (McGuffey et al.. 1977) and heifers (Davis et al..
1977). Similarly. in mature cattle. Prl. GH and glucocorticoids were
enhanced during the periparturant period (Ingalls et al.. 1973; Smith
et al.. 1973). and TRH-induced increases in these hormones (Karg and
Schams. 1974) enhanced subsequent milk yields. Evidence suggests that
the prepartum surge in Prl may be most critical for milk production.
because if this surge is blocked with ergocryptine milk yields are
reduced markedly (Fell et al.. 197“; Karg and Schams. 197“). In con-

trast. once lactation is initiated. increased GH concentrations
120

121

(Donker and Peterson. 1951; Bullis et al.. 1965; hachlin. 1973; hart

et al.. 1975; Bourne et al.. 1977) and low glucocorticoid concentrations
(Brush. 1960; Hartmann and Kronfeld. 1973; Campbell et al.. 1961;) may
be optimal for maximal lactation. These conditions may be met with
16Ls8D.phctoperiods.

Recent research on the use of light as a management tool has
shown promise; exposure of Holstein cattle to 16bt8D photoperiods in-
creased body weight gains and milk yields 10 to 151 without proportion-
ate increases in feed intake in comparison with cattle exposed to
natural photOperiods in central Michigan between Nevember and March
(Peters et al.. 1978; Peters et al.. unpublished). Although increases
in concentrations of Prl associated with 16L38D photoperiods are more
dramatic than are changes in the other hormones. temperatures less than
0 C decrease the ability of 16 hr of light to increase Prl in winter
months (Peters and Tucker. 1978). Therefore. it is not likely that
increases in growth and lactation are due solely to increases in Prl;
rather. an and glucocorticoids probably are involved also. Thus. the
meshanism(s) whereby light affects growth and lactation are not clearly
defined. Nonetheless. use of hormone concentrations in sera to optim-
ise photoperiod (or other stimuli) may be a reasonable approach to
maximise the response of production traits in cattle.

To summarize. I conclude that light can be used to alter hormones
associated with body growth and lactation. and I speculate that light

may be used to enhance productivity of dairy cattle.

SUMMARY AND CONCLUSIONS

Holstein bulls. 5 to 18 wk of age and 52 to 150 kg body weight
at the beginning of the experiments. were used in studies designed to
evaluate effects of duration. intensity and wavelength of light on
concentrations of Prl. GH. glucocorticoids and other hormones in serum.
Bulls were housed in environmentally controlled chambers and fed a com-
lplete pelleted ration ad libitum. In all studies. blood was collected
- twice-weekly by venipuncture at the midpoint of the photoperiod. In
studies involving multiple sampling of blood. such as TRH challenges.
Prl infusions or studies of diurnal variation. blood was collected
through cannulas.

i In a study designed to evaluate the effects of an abrupt increase
from 8 hr to either 16 or 20 hr of 650 lur of light (300 to 750 nu:
"cool white" fluorescent) per day. Prl concentrations in samples col-
lected “ by venipuncture averaged 9.3 and 5.9 ng/ml serum (p> 0.10) in
two groups of bulls subjected to 8L316D photoperiods for 6 wk. Hithin
7 days after photoperiods were increased from 8L316D to either 16L¢8D
or ZOLth. Prl concentrations increased 113% (p;< 0.05). The log of
the Prl concentration continued to increase at 0.02 ng/ml per day to
averages of 66.8 or 55.8 ng/ml (p> 0.10) during the 3rd through 8th
wk of exposure to 16 or 20 hr of light daily.

Average concentrations of GH in samples collected by venipuncture

ranged between 8.3 and 11.7 ng/ml (p> 0.10). whereas variations of

122

123

concentrations of CH were less (p < 0.01) when photoperiods were
8L816D (s2 - 30.8) than when light exposure was 16 or 20 hr per day
(s2 - 21+2.2).

Concentrations of glucocorticoids in samples collected by veni-
puncture were 2.8 ng/ml after 6 wk of daily exposure to 8 hr of light.
decreased (pi< 0.05) to 1.8 ng/ml 3 wk after exposure to 16 or 20 hr
of light daily. and remained low (1.1+ ng/ml) after 6 wk of exposure to
16 or 20 hr of light daily.

In the 1st wk of this study. concentrations of TSH averaged
4.2 ng/mls thereafter concentrations steadily decreased (p«< 0.05) to
3.2 ng/ml during wk 12. Although concentrations of Ta increased
(p < 0.05) 1.2-fold from 56.1; to 67.3 ng/ml 3 wk after photoperiods
were increased from 8Lil6D to 16L38D or 20L38D. this increase was not
sustained through the 6th wk of exposure to 16 or 20 hr of light per
day. It is not likely that changes in Ten and Tu were caused by
increases in number of hours of daily light exposin‘e.

length of daily light did not affect concentrations of insulin
which ranged between 2.3 and 2.5 ng/ml (p> 0.10).

A second study was designed to explore the effects of daily
exposure to 16 hr of light at 22 or 5&0 lux (300 to 750 nH; ”cool
white” fluorescent) on hormone concentrations. Concentrations of Prl
in groups of bulls exposed to 22 and 51m lux of light did not differ
(p > 0.10) during the first 6 wk of the study. However. concentrations
of Prl (increased 1. 5-fold (p z 0.05) in sera from bulls which received
6 wk of 5&0 lux after initial exposure to 22 lux. whereas concentra—

tions of Prl in sera from bulls which received 6 wk of suo lux

121+

(154.8 ng/ml) followed by 6 wk of 22 lux (ul.8 ng/ml) did not change
(P > 0.10).

Although average concentrations of GH were nearly equal (10.6
and 13.6 ng/nl; p> 0.10) when light intensities were 22 and 51m lux.
variability was less (p < 0.01) at light intensities of 22 lux
(s2 - 791+) than at suo lux (s2 - 321.8).

In this study. concentrations of glucocorticoids averaged 1.2
and 1.8 ng/ml but did not differ (p> 0.10) in bulls exposed to 5&0 or
22 lux for 16 hr per day. Similarly. concentrations of Th did not
differ (p> 0.10) in bulls exposed to 16 hr of 22 (77.3 ns/Il) or 5‘00
(78.1; ng/nl) lux of light per day.

A third study was designed to evaluate the effects of ”red”
(550 to 750 nh) or "blue" (300 to 1.25 nh) light on hormones. Serum
Prl concentrations in samples collected by venipuncture decreased
(p < 0.05) from 19.6 to 10.1; ng/ml within 5 wk after bulls were taken
from natural environmental conditions (June) and exposed to 8Lil6D
(540 lux. "cool white” fluorescent) photoperiods. Subsequent exposure
to 16L38D photoperiods composed of 8 hr of ”cool white” light supple-
mented with 8 hr of ”red” or ”blue” light resulted in increases
(p < 0.05) of Prl to concentrations of 57.2 (red) and 37.5 (blue) ng/ml
(p > 0.10). when photoperiods were returned to 8L;16D for 5 additional
wk. serum Prl decreased (p < 0.05) to 26.14; and 6.2 ng/ml (p> 0.10) in
bulls which had been eXposed to ”red” or "blue" light. After 5 wk of
daily exposure to 16 hr of light of various wavelengths. concentrations
of Prl were of the same magnituie as concentrations when 16L38D photo-

periods were composed entirely of ”cool white” light.

125

Concentrations of CH averaged lo.u ng/ml during the first 5 wk
exposure to 8Lil6D photoperiods. Five weeks' exposure to an additional
8 hr of "red" or "blue" light did not affect (p:> 0.10) concentrations
of CH. which averaged 14.0 and 10.9 ng/ml. respectively. However.
during the last 5 wk of this study when light exposures were reduced
to 8 hr of ”cool white” light. concentrations of CH decreased (p;< 0.01)
to an average of 5.6 ng/ml.

Concentrations of glucocorticoids in samples collected by veni-
puncture were less (p;< 0.05) when photoperiod was 16L18D (1.“ ng/hl)
than when photoperiod was 8L;16D (2.6 ng/ml. wk 5; 2.1; ng/ml. wk 15).
In contrast. increased concentrations of T1; (from 57.6 to 86.2 ng/nl)
seemed to be related to age of the bulls rather than duration of daily
light exposure. wavelengths of light between 300 and 750 nH altered
concentrations of glucocorticoids or'Th with equal efficacy.

Samples also were collected at 30-min intervals for 7 hr on the
last days of wk 5. 10 and 15. Concentrations of Prl were greater
(p‘< 0.01) when photoperiods were 16L38D (17.0 ng/ml) than when photo-
periods were 8L;16D (1+.5 ng/ml. wk 5; 5. 5 ng/hl. wk 10). Concentrations
of GH were released in an episodic pattern which ranged between 5 and
50 ng/ml during wk 5 and 10. whereas episodes of CH were absent and
concentrations of CH seldom exceeded 10 ng/ml on wk 15.

Number of episodes of LH were greater in five of eight bulls
when photoperiods were 16L38D than when photoperiods were 8Lil6D. The
possibility that LH and CH episodes are related to age of the bulls or
to a combination of age and hours of daily light exposure cannot be

eliminated.

126

To estimate the effects of ”stress” of blood sampling methods
in these experiments. concentrations of Prl (-30 and 0 min samples)
and CH (-15 and 0 min samples) in sera collected through cannulas prior
to TRH challenges were compared with concentrations of the hormones in
two samples collected by venipuncture during the same week of the TRH
challenges. Concentrations of Prl in samples collected through can-
nulas were 0 to 605 less (p < 0.01) than. but concentrations of CH were
not different (p> 0.10) from concentrations in samples collected by
venipuncture. Although method of blood collection affected concentra-
tions of Prl. changes in Prl and CH in samples collected through
cannulas associated with effects of duration. intensity or wavelength
I of light were proportional to changes observed in samples collected by
venipuncture. In addition. measures of peak concentrations of Prl and
CH and area of the hormone response curve after injections of TRH
(33 (lg/100 kg BH) were prepartional to changes in samples collected
by venipuncture.

Duration. intensity and wavelength of light exposure did not
affect (p> 0.10) time required to reach maximal Prl and CH after TRH
(1+ to 7 min. I’rl; 10 to 14 min. CH). nor did they affect disappearance
rates (Ti) of these hormones (p> 0.103 3 to 7 min. Prl; 20 to 53 min.
CH). Length of daily light exposure did not alter (1)) 0.10) metabolic
clearance rates and disappearance time of endogenous Prl after infusion
of exogenous Prl. However. estimates were sometimes greater than
results previously published. which may reflect endogenous releases of
Prl caused by stimuli unrelated to amount of Prl infused. TRH injected

or quality of light exposure.

127

In these studies. various durations. intensities or wavelengths
of light exposure did not affect changes in feed intake (0.03 to 1.17
kg per 3.5 days: p:> 0.10) or rate of increase in heartgirth (0.68 to
1.31 on per bull per 3.5 days; p> 0.10). Perhaps 5 to 6 wk was not
long enough for light to affect feed consumption or growth in cattle.

I conclude that increases in length of daily light from 8 to 16
or 20 hr and increases in light intensities from 22 to 540 lux increased
the capacity of the anterior pituitary to release Prl. and may increase
episodic releases of CH and LH. However. age of the bulls also may
affect episodic releases of CH and LH. Daily light exposures of 16 hr
also decreased concentrations of glucocorticoids when compared with
8Lil6D photoperiods; however. wavelength and intensity of light expo-
sure did not affect concentrations of glucocorticoids. In addition.‘
effects of length. intensity and wavelength of light on TSH. Tu and
insulin were not obvious. The results from this series of experiments
provides substantial evidence that length and intensity but not wave-
length of daily light exposure may be used to alter hormones associated
with body growth and lactation in cattle.

APPENDIX

APPENDIX

Appendix 1. Diets

A different batch of Purina Bir Milking Chow was fed ad libitum in
each experiment. Composition of the diet (per label) was: grain prod-
ucts. plant protein products. processed grain by-products. roughage
products. forage products. cane molasses. urea. vitamin A supplement. D
activated animal sterol. defluorinated phosphate. calcium carbonate. salt.
iron oxide. vitamin E supplement. manganous oxide. magnesium oxide.-ca1-
cium iodate. copper oxide. cobalt carbonate. zinc oxide.

Forage analysis was conducted by the Ohio Livestock Ration Evalua-
tion Center. In the first experiment trace mineralized salt was not
available. in subsequent experiments the animals were allowed Crystal
Flow (Michigan Salt Co.. St. Louis. 141) trace mineralized salt ad libitum.
The guaranteed analysis of this salt (per label) was:

 

fligggal ZLComposition
Co 0.012
Mg 0.228
Cu 0.0h0
Fe 0.160
I 0.007
Zn 0.011
NaCl 96.0 (min). 98.0 (max)

128

129

Forage analysis for principle components of the three batches of

 

 

 

 

 

feed was:
06mposition ‘1_1
Component Experiment 1 Experiment 2 Ekperimentg3
P 0.48 0.50 0.33
K 0.97 1.28 1.2?
Ca 0.46 0.66 0.86
Mg 0.25 0.31 0.31
Na -- 0.17 0.11
Si -- 0.21 0.21
S 0.08 0.21 0.23
dry matter 87.50 86.19 91.01
crude protein 12.00 19.02 19.75

Forage analysis for trace minerals of the three batches of feed

 

 

 

 

was:
PPH Composition
Mineral Experiment 1 Experiment 2 Ekperiment;3
Mn 35 #2 45
Fe 220 243 213
Bo 12 15
Cu 12 15 13
Zn #7 55 an
A1 293 330
Sr 27 28
Ba 7 6

he I 0.68 1.60

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