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EFFECT OF PORCINE SOMATOTROPIN. SOYBEAN OIL AND
ENERGY INTAKE 0N MAMMARY DEVELOPMENT IN GESTATING GILTS

presented by

Kimberly Ann Howard

has been accepted towards fulfillment
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EFFECT OF PORCINE SOMATOTROPIN, SOYBEAN OIL AND ENERGY INTAKE ON MAMMARY
DEVELOPMENT IN GESTATING GILTS

BY

Kimberly Ann Howard

A DISSERTATION

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

DOCTOR OF PHILOSOPHY

Department of Animal Science

1995

 

ABSTRACT

EFFECT OF PORCINE SOMATOTROPIN, SOYBEAN OIL AND ENERGY INTAKE ON MAMMARY
DEVELOPMENT IN GESTATING GILTS

BY

Kimberly Ann Howard

Three studies were conducted to determine the influence of porcine
somatotropin, dietary soybean oil (880) and energy intake on gilt (n =
37, 27 and 34, respectively) mammary development during late gestation.
In each study, gilts were killed and total mastectomies were performed
on d 105 of gestation. Mammary tissue was separated into parenchymal
and extra—parenchymal tissue. Parenchymal tissue was weighed and
analyzed for DNA, RNA, water, protein and lipid. Treatments in the
first study were dietary energy (6.1 or 10.5 Mcal ME-d'll and porcine
somatotropin (0 or 8 mg-d'1 PST). In the second study treatments were
additions of 0 or 5% SEC to the diet. Treatments were initiated on d
75. Compared with placebo-injected controls, gilts injected with PST
had more (P < .05) parenchymal tissue (1609 9 vs 1963 9; SEM = 136.5).
Compared with placebo-injected controls fed adequate energy diets, PST-
injected gilts fed adequate energy diets had more (P < . 05) parenchymal
DNA, RNA and protein. Feeding elevated energy inhibited the positive
effect of PST on mammary secretory tissue growth. Parenchymal weight,
DNA, RNA and protein were not altered (P > .10) by feeding 5% $80 from d
75 to 105 of gestation. Treatments in the third study were energy
intakes of 6.1 or 10.5 Mcal ME-d‘1 fed over two periods (d 0 to 74 and d

75 to 105 of gestation), to achieve variation in body composition over

the last third of gestation. Body composition was measured on d 75 and
105 of gestation. Total parenchymal weight, parenchymal DNA,
parenchymal RNA and parenchymal protein were not altered by feeding
elevated energy diets regardless of the gestational period in which
elevated energy was fed. In addition, total DNA and RNA on d 105 were
not related (P > .10) to empty body fat or protein on d 75 or 105, or to
changes in empty body fat or protein from d 75 to 105. In conclusion,
elevated dietary energy and 5% SEC additions in late gestation did not
enhance or impair mammary development; however PST injections increased
mammary secretory tissue. Results of these studies strengthen the

potential for use of PST in commercial swine production to improve milk

production.

 

DEDICATION

This dedication is to my family because without their love, support and
guidance the completion of my dissertation would not have been possible.
My mother, Joyce, has inspired me throughout my life to achieve the best
that I am capable of. My brothers and sister-in-laws, Ricky, Bobby,
Corinne and Alice, supported me in the good times as well as the bad.
My father, Richard, had a determination to succeed which he shared with
my brothers and myself. My niece, Leilani, and nephews, Brandon,
Clinton and Nicholas, allow me to see through the eyes of a child and

marvel at the joy it is to be alive.

iv

ACKNOWLEDGIIITS

My Ph.D. program from the onset has been the cooperative effort of
many people in the Department of Animal Science, it would not have been
possible to complete the program without these people or the funding
provided from the department. I would especially like to thank Dr.
Thulin, Dr. Ullrey and Dr. Rozeboom for serving as my major advisors.
Dr. Thulin hired me initially and taught me practical aspects of swine
nutrition. Dr. Ullrey served as my interim advisor and introduced me to
the comparative nutrition world. Dr. Rozeboom, my final major advisor,
assisted with my last experiment and served as the primary reviewer for
my dissertation. My committee members Dr. Miller, Dr. Romsos, and Dr.
Tucker helped in all aspects of my program. The swine crew, Ray Kromer,
Steve Musell, Duwain Simon and Al Snedegar, assisted with my trials at
the swine research farm. I spent many mornings with Tom Forton and his
crew in the meat lab and appreciate all of their help. Sharon Debar and
Dr. Pao Ku provided laboratory assistance. Angelo Napolitano and Phil
Summer provided assistance at the mink farm. Many graduate students
provided friendship, support and assistance at the farm, in the lab or
in 204 Anthony Hall. A partial list of these people include Dan
Jennings, Scott Kramer, Michelle Mater, Daniel Nelson, Steve Radecki and
Josep Garcia-Sirera. Last but not least, Judy Bishop and Rita House
provided both technical assistance and friendship. Thanks to everyone

at MSU!

TABLE OF CONTENTS

LIST OF TABLES ..................................................... viii
LIST OF FIGURES ....................................................... x
LITERATURE REVIEW, Mammary Development in the Pig ..................... 1
Introduction ........................................................ 1
Anatomy ............................................................. 1
Endocrinology ....................................................... 3
Conceptus number .................................................. 3
Thyrotopin releasing hormone ...................................... 4
Growth hormone in the pregnant and lactating pig .................. 4
Growth hormone in other species ................................... 7
Nutrition and Mammary Development ................................... 9
Swine ............................................................. 9
Other species ..................................................... 9
Dietary fat ...................................................... 12
Body Composition .................................................. 14
Techniques ....................................................... 14
Body composition and mammary development ......................... 15
Conclusion ......................................................... 16

CHAPTER 1. EFFECTS OF EXOGENOUS PORCINE AND DIETARY ENERGY ON

MAMMARY DEVELOPMENT OF SWINE DURING LATE GESTATION ................... 17
Abstract ........................................................... 17
Introduction ....................................................... 18
Materials and Methods .............................................. 19
Results and Discussion ............................................. 21
Implications ....................................................... 25

CHAPTER 2. DIETARY SOYBEAN OIL DOES NOT INFLUENCE MAMMARY
DEVELOPMENT OF GILTS WHEN FED FROM DAY 75 TO DAY 105 OF GESTATION....32

Abstract ........................................................... 32
Introduction ....................................................... 33
Materials and Methods .............................................. 34
Results and Discussion ............................................. 35
Implications ....................................................... 37

CHAPTER 3. NUTRITION, BODY TISSUE ACCRETION AND MAMMARY DEVELOPMENT

IN PREGNANT GILTS .................................................... 41
Abstract ........................................................... 41
Introduction ....................................................... 42
Materials and Methods .............................................. 43
Results and Discussion ............................................. 46

vi

vfi

Implications ....................................................... 53

GENERAL DISCUSSION ................................................... 62

LITERATURE CITED ..................................................... 68

LIST OF TABLES

Table 1. Composition and calculated analyis of experimental diets ..... 27

Table 2. Effects of dietary energy and porcine somatotropin on sow
weight and carcass composition ........................................ 28

Table 3. Characteristics of mammary tissue from gilts at d 75 or
105 of gestation ...................................................... 29

Table 4. Effects of dietary energy and porcine somatotropin from
d 75 to 105 of gestation on mammary parenchymal tissue ................ 30

Table 5. Effects of dietary energy and porcine somatotropin from
d 75 to 105 of gestation on mammary extraparenchymal stromal tissue...31

Table 6. Composition and calculated analysis of experimental diets....38

Table 7. Effect of soybean oil on fetal and gilt mammary
characteristics ....................................................... 39

Table 8. Composition of mammary parenchymal tissue in gestating
gilts fed diets with soybean oil ...................................... 40

Table 9. Composition and calculated analysis of experimental diets....54

Table 10. Prediction equations developed to estimate body composition
in gravid and nongravid gilts ......................................... 55

Table 11. Body weights, backfat and empty body composition for gilts
fed adequate or elevated energy over two feeding periods (d 0 to 74
and d 75 to 105 of gestation) ......................................... 56

Table 12. Reproductive measurements for gilts fed adequate or
elevated energy over two feeding periods (d 0 to 74 and d 75 to 105
of gestation) ......................................................... 57

Table 13. Extraparenchymal and parenchymal tissue constituents of
gilts at various stages of gestation .................................. 58

Table 14. Regression analysis of parenchymal DNA and RNA on
parenchymal constituents and extraparenchymal percentage at d 105 of
gestation ............................................................. 59

Table 15. Extraparenchymal and parenchymal tissue constituents at
d 105 of gestation for gilts fed adequate or elevated energy over
two feeding periods (d 0 to 74 and d 75 to 105 of gestation) .......... 60

Table 16. Parenchymal tissue DNA and RNA at d 105 of gestation for
gilts fed adequate or elevated energy over two feeding periods
(d 0 to 74 and d 75 to 105 of gestation) .............................. 61

Table 17. Composition of mammary tissue in gestating gilts fed diets
with adequate or elevated energy levels ............................... 66

LIST OF FIGURES

Figure 1. Relationship of parenchymal DNA to gilt body weight ......... 67

LITERATURE REVIEW

Mallory Development in the Pig

IEEEQQHESLQB

The goal to increase sow productivity continues to be a high priority
in commercial swine production. To increase the number of pigs weaned
per sow per year and litter weaning weights, the sow must produce more
milk. The association between nutrition and the growth of milk
secretory tissue during gestation is not well understood, and must be in
order to maximize milk production in the sow. Deoxyribonucleic acid is
an indicator of mammary secretory cell number (Tucker, 1987), because
the DNA content per mammary cell nucleus is constant during pregnancy
and lactation (Tucker and Reece, 1962). Ribonucleic acid is a
reflection of the functional state of the cell, and the RNA/DNA ratio is
an indicator of protein synthesis activity per cell in the mammary
gland. Total DNA (r a .85) and RNA (r = .93) in the rat mammary gland
were highly correlated with total litter weight gains (Tucker, 1969).
Due to the relationships between mammary DNA, mammary cell number and
milk production, differences in mammary DNA can be used as an indicator

of subsequent milk production differences.

m

The anatomy of the swine mammary gland has been known for decades
(Turner, 1952). Swine mammary glands extend over the entire abdominal
wall in the form of two parallel gland areas with each gland being
separate and distinct from the other glands. Teat number usually ranges

between 10 and 14 with each teat connecting to a pair of glands. The
1

arterial circulation supplies the posterior glands from the aortal
branch, while the common carotid artery supplies the anterior glands.
Anastomosis occurs between the second and fourth inguinal glands for the
anterior and posterior mammary arteries and veins. Teats of swine
usually have two streak canals which open into two distinct teat
cisterns which lead into gland cisterns. Above the gland cisterns,
ducts branch to all parts of the gland tissue. The ducts lead to lobes
which contain lobules with alveoli (milk secretory cells).

Little change occurs in the amount of DNA in the swine mammary gland
prior to d 50 of gestation (Hacker and Hill, 1972). Hacker and Hill
(1972) studied mammary development in pigs at estrus, d 25, d 50 and d
100 of gestation. They found that approximately 100% of the increase in
parenchymal tissue weight, parenchymal DNA and parenchymal RNA was
accounted for in the last half of pregnancy. Kensinger et al. (1982)
found similar results in swine with mammary DNA concentrations
increasing four-fold between d 75 and d 90 of gestation. Amounts of
parenchymal tissue and parenchymal DNA plateaued at d 90 of gestation
while parenchymal RNA steadily increased through d 4 of lactation. The
increase in RNA represents increases in protein synthetic capabilities
of the mammary cell which is in agreement with Hacker and Hill (1972)
who found that RNA:DNA ratios also increased through pregnancy.

Histological results in swine show progressive duct growth early in
pregnancy followed by rapid lobulo-alveolar development between d 75 and
d 90 of gestation to complete mammogenesis (Kensinger et al., 1982).
Likewise, Weldon et al. (1991) demonstrated significant increases in
mammary growth in the pig between d 75 and 105 of gestation. These

results are further substantiated by Noblet et al. (1985) who

demonstrated that there was a 20% decrease in the amount of mammary
tissue fat from mid-pregnancy to late pregnancy in swine. As the day of
gestation and level of feed intake increased (d 75 to d 102; 1.8 kg/d to
2.5 kg/d, respectively), the weight of mammary tissue also increased
(902 g to 2885 g). Mammary tissue weight and chemical composition
increased exponentially with stage of gestation. In addition,
increasing feeding level increased mammary tissue weight at d 102 of
gestation. Thus, it seems that the majority of mammary secretory tissue

growth occurs during late pregnancy in the pig.

W

COnceptus number. Mammary development is stimulated by the presence
of conceptuses, most likely due to the concurrent rise in estrogen which
occurs with fetal growth. Dehoff et al. (1986) used psuedopregnancy to
investigate the influence of conceptus number on mammary development.
Psuedopregnancy was induced in non-gravid cycling gilts by injecting
estradiol valerate from day 11 to 15 of the estrous cycle.
Psuedopregnant gilts had 22% less mammary DNA than pregnant gilts by d
110 of gestation; however, mammary development did not differ when
conceptus number ranged between 4 and 13 (Dehoff et al., 1986; Noblet et
al., 1985). Dehoff et al. (1986) suggested that estrogen may be the
primary conceptus-derived mammogenic hormone in gilts due to significant
correlations between estrogen-sulfate or estrone concentrations in blood
and maternal mammary DNA content. The major rise in circulating
estrogens began between d 60 and 75 of gestation, which is associated

with the major period of mammary growth.

Thyrotropin releasing hormone. Mammary secretory tissue growth in the
pig may be related to changes in the concentrations of other hormones.
Grieshop et al. (1991) reported that injecting thyrotropin releasing
hormone (TRH) during a 28-d prepubertal period and a 50-d prepartum
period (d 64 of gestation to parturition) increased DNA concentrations
and 21-d piglet milk consumption. However, total DNA and the amount of
mammary parenchymal tissue did not differ. Feed consumption during the
lactation period increased as TRH levels increased which confounded the
effects of feed consumption and TRH levels on 21-d piglet milk
consumption. It is possible that the increase in milk production was
related to the increase in feed consumption during lactation which could
explain the lack of differences in total DNA and parenchymal tissue.
Feed intake may be one of several other factors influencing milk
production.

Growth hormone in the pregnant and lactating pig. Plasma
concentrations of growth hormone (GH) remain fairly constant throughout
pregnancy in swine (12 ng/ml), rising during the periparturient period
(Dehoff et al., 1986). Fetal GH concentrations increase from d 60 and
peak at d 90 ( > 150 ng/ml) of gestation, however maternal
concentrations of GH remain low, which indicates that GH may not cross
the fetoplacental barrier (DeHoff et al., 1986).

Sows injected with growth hormone during gestation and lactation had
higher IGF-I and glucose concentrations compared with non-injected
controls (Baile et al., 1989; Smith et al., 1991). Okere and Hacker
(1995) injected gestating gilts with 5 mg/d porcine somatotropin and .5
IU/kg insulin from d 30 to 70 of gestation and found that maternal serum

IGF—I levels and maternal d 133 BW were increased but there was no

difference in piglet serum IGF-I levels suggesting that IGF-I production
in maternal and fetal compartments are independent. Gregor and Burleigh
(1985) have demonstrated in sows that there are receptors for IGF-I on
mammary epithelial cells. Kvergas et al. (1986) found that pigs from
GH-injected sows during late gestation had higher total body lipids,
serum glucose concentrations, and liver glycogen concentrations at birth
and tended to have increased mean free fatty acid concentrations.

The influence of growth hormone on swine mammary DNA and RNA has not
been directly studied; however, there have been several studies
conducted involving injections in late gestation (Baile et al., 1989;
Boyd et al., 1984; Crenshaw et al., 1989; Cromwell et al., 1989b;
Kvergas et al., 1986) and through lactation (Cromwell et al., 1989a;
Harkins et al., 1989; Smith et al., 1991) to determine the influence of
growth hormone on sow lactational performance. The studies produced
conflicting results.

Although some reports show increased milk production for sows
injected with growth hormone during gestation, the majority of reports
indicate that milk production is not effected in sows injected as early
as d 91 of gestation. Sows injected with an isolated porcine growth
hormone preparation (USDA/NPA, 4.5 Iu-mg‘l, 24 IU-sow'l-d'l) from d 100
of gestation to d 21 of lactation produced 15% more milk by d 21 of
lactation; however, milk yields were similar at d 14 of lactation (Boyd
et al., 1984). Contradictory to this work, injecting sows with PST
beginning as early as d 94 of gestation, with or without 8% added fat,
did not increase milk yield or piglet body weight (Baile et al., 1989;

Crenshaw et al., 1989; Cromwell et al., 1989b; Kvergas et al., 1986).

Similar to PST-injection during late gestation, injection during
lactation has not resulted in consistent increases in milk production.
Harkins et al. (1989) found that injecting lactating sows daily with
porcine somatotropin (PST) from d 12 through d 29 of lactation increased
milk production 22% and increased piglet weights (.34 kg/pig) at the end
of the lactation period. However, milk composition was similar for sows
regardless of PST injections. Smith et al. (1991) demonstrated
increased weaning weights of pigs only if they were from heavier litters
(averaged g 2.6 kg-pig/BW) on d 7 of lactation when lactating sows were
injected daily from d 7 to d 20 with PST. Weekly injections of PST (70
mg) on d 3, d 10, d 17 and d 24 of lactation does not increase milk
yield or alter the average litter weaning weight (Cromwell et al.,
1989a). In most of the studies, sows injected with PST during lactation
lost more weight and had less backfat than control sows (Cromwell et
al., 1989a; Harkins et al., 1989).

Sow deaths related to PST injections during gestation and lactation
have been noted in several studies. Eighteen out of ninety-eight sows
injected with PST during late gestation and lactation died due to heat
stress (Cromwell et al., 1989b). Trials were conducted from May to
July. Extreme respiratory distress was reported by Kvergas et al.
(1986) just prior to, during or shortly after parturition. Daily
injections of 4, 8 or 16 mg of recombinant PST to lactating sows from d
7 to d 20 caused 6, 20 and 90% mortality , respectively, due to
hemorrhaging of ulcers that developed at the pars esophagea (Smith et
al., 1991). Higher doses of PST had no apparent negative effects in
growing pigs (average BW 50 to 100 kg), suggesting that lactating sows

(average EN 202 to 270 kg) were more sensitive to exogenous PST (Smith

et al., 1991). The majority of the deaths related to PST injections
occurred around farrowing time except in the case of Smith et a1. (1991)
who injected significantly more PST per sow (16 mg'sow"1-d'1 versus 10
mg-sow'l-d'1 or less) than other researchers. Therefore, injecting sows
earlier in gestation and ceasing prior to parturition may not result in
sow deaths to the PST injections.

Growth hormone injections from late gestation through lactation seem
to produce inconsistent results with respect to subsequent increases in
milk production. Day 91 of gestation is the earliest in the allometric
growth phase of the mammary gland that exogenous GH has been
administered to sows thus far. Since the allometric growth phase of the
gestating pig mammary gland begins between d 75 and d 90 of gestation,
it is possible that in the studies conducted previously, injections of
PST were not administered early enough in gestation to achieve the
optimal effect on mammary development. Therefore, it may be possible to
increase mammary secretory tissue by injecting gilts from d 75 of
gestation.

Growth hormone in other species. In cattle and sheep, high dietary
energy and protein decrease serum GH concentrations and mammary growth
(Sejrsen et al., 1983; Johnsson et al., 1985). Prepubertal heifers fed
ad libitum had decreased GH concentrations compared with heifers fed
restricted diets, which was associated with reduced mammary secretory
cell numbers (Sejrsen et al., 1983). Total parenchymal DNA was
positively correlated (r=.40) with plasma GH concentrations while
extraparenchymal adipose tissue was negatively correlated (r . -.53)
with serum GH concentrations. Similar to prepubertal heifers, pregnant

heifers fed ad libitum as compared with those fed moderately during the

isometric (1 year of age to 3 months of gestation) and the allometric (3
months of gestation to 14 d before calving) growth phases of gestation
had lower growth hormone concentrations, although concentrations of IGF-
I were similar during both phases of gestation (Lacrasse et al., 1994).
There were positive relationships between postpartum concentrations of
growth hormone and both peak milk production and feed intake (Lacrasse
et al., 1994). Prepubertal heifers injected with bovine somatotropin
(bST) around puberty (8 months of age) had more parenchymal tissue than
placebo-injected controls (Sejrsen et al., 1986). Furthermore, bST—
injected prepubertal heifers had increased total DNA, total RNA and
RNA/DNA ratios compared with non-injected controls (Radcliff et al.,
1995).

Prepubertal lambs fed restricted diets had higher mean plasma
concentrations of GH and reduced concentrations of prolactin and greater
mammary development, with the impact of feeding level decreasing as age
of the lamb increased (Johnsson et al., 1985). The stimulating effect
of food intake restriction on endogenous secretion of GH declined
markedly with age in the first 20 wk in female lambs. Mammary
parenchymal DNA was positively correlated to mean plasma GH (r = .95)
and the GH:insulin ratio (r = .39) and negatively correlated with the
prolactin:GH ratio (r = -.65) in 20-wk-old lambs (Johnsson et al.,
1986). Prepubertal lambs injected with GH and fed ad libitum had more
parenchymal tissue and parenchymal DNA than those animals on a
restricted diet or fed ad libitum (Johnsson et al., 1986). Growth
hormone injections did not affect the proportions of epithelial,
connective and fat tissues at 20 wk of age (Johnsson et al., 1986). In

another study, prepubertal lambs injected with GH had a greater amount

of parenchymal tissue and parenchymal DNA; however, the differences were
not significant because five out of ten lambs injected with GH died with
no definitive cause of death (McFadden et al., 1990).

From this information, it appears that low GH concentrations decrease
the magnitude of the mammary growth in prepubertal ruminants. In
addition, administration of GH to prepubertal heifers and sheep
increases mammary secretory tissue growth. Akers et al. (1985)
speculated that the effects of GH on mammary growth may be indirect,

mediated through production of somatomedin C by the liver.

WMMW

Swine. Manipulation of the gilt's diet during gestation may affect
mammary secretory tissue growth based on limited studies conducted to
date. In a study conducted previous to the experiments in this
dissertation, excessive dietary energy intake (> 10.0 Mcal ME d'l) in
late gestation was detrimental to the development of mammary secretory
tissue (Weldon et al., 1991) when the results were expressed per number
of functional glands and per kg maternal body weight. Gilts receiving
excessive energy intake had 27% less parenchymal weight, 30% less total
parenchymal DNA, less parenchymal RNA and protein than gilts receiving
adequate energy intake (5.76 Mcal ME/d). In the same study, differences
in dietary protein intake between d 75 and 105 of gestation were not
related to mammary development.

Other species. The relationship between nutrition and mammary growth
has been studied more extensively in species other than swine. It is

important to understand the similarities and differences in mammary

10

development among species to improve our understanding of swine mammary
development.

In rats, cattle and sheep there is a period of prepubertal allometric
growth of the mammary gland (Johnsson and Hart, 1985; Sinha and Tucker,
1969a; Sinha and Tucker, 1969b) which is adversely affected by a high
plane of nutrition (Johnsson and Hart, 1985 and Sejrsen et al., 1982).
The mammary tissue grows at a faster rate than the rest of the body
during the allometric growth phase. Sinha and Tucker (1966) found that
the allometric growth of the rat mammary fat pad occurs 1.56 and 1.96
times faster than body surface area based on total mammary gland fat pad
DNA and specific mammary area, respectively. Cowie (1949) demonstrated
that the rat allometric growth phase could be inhibited by ovariectomy;
therefore, illustrating the necessity of estrogen and progesterone
secretion for the allometric growth phase to occur. Prepubertal mammary
growth has not been studied in swine; however, the prepubertal growth
period in other species is similar to the growth of the pig mammary
gland during late gestation.

Mammary secretory tissue weight and DNA content decreased 23% and 32%
in prepubertal heifers fed ad libitum as compared with prepubertal
heifers fed restricted diets (Sejrsen et al., 1982). In contrast, plane
of nutrition had no affect on postpubertal heifer mammary secretory
tissue growth (Sejrsen et al., 1982). Parenchymal tissue composition
was not altered by plane of nutrition in either the pre- or postpubertal
period. Parenchymal tissue consisted of 10% epithelial cells, 50%
connective tissue, 30 to 40% fat cells and 2 to 3% ductal lumen. In
contrast to restricted versus ad libitum feeding, mammary secretory

tissue growth was similar for prepubertal Holstein heifers fed control

ll

diets ad libitum or fed diets more concentrated in energy and protein ad
libitum (Radcliff et al., 1995). Prepubertal sheep fed a restricted
diet had more total parenchymal tissue and total parenchymal DNA than
lambs fed ad libitum (Johnsson and Hart, 1985; Johnsson et al., 1986).
Lambs fed restricted diets as compared with lambs fed ad libitum had
higher relative growth coefficients for mammary parenchyma, estimated
from the increase in DNA relative to that for live weight, 3.7 versus
2.4, respectively (Johnsson and Hart, 1985). A high plane of nutrition
compared to restricted feeding during the allometric mammary growth
period in prepubertal ruminants has a detrimental effect similar to that
of high dietary energy during the allometric growth phase of the
gestating pig. It is possible that similar mechanisms are involved with
respect to nutrition and it's impact during the allometric growth phase
of the mammary gland in the gestating pig.

A high plane of nutrition fed to heifers during gestation does not
have a negative effect mammary gland development (Harrison et al., 1983;
Valentine et al., 1987) or subsequent milk production (Ducker et al.,
1985; Lacrasse et al. 1993). Harrison et al. (1983) found that mammary
development was not impaired in dairy heifers which were reared rapidly
during pregnancy but were moderately reared prior to one year of age.
Likewise, Valentine et al. (1987) found mammary gland development and
subsequent milk production to be similar in heifers fed 3 planes of
nutrition during the last half of pregnancy. Lacrasse et al. (1993)
reported that milk production in dairy heifers was not affected by plane
of nutrition (ad libitum or moderate feeding (80 and 70% of ad libitum))
fed during the allometric growth phase of the mammary gland during

pregnancy (3 months of gestation to 14 d before calving). Additionally,

12

Ducker et al. (1985) found that heifers fed a high plane of nutrition
during the last 10 weeks of pregnancy had similar milk yields to heifers
fed a lower plane of nutrition. Thus, it seems that there may be
differences in cattle and swine mammary development during gestation
with respect nutritional influences. Specifically, mammary development
in swine may be inhibited by excessive energy intake during late
gestation whereas mammary development is not influenced in cattle fed a
high plane of nutrition during gestation.

Dietary fat. Dietary polyunsaturated fatty acids (PUFA) stimulated
mammary parenchymal development in prepubertal sheep (McFadden et al.,
1990a). Lambs fed a formaldehyde-protected sunflower seed supplement
(by—pass fat, approximately 8.3% sunflower oil) had increased
parenchymal weight and parenchymal DNA compared with lambs fed control
diets without fat additions. In addition, PUFA-fed lambs also had more
extraparenchymal tissue, which could subsequently result in future space
for parenchymal growth to occur. Lambs fed diets with PUFA had twice as
much linoleic acid in the parenchymal lipid compared with lambs which
were not fed diets containing PUFA (McFadden et al., 1990b). Dietary
PUFA increased the number of GH receptors in the liver and the number of
prolactin receptors in the mammary parenchyma. Carrington and Hosick
(1985) have proposed that increases in numbers of receptor sites may
result from increased membrane fluidity caused by higher unsaturated
fatty acid contents. Wahle (1983) demonstrated that accumulation of
unsaturated fatty acids increases membrane fluidity, and Dave and Knazek
(1980) demonstrated that modification of membrane fluidity can alter

hormone binding.

l3

Mammogenesis in mice is increased as a result of feeding dietary PUFA
(Welsch et al., 1985). Mammary gland development increased as dietary
corn oil increased from 0 to 5%. The difference between 5 or 20% corn
oil on mammary gland development was not as great as the difference
between 0 and 5%; however, differences between 5 and 20% corn oil when
comparing whole-mount analyses of mammary glands reached the 7% level of
statistical probability. In-vitro responsiveness of mammary epithelial
area to estradiol and progesterone also increased as the fat content of
the diet increased. The response increased from 5 to 20% but it was not
as pronounced as the increase from 0 to 5%. Therefore, the
responsiveness of the mammary epithelial area to estradiol and
progesterone was greatest when the levels of corn oil supplied provided
adequate essential fatty acids to meet the requirements for essential
fatty acids. There was a linear increase in the number of [3H]-
thymidine-labeled mammary epithelial cells as fat increased from 0 to 5
to 20%.

Diets fed to mice containing 20% coconut oil (92.8% saturated fatty
acids) inhibited growth of normal endogenous mammary epithelial cells
(Carrington and Hosick, 1985). Normal rat mammary and tumorgenic cell
growth in vitro was stimulated by the addition of PUFA whereas the
addition of saturated free fatty acids inhibited cell growth (Wicha et
al., 1979). Linoleic and linolenic acids were the most stimulatory
while stearic acid inhibited cell growth at all concentrations that were
tested. The optimal concentration of unsaturated free fatty acids in
culture roughly paralleled the percentage distribution of these fatty

acids (free plus esterified) in the mammary gland and serum.

14

The effects of PUFA on mammary development in swine has not been
studied to date. Due to similarities which exist between swine mammary
development and mammary development of other species, it is possible
that mammary secretory tissue growth will increase as a result of
feeding dietary PUFA. In addition, dietary PUFA may be synergistic with
exogenous growth hormone on mammary development due to possible
increases in receptor availability for growth hormone.

Soybean oil fed at a rate of 1-5% of the diet is commonly used by
commercial swine producers to improve energy intake in hot weather and
control dust levels in swine facilities. The use of soybean oil for
these practical reasons may also result in increased mammary development

in gestating gilts.

mm

Techniques. Various methods have been used to determine body
composition in pigs. Chemical analysis of the entire ground animal is
the most accurate method; however, it is time consuming, very expensive
and requires killing the animal. The sawdust-residue analysis procedure
was the most accurate technique in growing swine (birth to 145 kg
weight) when compared to using specific gravity or backfat thickness
measurements for prediction of empty body water, protein and fat
(Shields et al., 1983b). The sawdust-residue analysis involves chemical
analysis of the sawdust-residue accumulated from cross-sectional sawing
of the frozen carcass. Similar results were found in reproducing swine
in which the sawdust residue technique was more accurate than the
specific gravity technique to determine carcass or maternal body

composition (Shields and Mahan, 1983). The methods used to determine

15

body composition mentioned thus far are laborious and require death of
the animal. Therefore, these techniques are not suitable to study
changes in vivo body composition. Researchers have developed several
indirect methods to evaluate body composition which do not require
killing the animal, thus these methods are suitable to study in vivo
body composition. The deuterium oxide dilution technique has been used
to estimate in vivo body composition in neonatal pigs (BW = 4 kg),
growing pigs (BW = 7 kg to 145 kg), sexually mature (nongravid) gilts,
and pregnant and lactating sows (Rudolph et al., 1988; Shields et al.,
1983a; Rozeboom et al., 1994; Shields et al., 1984). Shields et al.
(1984) found that predicted fat, ash, protein and water values developed
from maternal body equations were similar to actual values regardless of
stage of pregnancy (d 0, d 57 or d 105). Prediction equations for
protein (R2= .25 and .23, empty body protein and maternal body protein,
respectively) and ash had the lowest accuracy because they involved the
composite error of estimation of the other body components. Rozeboom et
al. (1994) found empty body protein had an R2 of .99 for Yorkshire x
Landrace gilts and .87 for Duroc x (Yorkshire x Landrace) gilts. These
researchers concluded that prediction equations using D20 space, live
weight and backfat thickness were accurate in estimating body
composition of animals only when the equations were derived from animals
that physiologically resembled the population in which the equations
were derived.

Body composition and.mammary development. Relative to body
composition, Head and Williams (1991) and Head et al. (1991) found that
DNA concentrations and estimated mammary cell numbers were less in fat

versus lean gilts at d 112 of gestation. Body weight was similar.

16

Backfat levels were 36 mm and 25 mm for fat and lean gilts,
respectively. Fat gilts had half as many aveolar (milk secretory) cells
as lean gilts based on the numerical density of aveolar cells per gram
of mammary gland. Parenchymal weights and parenchymal fat did not
differ between fat and lean gilts. To summarize, high energy intake
during late gestation, which would lead to fatter gilts, may have a
negative impact on mammary growth in swine. The mechanism by which this

may occur remains unclear.

W

Studies conducted to-date indicate that a high plane of nutrition
during gestation does not influence mammary development in heifers;
however, ad libitum as compared with restricted feeding decreases
mammary growth in prepubertal heifers and sheep. Additionally, elevated
energy intake during late gestation in gilts may be detrimental to
mammary secretory tissue growth which contradicts the findings in
pregnant heifers. The effect of energy intake on gilt mammary
development and potential mechanisms whereby excessive energy intake may
elicit it's response needs to be determined. Two potential mechanisms
whereby excessive energy intake may decrease mammary secretory tissue
growth include decreased GH concentrations and increased body fat.
Exogenous GH administered to ruminants increases mammary secretory
tissue growth. In addition, polyunsaturated fatty acids stimulate
mammary development in other species and may be synergistic with growth
hormone. In conclusion, the effect of energy intake, body composition,
PUFA and growth hormone on mammary development in gestating swine

warrants further research.

CHAPTER 1. EFFECTS OF EEOGENOUS PORCINE SONATOTROPIN AND DIETARY ENERGY
ON NANNARY DEVELOPMENT OF SWINE DURING LATE GESTATION
ABSTRACT

Fifty gilts were used to determine effects of dietary energy and
exogenous porcine somatotropin (PST) on mammary development during late
gestation. Ten gilts were randomly chosen and slaughtered on d 75 of
gestation to describe mammary growth prior to treatment implementation.
On d 75 of gestation, the remaining forty gilts were randomly assigned
in a 2 x 2 factorial arrangement to dietary regimes of adequate (A) or
elevated (E) energy (6.1 or 10.5 Mcal ME/d, respectively) and injections
of 0 or 8 mg/d PST. These gilts were killed on d 105 of gestation.
Total mastectomies were performed on all carcasses following
exsanguination. Mammary tissue was separated into parenchymal (P) and
extraparenchymal stromal (EPS) tissue and analyzed for DNA, RNA, protein
and lipid. Tenth rib backfat on d 105 of gestation was less (P <.05)
for gilts injected with PST regardless of energy level (1.99 cm vs 2.85
cm). There was no effect of dietary energy level or exogenous PST on
number of fetuses; however, average fetal weight was greater (P < .05)
for gilts fed E diets (1.1 kg vs .9 kg). Amount of parenchymal tissue,
total parenchymal DNA, RNA and protein did not differ with dietary
energy level. Neither dietary energy level or exogenous PST influenced
the amount of EPS. However, gilts injected with PST had more (P < .10)
P tissue (1609 9 vs 1963 g). Total parenchymal DNA, RNA and protein
were greater (P < .05) for A gilts injected with PST (4,406 mg, 7,516 mg
and 176 g, respectively) than in A gilts not injected with PST (2,636
mg, 4,250 mg and 105 g, respectively). Feeding elevated energy may have

inhibited the positive effect of PST on mammary secretory tissue growth,

17

18

although how this takes place is unclear at this time. Results of the
present study strengthen the potential for use of PST in commercial
swine production to improve sow milk yields.

Key Words: Swine, Mammary development, Growth hormone

Introduction

Each year greater production demands are put on the sow in commercial
swine production. As producers strive to improve their competitiveness
there is increased pressure on the sow to produce more milk and increase
the kilograms of pigs weaned per sow per year. To maximize milk
production, feeding and management strategies must provide for proper
growth of the mammary gland.

In sheep, cattle and rats there is a period of prepubertal allometric
growth of the mammary gland (Johnsson et al., 1985; Sinha and Tucker,
1969a; Sinha and Tucker, 1969b), which is adversely affected by a high
plane of nutrition (Johnsson and Hart, 1985; Sjersen et al., 1982). In
ruminants, ad libitum as compared with restricted feeding decreases
serum growth hormone (GH) concentrations (Sjersen et al., 1982; Johnsson
et al., 1985). These decreases in GR concentrations are associated with
reduced mammary cell numbers (as measured by DNA content) and a decrease
in subsequent milk production. In prepubertal lambs fed ad libitum
injections of GH restore DNA content of mammary glands to levels similar
to those of animals on a restricted diet (Johnsson et al., 1986). From
this information, it appears that GH concentrations have a positive
effect on the magnitude of the prepubertal mammary gland growth in
ruminants.

Prepubertal mammary growth has not been studied in swine; although,

19

research has been conducted in gestating gilts. Little change occurs in
the DNA content of the mammary gland prior to d 50 of gestation (Hacker
and Hill, 1972). However, DNA concentrations increase four-fold between
d 75 and d 90 of pregnancy (Kensinger et al., 1982). Excess dietary
protein fed to gestating gilts from d 75 to 105 of gestation has no
effect on mammary tissue development while excess energy intake seems to
be detrimental to the development of mammary secretory tissue (Weldon et
al., 1991).

It is possible that GH concentrations and mammary development could
be related in swine, therefore GH may play a role in mammary development
during pregnancy but how is not known. Initial research suggest that
during pregnancy, plasma concentrations of GH remain fairly constant in
swine (Dehoff et al., 1986). The objective of this experiment was to
assess the interaction between dietary energy level and exogenous
porcine somatotropin (PST) on mammary tissue development in pregnant

gilts.

Material and Methods

Animals. Fifty Yorkshire or Yorkshire x Landrace gilts, weighing 161
kg, were initially selected for use in this study. Two gilts were
removed from the study because they were not pregnant, and one gilt died
during the study. Cause of death was unknown. Ten gilts were used to
measure mammary development at d 75 of gestation. After being bred on
their second estrus, gilts (n = 47) were moved into an environmentally
controlled building (minimum temperature 18.3°C, 16 hr light) and housed
in individual stalls (stall size .6 m x 2.1 m). All gilts were fed 1.82

kg/d of a diet formulated to meet NRC (1988) requirements for protein,

20

energy and all other nutrients (designated Adequate energy; Table 1) to
d 75 of gestation.

Treatments. .A 2 x 2 randomized factorial design was employed. Main
effects included either feeding elevated (10.5 Mcal ME/d (El) or
adequate (6.1 Mcal ME/d [A]) dietary energy and injecting gilts with 0
or 8 mg porcine somatotropin (PST), both from d 75 to 105 of gestation.
Desired dietary energy intake was achieved by changing concentrations of
corn and soybean meal, by the addition of cornstarch to the diet, and by
altering feed intake. Daily intake of supplemental vitamins and
minerals was held constant across all treatments. Lysine was held
constant across all treatments by the addition of L-lysine-HCL. PST was
injected immediately following feeding of the gilts. The gilts
receiving 0 mg PST/d were injected with a placebo saline solution.

Slaughter. On d 75 (10 gilts) and d 105 (37 gilts) of gestation,
animals were electrically stunned and exsanguinated. After
exsanguination, total mastectomies were performed and the mammary glands
were immediately frozen in a mixture of dry ice and acetone. Glands
were stored at -20°C until analyses were performed. Individual fetuses
were euthanized, counted and weighed. In addition, hot carcass weight,
backfat and loin eye area at the 10th rib were obtained.

Mammary Dissection and Chemical Analysis. The right side of the
frozen mammary glands was separated into parenchymal (P) and
extraparenchymal stromal (EPS) tissue (Weldon et al., 1991). Tissues
were weighed and stored at -20°C until they were homogenized.

Mammary P and EPS were analyzed for DNA, RNA and lipid content as
described by Tucker (1964). Protein was determined using the method of

Lowry et al. (1951), with bovine serum albumin used as the standard.

21

Statistical Analysis. Data were subjected to ANOVA using the general
linear model of SAS (1985). Due to the presence of interactions (P <
.10) between dietary energy level and PST on the dependent variables,
four conditional contrasts using the Bonferonni t-test, were used to
test treatment effects. The conditional contrast tested the effect of
elevated energy on mammary development (A0 vs E0), the effect of PST on
mammary development for gilts fed diets with adequate energy (A0 vs A8),
the effect of PST on mammary development for gilts fed elevated energy
diets (EO vs E8) and the effect of dietary energy on mammary development
for gilts injected with exogenous PST (A8 vs E8). Interactions did not
exist between dietary energy level and PST with respect to mammary
parenchymal and extraparenchymal stromal tissue; therefore, results were
pooled by main effects rather than using conditional contrasts. Data
reported are least squares treatment means with corresponding

conditional contrasts.

Results and Discussion

Sow Performance. Gilts fed the elevated energy diets were heavier at
the end of the trial (P < .05) and had heavier hot carcass weights (P <
.05; Table 2). Similar to the findings reported by Harkins et al.
(1989) and Cromwell et al. (1989a), tenth rib backfat was less (P < .05)
for gilts injected with PST regardless of energy intake. Weight of
uterus plus conceptus was not affected by dietary energy level or PST
injections; however, there was a tendency (P < .10) for heavier uterine
weights without fetuses for gilts fed adequate energy and receiving PST
as compared with gilts fed adequate energy and receiving placebo saline

injections. There was no effect of dietary energy or PST on number of

22

fetuses or mummified fetuses (10.5, .30 [A0]; 10.7, .33 [E0]; 10.2, .33
[A8]; 9.7, .44 [E8]; SEM = .86 and .20). However, the average fetal
weight (904 g [A], 1,061 g [E]; SEM - 44) was increased (P < .05) by
feeding diets with elevated energy.

mammary development. Characteristics of total mammary tissue of gilts
sacrificed at d 75 and 105 of gestation are listed in Table 3. Gilts
killed on d 75 had less extraparenchymal stromal tissue, parenchymal
tissue, parenchymal DNA, parenchymal RNA and parenchymal protein but had
a greater concentration of parenchymal lipid than gilts killed on d 105
of gestation. This agrees with previous work with pregnant swine
(Hacker and Hill, 1972; Kensinger et al., 1982; Weldon et al., 1991).
On d 105 of gestation, mammary tissue contained more total parenchymal
tissue, DNA, RNA and protein but had a greater concentration of
parenchymal lipid. It is apparent that from d 75 to 105 of gestation
there is a dramatic increase in milk secretory tissue capacity.

Mammary extraparenchymal stromal weights (656 vs 651 g; SEM = 61)
were not different (P > .10) for gilts fed adequate energy diets as
compared with gilts fed elevated energy diets from d 75 to 105 of
gestation. Likewise, mammary parenchymal weight (1820 9 vs 1753 9; SEM
= 136) was not different (P > .10) for gilts fed adequate energy diets
as compared with gilts fed elevated energy diets from d 75 to 105 of
gestation. These results contradict those of Weldon et al. (1991) who
found that gilts fed diets with adequate energy levels had increased
parenchymal weights and similar extraparenchymal stromal weights
compared with gilts fed elevated energy diets. Compared with placebo-
injected controls, gilts injected with PST had more (P < .10)

parenchymal tissue (1609 9 vs 1963 9; SEM = 136.5) while

23

extraparenchymal stromal weight (612 9 vs 695 9; SEM = 42.5) did not
differ (P > .10).

The effect of dietary treatment and PST injections on the amount of
DNA, RNA, protein and lipid, as well as RNA/DNA ratios in parenchymal
tissue are shown in Table 4. Parenchymal lipid was not affected by PST
injections or dietary energy levels (P > .10). In contrast, parenchymal
lipid was decreased in prepubertal sheep fed ad libitum and injected
with exogenous growth hormone compared to sheep fed ad libitum and not
injected with exogenous growth hormone (McFadden et al., 1990).
Parenchymal DNA, RNA and protein, as well as RNA/DNA ratios were similar
for gilts provided with elevated energy as compared with gilts provided
with adequate energy. Thus, contradictory to the results of Weldon et
al. (1991) elevated dietary energy intake in late gestation did not have
a detrimental effect on gilt mammary development. Parenchymal RNA was
greater (P < .10) in gilts injected with PST regardless of dietary
energy level fed.

Various energy x PST interaction were identified. Compared with
placebo-injected controls fed adequate energy diets, gilts injected with
PST and fed adequate energy diets had more (P < .05) parenchymal DNA and
protein. Additionally, parenchymal DNA was higher (P < .10) in PST-
injected gilts fed adequate energy diets as compared with PST-injected
gilts fed elevated energy diets. Although, PST increased mammary
secretory tissue in gilts fed adequate energy diets, feeding elevated
energy diets seemed to inhibit the positive effect of PST. The
mechanism by which this took place is unclear at this time and warrants
further studies to determine the mechanism whereby excess energy is

exerting it's influence. Based on the mammary growth data from this

24

experiment, the present NRC (1988) recommendations for dietary energy
seem satisfactory for gilts injected with PST from d 75 to d 105 of
gestation.

Little is known about the effect of exogenous growth hormone on
porcine mammary development. However, the increase in parenchymal
weight, DNA, RNA and protein found in the present study are similar to
the observations found in prepubertal sheep (Johnsson et al., 1986;
McFadden et al., 1990) and prepubertal heifers (Sejrsen et al., 1986;
Radcliff et al., 1995) injected with exogenous growth hormone.

In the present study, mammary secretory tissue growth was similar (P
> .10) for gilts fed adequate or elevated energy diets from d 75 to d
105 of gestation when the results were expressed on a total basis, or
corrected for number of teats and kg maternal BW. In contrast, Weldon et
al. (1991) found that feeding elevated energy diets during the same
period was detrimental to mammary development. Gilts in both the
present study and that of Weldon et al. (1991) were housed in similar
environments, fed similar diets and were from similar genetic
backgrounds. Body weight of gilts used in the present study were
lighter than those gilts used by Weldon et al. (1991). Although not
known for sure, it is possible that differences in body fat between
gilts in these studies altered the response to differing dietary energy
levels. Head and Williams (1992) found that fat versus lean gilts had
reduced numbers of mammary secretory cells.

Results of Weldon et al. (1991) were expressed on a per teat and per
kg maternal BW basis. This may be another reason for the differences in
results when compared to the present study. Since gilts fed elevated

energy diets were heavier and number of teats were controlled between

25

gilts, this correction may not be valid. Furthermore, gilts were
heavier due to dietary energy intake, thus body weight is confounded
with treatment. We have analyzed the data of Weldon (1988), and
expressed DNA and RNA on a total basis. Total parenchymal DNA, RNA,
protein and lipid were similar (P > .10) for gilts fed adequate and
elevated energy diets. The amount of parenchymal tissue tended (P =
.10) to be less for gilts fed elevated energy diets as compared with
gilts fed adequate energy diets. Thus results from the present study as
well as from Weldon et al. (1991) demonstrate that elevated energy fed
from d 75 to d 105 of gestation is not detrimental to mammary growth
when mammary constituents are expressed on a total basis.

Total EPS DNA and RNA tended (P < .10) to be less in gilts injected
with PST and fed adequate energy diets as compared with placebo-injected
controls fed adequate energy diets (Table 5). Weldon et al. (1991)
reported that EPS DNA and RNA were not affected by dietary energy level.
Likewise, Sjersen (1981) reported that mammary extraparenchymal DNA, RNA
and lipid were not affected by restricted or ad libitum feeding in the
prepubertal heifer. Total EPS protein was greater for gilts fed
adequate energy and injected with PST compared to those gilts fed
adequate energy and receiving placebo injections. Total EPS lipid was
less (P < .05) in gilts injected with PST and fed adequate energy

relative to gilts injected with saline and fed adequate energy diets.

Implications
Injecting gilts with exogenous growth hormone combined with feeding
diets which meet NRC (1988) recommendations for dietary energy (6,100

kcal ME/d) during late gestation enhances mammary growth, which could

26

subsequently lead to increased milk production. Feeding regime or
energy intake seems to be less critical for mammary development and

potential milk production.

27

Table 1. Composition and calculated analysis of experimental

 

 

diets

Ingredient, % Adequate energygfi Elevated energy
Corn 85.05 71.30
Soybean meal (44%) 10.22 2.00
Mono-dicalcium phosphate 1.88 .93
Ground limestone 1.35 .90
Vit-TM premix.a .60 .48
Vit E—Se premix .50 .30
Salt .40 .25
Cornstarch 23.75
L—Lysine HCL .09
Calculated analysis

ME, Mcal/kg 3.2 3.27
Crude protein, % 11.7 6.9
Lysine, % .5 .3
Calcium, % .9 .53
Phosphorus, % .7 .41
Daily intake

Feed, kg 1.90 3.21
ME, Mcal 6.1 10.5
Crude protein, 9 228 228

L sine, g 9.50 9.63

 

Concentration per kg premix: vitamin A, 661,380 IU; vitamin D,
132,276 IU; menadione, .66g; riboflavin, .669; niacin, 3.539; d-
pantothenic acid, 2.64 g; choline chloride, 88.18 g; vitamin 812, 3.96
m ; zinc, 7.5 g; iodine, .11 9; copper, 2 9; iron, 12 9.

Concentration per kg premix: vitamin E, 3310 IU; selenium, 19.8 mg.

28

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29

gilts at d 75 or 105

 

 

ofgestation
Item d 75 so d 1053 so
Number of gilts 10 37
Average wt, kg 155 15 161 13
Extraparenchymal stroma, g 57 20 93 24
Parenchyma
Weight, g 102 248 249 69
DNA, mg/g .7 . 1.9 .2
Total DNA,mg 73 53 476 181
RNA, mg/g 1.2 . 3.3 1.0
Total RNA, mg 130 56 831 386
Protein, mg/g 42 12 76 14
Total protein, 9 5 2 20 8
Lipid, mg/g 609 125 350 97
Total lipid, g 61 9 83 18

 

5Mean of all treatment groups.

30

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CHAPTER 2. DIETARY SOYBEAN OIL DOES NOT INFLUENCE NANNARY DEVELOPMENT OF

GILTS WHEN FED FROM DA! 75 TO DAY 105 OF GESTATION

ABSTRACT

Twenty-seven pregnant gilts were used to determine if supplemental
polyunsaturated fat fed during late gestation influences mammary
development. On d 75 of gestation, gilts were randomly assigned to
either a corn-soybean meal control diet with 0% added soybean oil or a
corn-soybean meal diet containing 5% added soybean oil. Animals in both
treatments received 6.1 Mcal ME, 244 g crude protein, and similar
amounts of lysine, vitamins and minerals daily. On d 105 of gestation,
gilts were slaughtered and total mastectomies were performed. Right-
side mammary tissue was separated into parenchymal and extra-parenchymal
stromal tissue. Parenchymal tissue was weighed and analyzed on a wet-
tissue basis for DNA, RNA, water, protein and lipid. Students t-test
was used to detect treatment differences. Parenchymal tissue water
tended to be less (P = .09) for gilts fed 5% soybean oil. Parenchymal
weight, DNA, RNA and protein were not altered (P > .10) by feeding 5%
soybean oil. The number of fetuses (P > .10) and fetal weights (P =
.09) were similar regardless of soybean oil level fed to the gilts.
Dietary soybean oil did not affect mammary development of gilts when fed
at 5% of the diet from d 75 to 105 of gestation.

Key Words: Swine, Mammary development, Soybean oil

32

33

Introduction

Maximum litter size and weaning weights are dependent on the sow's
ability to secrete milk. Therefore, as producers strive to increase the
number of pigs and pounds of pigs weaned per sow per year, there is
increased pressure on the sow to produce more milk. To maximize milk
production of the sow, feeding strategies must be employed which ensure
optimal mammary gland development of the gilt.

The mammary gland consists of parenchymal tissue (milk secretory
tissue) and extra-parenchymal tissue (primarily fat and connective
tissue). Amounts of parenchymal deoxyribonucleic acid (DNA) and
ribonucleic acid (RNA) can be used as indicators of mammary development
and growth. The amount of DNA is used to assess milk secretory cell
number and may be an indicator of subsequent milk production. The
amount of RNA is an indicator of the functional state of mammary
secretory cells. The RNA to DNA ratio is an indicator of the capacity
of the cells to produce protein. Prior to d 50 of gestation, little
change occurs in the DNA content of the mammary gland (Hacker and Hill,
1972). However, DNA concentrations increase 4-fold between d 75 and 90
of pregnancy (Kensinger et al., 1982). Therefore, late gestation
appears to be the critical period of mammary development.

Mammary parenchymal growth is stimulated in mice and sheep by feeding
diets containing high concentrations of polyunsaturated fats (McFadden
et al., 1990; Welsch et al., 1985), whereas parenchymal growth is
inhibited in mice and rats fed diets containing high concentrations of
saturated fats (Wicha et al., 1979; Carrington and Hosick, 1985; Welsch,
1987). The effect of dietary polyunsaturated fat on mammary development

in swine has not been reported.

34

Soybean oil (830) contains 79.5% unsaturated fatty acids of which
61.5% are polyunsaturated fatty acids (Maynard et al., 1979). It is
commonly used by commercial swine producers at 1 to 5% of the diet to
improve energy intake in hot weather and to reduce dust levels in swine
facilities. In the present study, 5% soybean oil was added to the diet
from d 75 to 105 of gestation to determine if polyunsaturated fat

influences mammary development in gilts.

Materials and.lbthods

General Procedure. A completely randomized block design with 14
gilts per treatment was used. All gilts (initial average weight 155 i 3
kg) were F1, crossbred Yorkshire x Landrace or at least half Yorkshire
with a minimum of 12 functional teats. Relocation was used to stimulate
and synchronize estrus among gilts. Gilts were bred by natural service
on two consecutive days when they expressed estrus following the
location change. Day 0 of gestation was considered to be the first day
of mating. Gilts were housed in individual stalls (stall size = .6 m x
2.1 m) following d 2 of mating in an environmentally controlled (minimum
temperature = 18.3°C, 16 h light) building for the remainder of the
trial and fed a fortified corn-soybean meal diet formulated to meet NRC
(1988) requirements for all nutrients from d 0 to d 75 of gestation
(Table 6, Control diet). Beginning on d 75 of gestation, gilts were
assigned to experimental diets. Experimental diets contained either 0
or 5% soybean oil (880) and were formulated so that animals in both
treatment groups received similar daily intakes of metabolizable energy,
crude protein, lysine, vitamins and minerals (Table 6). One gilt was

removed from the study because she was not pregnant.

35

Slaughter. Gilts were slaughtered on d 105 of gestation at the
Michigan State University Meats Laboratory, under USDA supervision,
according to standard operating procedures. Immediately after
exsanguination, mammary glands, uterus, and fetuses were removed and
weighed. Mammary glands were quickly frozen in a mixture of acetone and
dry ice and stored at -20°C until analyzed. In addition, hot carcass
weight, backfat and loin eye area at the 10th rib were obtained.

Laboratory.Analyses. Mammary glands were dissected into parenchymal
and extra-parenchymal stromal tissue (Weldon et al., 1991). Parenchymal
DNA, RNA, and lipid content were determined according to methods
described by Tucker (1964), and protein was determined by the method of
Lowry et al. (1951).

Statistical Analysis. Analysis of variance using the general linear
model of SAS (1985) was used to test the effect of dietary SEC on
mammary development. Students t-test was used to detect mean

differences.

Results and Discussion

The live weight of gilts at d 105 of gestation did not differ (P >
.33) for gilts fed 0 or 5% SEC, 165 kg vs 170 kg; SEM - 4, respectively.
Carcass weight (95 kg vs 98 kg; SEM = 2.1), loineye area (41.4 cm2 vs
42.4 cmz; SEM = 1.5) and 10th rib backfat (2.15 cm vs 2.14 cm; SEM =
.19) likewise were not different (P > .10) for gilts fed 0 or 5% SEC,
respectively. Regardless of dietary treatment, gilts had similar (P =
.09) numbers of fetuses and fetal weights (Table 7). The similarity in
gilt carcass composition and fetal numbers between treatments was not

surprising because daily consumption of energy, lysine and protein were

36

also similar between treatments.

Parenchymal tissue weight, DNA, RNA and protein were not changed by
feeding 5% SEC (Table 8). Parenchymal tissue water tended to be less (P
< .10) for gilts fed 5% SEC. The lack of difference in parenchymal
tissue weight, DNA, RNA and protein between gilts fed 0 or 5% $80 is not
consistent with studies in mice (Welsch et al., 1985) and sheep
(McFadden et al., 1990) which had increased parenchymal tissue weights
and parenchymal DNA when fed polyunsaturated fat. However, this
inconsistency may be related to species differences, the type of fat fed
as well as differences in dietary energy intake that existed between
experiments. It is possible that PUFA might increase mammary secretory
tissue in gestating swine if the PUFA were fed at higher levels or was a
greater percentage of the total energy intake than existed in the
current study. Diets fed to mice contained corn oil which was added at
the expense of carbohydrate (sucrose), resulting in differences in daily
caloric intake between treatments (Welsch et al., 1985). Diets fed to
sheep, containing sunflower oil, were isocaloric and isonitrogenous, but
daily feed consumption differed among treatments, resulting in
differences in energy intake (McFadden et al., 1990). It is also
possible that $30 was not fed over a long enough period of time to
elicit a response in mammary development. Carrington and Hosick (1985)
proposed that increased deposition of unsaturated fatty acids may unmask
hormone receptor sites through increased membrane fluidity, it is
possible that the PUFA in this study were not fed long enough for this
to occur. Feeding PUFA over a longer period of time may also result in
higher concentrations of lipid-derived stimulatory factors, such as

prostaglandins, which may also influence mammogenesis (Welsch, 1987).

37

Implications
Supplemental dietary polyunsaturated fat (soybean oil) does not affect
mammary development of gilts when fed at 5% of the diet from d 75 to 105 of
gestation. Thus, using 5% dietary soybean oil to improve environmental
conditions in swine facilities or increase dietary energy should not impair or

improve subsequent milk production.

38

Table 6. Composition and calculated analysis of experimental

 

 

diets

Ingredient, % Control Soybean oil
Corn 82.80 74.40
Soybean meal (44%) 12.65 15.85
Mono-dicalcium phosphate 1.85 2.00
Ground limestone 1.30 1.35
Vit-TM premixa .60 .60
Vit E-Se premixb .30 .30
Salt .50 .50
Soybean oil .00 5.00
Calculated analysis

ME, Mcal/kg 3.2 3.4
Crude protein, % 12.6 13.3
Lysine, % .56 .64
Calcium, % .88 .93
Phosphorus, % .70 .73
Daily intake

Feed, kg 1.97 1.86
ME, Mcal 6.1 6.1
Crude protein, 9 245 244
Lysine, g 10.95 11.65

 

Composition per kg premix: vitamin A, 661,380 IU; vitamin
D, 132,276 IU; menadione, .66 g; riboflavin, .66 g; niacin,
3.53 g; d—Bantothenic acid, 2.64 g; choline chloride, 88.18 g;
vitamin B1 3.96 mg; zinc, 7.5 g; iodine, .11 9; copper, 2 9;
iron, 12 9.

Composition per kg premix; vitamin E, 3,310 IU; selenium,
19.8 mg.

39
Table 7. Effect of soybean oil on fetal and gilt mammary

 

 

 

characteristics
Soybean oil, %
0 5

Item (n = 14) (n a 13) SEM P value
No. of fetuses 9.40 9.90 .55 .54
Fetus wt, kg 1.08 1.00’ .03 .09
No. of mummies .08 .14 .09 .60
No. of teats

Right 6.85 6.79 .18 .81

Left 7.00 7.14 .15 .51
Total udder wt, 9 5859 5483 326 .41

Parenchymal wt, 9a 1306 1237 93 .93

Extraparenchymal, 9b 609 679 47 .30
Utero placental full wtC 19.2 18.5 .97 .58
Utero placental empty wtd 10.1 9.7 .5 .63

 

Based on right side mammary glands, weight of secretory tissue minus
skin, muscle and lymph nodes.

Based on right side mammary glands, weight of nonsecretory tissue
minus skin, muscle and lymph nodes.

CWeight including fetuses and fluid.

Weight minus fetuses and fluid°

 

40

Table 8. Composition of mammary parenchymal tissue in gestating gilts
fed diets with soybean oila

Soybean oil, %

 

 

0 5

Item (n = 14) (n - 13) SEM P value
Wt, g 1306 1237 93 .59
Fat, % 28.9 32.4 1.7 .16
Water. % 59.1 55.7 1.4 .09
Protein, mg/g 81.5 79.3 3.4 .64
DNA

#9/9 2084 2060 152 .91

mg 2594 2485 168 .64

mg/teat 373 350 26 .52
RNA

#9/9 3281 3438 236 .64

mg 4251 4187 376 .90

mg/teat 610 591 55 .80
RNA/DNA 1.6 1.7 .12 .84

 

5Based on right side teats associated with secretory tissue.

CHAPTER 3. NUTRITION. BODY TISSUE ACCRETION AND MAMMARY DEVELOPMENT IN
PREGNANT GILTS

ABSTRACT

Thirty-four pregnant Hampshire x (Yorkshire x Landrace) gilts were
used to determine if dietary energy intake and body composition changes
in late gestation (d 75 to 105) were related to mammary development.
Gilts were provided one of two energy intakes (6.1 [Adequate] or 10.5
[Elevated] Mcal ME/d) over two periods (d 0 to 74 and d 75 to 105 of
gestation). Two periods were used to achieve body compositional
differences at d 75 and d 105, and differences in body tissue accretion
rates between d 75 and d 105 of gestation. Empty body composition was
estimated using BW, day of gestation and deuterium oxide space as
predictor variables in equations developed for this experiment. On d 0,
23, 40, 75, and 105 of gestation, gilts were slaughtered and total
mastectomies were performed. Right-side mammary tissue was separated
into parenchymal and extra-parenchymal stromal tissue. Parenchymal
tissue was weighed and analyzed for total DNA, RNA protein and lipid.
Analysis of variance was carried out using the GLM procedure of SAS to
determine the effect of dietary energy level from d 0 to 74 of gestation
and from d 75 to 105 of gestation on mammary development. Parenchymal
tissue DNA (3428 mg vs 3199 mg; SEM = 195), RNA (7494 mg vs 6478 mg; SEM
= 479) and protein (132 9 vs 116 9; SEM = 13.2) on d 105 of gestation
for gilts fed adequate and elevated energy, respectively, were not
related (P > .10) to dietary energy level fed regardless of the
gestational period that it was fed. Parenchymal lipid (389 9 vs 507 9;
SEM . 29.6) was increased (P < .001) at d 105 of gestation when gilts

were fed elevated energy diets from d 0 to d 74 of gestation regardless

41

42

of the level of energy fed from d 75 to d 105 of gestation. Empty body
fat from the four treatment groups ranged from 40.7 to 47.9 kg and 44.4
to 52.6 kg on d 75 and 105, respectively. Empty body protein from the
four treatment groups ranged from 23.7 to 26.4 kg and 28.3 to 30.9 kg on
d 75 and 105, respectively. Between d 75 and 105, gilts gained 3.16 to
7.74 kg of fat and 3.25 to 5.70 kg of protein. Regression analysis was
used to evaluate the relationship between body composition changes and
mammary development. DNA and RNA on d 105 were not related (P > .10) to
empty body fat or protein on d 75 or 105, or to changes in empty body
fat or protein from d 75 to 105. In conclusion, elevated dietary energy
intake from d 0 to d 74 of gestation or from d 75 to 105 of gestation
did not affect mammary secretory tissue growth. The gilts ability to
milk in her first lactation was not related to body compositional
changes occurring in late gestation.

Key Words: Swine, Gilt, Mammary development, Body composition

Introduction

The goal to increase sow productivity continues to be a high priority
in commercial swine production. To increase the number of pigs weaned
per sow per year and litter weaning weights, the sow must produce more
milk. The association between nutrition and growth of milk secretory
tissue during gestation is not well understood and must be, in order to
maximize milk production in the sow.

Parenchymal deoxyribonucleic acid (DNA)is an indicator of mammary
secretory cell number. Ribonucleic acid (RNA) is a reflection of the
functional state of the cell, and the RNA/DNA ratio is an indicator of

protein synthesis activity per cell in the mammary gland. Little change

43

occurs in the amount of DNA in the mammary gland prior to d 50 of
gestation (Hacker and Hill, 1972). Mammary DNA concentrations increase
fourfold between d 75 and 90 of gestation (Kensinger et al., 1982).
Excessive dietary energy intake (> 10.0 Mcal ME/d) in late gestation was
shown to be detrimental to development of mammary secretory tissue in an
experiment by Weldon et al. (1991). In a subsequent study however,
there was no detrimental effect on mammary development when gilts were
fed excessive energy in late gestation (Howard et al., 1995 companion
paper see Chapter 1).

In experiments conducted by Weldon et al. (1991) and Howard et al.,
(1995 companion paper see Chapter 1), gilts were housed in similar
environmental conditions, provided with similar nutrient intakes daily
and selected from a similar genetic pool of animals. However, in the
second study gilts were heavier on d 75 of gestation and subsequently
may have been fatter than gilts in the first study. It is possible that
differences in body composition among gilts when entering late gestation
influenced the mammary growth response to excessive dietary energy
intake. Our objective was to determine if dietary energy intake or body
composition changes during gestation influence total mammary secretory

tissue development in the gilt.

Materials and Methods
Animals. Forty Hampshire x (Yorkshire x Landrace) gilts (average
weight 117 kg, average backfat depth 20.6 mm) with a minimum of 12
functional teats were selected initially. Gilts were checked for estrus
two times per day and bred naturally on their second estrus using year-

old Hampshire boars. Matings were permitted every 12 h for a maximum of

44

three times. The first day of mating was considered d 0 of gestation.
Following breeding, gilts were moved into an environmentally controlled
(minimum temperature = 18.3° C, 16 h light) building and housed
individually (stall size = .6 m x 2.1 m). Gilts were of similar ages
(average 218 d i 12 d) to remove any possible age effect. Six gilts
were removed from the study because they were not pregnant; therefore,
34 gilts were eventually used.

Treatments. A randomized design was used with a 2 x 2 factorial
arrangement of treatments. Ten gilts were assigned to each treatment
initially. The main effects included gestational period (d 0 to d 74
[P1] or d 75 to d 105 [P2]) and dietary energy level, either adequate
energy (6.1 Mcal ME/d, [A]) or elevated energy (10.5 Mcal ME/d,[E]).
Dietary energy level was altered by changing concentrations of corn and
soybean meal, adding cornstarch to the elevated energy diet and changing
the daily allotment of feed per gilt (Table 9). Daily intake of
supplemental vitamins, minerals and lysine were held constant across all
treatments and met NRC requirements (1988).

Body COmposition. Amounts of body fat and protein on d 75, d 105 and
changes occurring from d 75 to d 105 of gestation was varied by
providing adequate or elevated amounts of dietary energy from d 1 to d
74 and d 75 to d 105 of gestation. Empty body composition of all gilts
at d 75 and 105 of gestation was estimated using the deuterium oxide
(DZO) dilution method as described by Shields et al. (1984) and Rozeboom
et al. (1994). Prediction equations (Table 10) were developed
specifically for this population of gilts. Animals were slaughtered and
chemically analyzed at various stages of gestation, d 0 (n = 7), d 23 (n

= 3), d 40 (n = 2), d 75 (n = 6) and d 105 (n = 7). Carcass, viscera,

45

uterus with fetuses and blood samples were analyzed in triplicate for
moisture (oven drying), ether extract (Soxhlet apparatus), protein
(Kjeldahl method, AOAC, 1980) and ash (AOAC, 1980). Appropriate
procedures (Rozeboom et al., 1993) were followed to collect measurements
used in body composition determinations.

Body composition equations were developed on both an empty body and
maternal body basis. Empty BW was calculated by subtracting digesta
from live weight (Shields et al., 1984 and Rozeboom et al., 1994).
Maternal BW was calculated by subtracting digesta and uterus with fetus
from live weight (Shields et al., 1984).

Mammary Growth. To assess mammary growth gilts were slaughtered on d
0 (n = 10), d 23 (n a 3), d 40 (n = 3), d 75 (n = 7) and d 105 (n = 34)
of gestation at the Michigan State Meats Laboratory, under USDA
supervision, according to standard operating procedures. All of the
gilts slaughtered for body composition prediction were also used to
evaluate mammary development. Immediately after exsanguination, mammary
glands, uterus and fetuses were removed and weighed. Right side mammary
glands were quickly frozen in a mixture of acetone and dry ice and
stored at ‘20°C until analyzed. The number of corpora lutea were
counted and recorded for both ovaries.

Right side mammary glands were dissected into parenchymal and
extraparenchymal stromal tissue (Weldon et al., 1991). Parenchymal DNA,
RNA and lipid were determined according to Tucker (1964), and protein
was determined by the method of Lowry et al. (1951) for gilts
slaughtered at d 105 of gestation. Prior to d 105 of gestation the

right side mammary glands were only analyzed for parenchymal weight,

46

parenchymal protein, parenchymal lipid, parenchymal water and
extraparenchymal weight.

Constituents of mammary tissue were expressed on four different bases
in the tables: 1) concentration, 2) total, 3) corrected for the number
of teats associated with secretory tissue and 4) corrected for the
number of teats associated with secretory tissue and kg maternal BW
(live weight minus fetal weight).

Statistical Analysis. Analysis of variance was carried out using the
general linear model procedure of SAS (1986) to determine the effect of
dietary energy level and the gestational period in which the dietary
energy level was fed on mammary development. The interaction between
dietary energy level and gestational period was included in the model.
Pair-wise t-tests were used to detect differences between treatments.

Linear regression models predicting empty and maternal body
components using all combinations of independent variables (DZO space,
BW, day of gestation, and backfat depth) were fitted using SAS (1986)
procedures. Selection of variables for inclusion in prediction models
followed criteria described by Rozeboom et al., 1994.

Regression analysis (SAS, 1986) was used to determine if mammary
parenchymal DNA and RNA on d 105 of gestation were related to changes in

body composition occurring during late gestation.

Results and Discussion
Body Composition Prediction Equations. Equations for estimating body
composition for this population of gilts were developed with good
prediction accuracy. Rozeboom et al. (1994) found EBPRO and EBFAT had

R2 values of .99 and .96 for Yorkshire x Landrace gilts and .87 and .97

47

for Duroc x (York x Landrace) gilts, respectively. The equations
developed by Shields et al. (1984) had R2 values of .35 and .86 for
EBPRO and EBFAT, respectively. The equation developed in this study for
empty body protein (R2 = .66) was not as powerful as that developed by
Rozeboom et al. (1994) but more powerful than that of Shields et al.
(1984). Furthermore, the equation developed in this study for empty
body fat (R2 = .95) was as powerful as that developed by Rozeboom et al.
(1994) and more powerful than that of Shields et al. (1984).

Growth Performance and Body COmposition. During P1 gilts fed elevated
energy compared with gilts fed adequate energy were heavier, had more
backfat, EBFAT (P < .01) on d 75 and on d 105 of gestation and EBPRO (P
< .10) on d 75 of gestation (Table 11). Gilts provided with elevated as
compared with adequate dietary energy intake during P2 regardless of
dietary energy intake during P1 were heavier, had more EBFAT (P < .01)
and tended (P < .10) to have more EBPRO on d 105 of gestation.
Interactions did not exist between period and dietary energy level on d
105 of gestation for gilt BW, backfat or empty body composition (P >
.10), therefore the response to energy intake in P2 was not dependent on
energy intake in P1.

Change in EBFAT from d 75 to 105 of gestation was influenced (P <
.01) by energy intake from d 0 to 74 of gestation. More specifically,
change in EBFAT between d 75 and 105 of gestation was less (P < .05) for
gilts with elevated dietary energy intake during P1 and greater (P <
.01) for gilts fed elevated energy diets during P2. EBFAT at d 105 of
gestation increased 214% for gilts fed adequate energy during P1 (7.18
kg vs 3.36 kg) but only 143% for gilts fed elevated energy during P1

(4.76 kg vs 3.33 kg) when gilts were fed elevated energy diets during

48

P2. Change in EBFAT from d 75 to 105 of gestation was similar for gilts
fed adequate energy diets during P2 regardless of diet fed during P1
(3.36 kg vs 3.33 kg). There are a couple of reasons why these results
were observed. First, the gilts provided with adequate energy during P1
were lighter (157 kg vs 181 kg) at d 75 of gestation than gilts provided
with elevated energy. Thus, these gilts would require less maintenance
energy and may have also utilized energy more efficiently in P2.
Subsequently, when both groups were switched to elevated energy diets
during P2, the gilts fed adequate energy during P1 had greater fat
accretion rates during P2 compared with gilts provided with elevated
energy intake during P1. Secondly, since the majority of fetal growth
occurs during late gestation, more energy would be utilized for fetal
growth as compared with maternal deposition during late gestation.
Reproductive measurements. Gilts fed elevated energy diets during P1
had a greater (P < .05) number of fetuses compared to gilts fed adequate
energy diets during P1 (Table 12). Results from a previous study
indicate that conspectuses may stimulate mammary development (Kensinger
et al., 1986) if differences are extreme (S 4 versus 2 11). The
difference among treatment groups in the present study was only 2 pigs.
Thus, fetal number differences in the present study are not thought to
have affected overall mammary growth. Fetal weight was similar across
treatments. The numbers of corpora lutea did not differ among
treatments; consequently, percent survival was higher (P < .05) in gilts
fed elevated energy compared to gilts fed adequate energy during P1.
Mammary development. Mammary development at d 0, d 23, d 40 and d 75
of gestation was characterized by evaluating mammary glands from gilts

slaughtered for development of body composition prediction equations.

49

The mammary glands were analyzed only for amount of extraparenchymal
tissue, parenchymal tissue, parenchymal protein, parenchymal fat and
parenchymal water. Parenchymal tissue weight did not change from d 0 to
d 40 of gestation, but it increased (P < .01) 63 percent by d 75 of
gestation (Table 13). Similarly, total parenchymal tissue water and
protein were greater (P < .01) at d 75 of gestation than at d 0, d 23 or
d 40 of gestation whereas total parenchymal fat did not change between d
0 and d 75 of gestation. Parenchymal DNA and RNA at d 75 were not
measured in this study. However, a positive relationship at d 105 of
gestation was identified between parenchymal DNA and RNA and parenchymal
weight (R2 - .81; .80) and protein (R2 - .78; .83) shown in Table 14.
Thus, based on the assumption that the same relationship occurs at d 75
of gestation between parenchymal DNA and RNA and parenchymal protein and
parenchymal weight, it is likely that parenchymal DNA and RNA were also
increased at d 75 of gestation. Hacker and Hill, (1972) found minimal
changes in the amount of DNA and RNA in the gilt mammary gland during
the first 50 days of pregnancy, whereas between the 50th and 100th days
of pregnancy the amount of parenchymal tissue, parenchymal DNA and
parenchymal RNA were increased dramatically. Kensinger and coworkers
(1982) found that although concentration of mammary DNA numerically
increased from d 0 to 30 and d 45 of gestation, the change was not
statistically significant. However, between d 75 and 90 of gestation
mammary DNA increased significantly. Ribonucleic acid continued to
increase from d 90 of gestation through d 4 of lactation. The previous
studies support the findings in this study that there is minimal growth

of the mammary gland prior to d 75 of gestation.

50

Mammary parenchymal weight and protein increased by d 75 of
gestation; however, the magnitude of increase was small in comparison to
the increase in parenchymal weight (68%) and protein (626%) by d 105 of
gestation. The increase in mammary growth from d 75 to 105 of gestation
is in agreement with Weldon et al. (1991) and Howard et al. (1992) who
found that the majority of mammary growth occurs between d 75 and 105 of
gestation.

Since the majority of mammary secretory tissue growth during
gestation occurs between d 75 and d 105, it is not surprising that
feeding elevated energy from d 0 to d 74 of gestation does not influence
the amount of parenchymal tissue or parenchymal tissue composition on d
75 of gestation. Feeding elevated versus adequate dietary energy to
gilts from d 0 to 75 of gestation increased (P < .01) extraparenchymal
tissue weight (814 9 vs 367 9; SEM = 54) without affecting (P > .10)
parenchymal tissue weight (698 9 vs 591 9; SEM = 64), parenchymal tissue
water (225 9 vs 237 9; SEM = 28), parenchymal tissue fat (433 9 vs 321
9; SEM = 50) or parenchymal tissue protein (35.8 9 vs 31.7 9; SEM = 3.6)
on d 75 of gestation.

Gilts were provided with adequate or elevated dietary energy intake
over two periods to determine the influence of energy intake during late
gestation on mammary growth at d 105 of gestation. The amount of
extraparenchymal tissue and parenchymal fat were increased (P < .01) in
gilts provided with elevated energy as compared with gilts provided with
adequate energy intakes during P1 (Table 15). However, the amount of
parenchymal tissue, extraparenchymal tissue, parenchymal fat and
parenchymal protein were not different (P > .10) among gilts provided

with elevated energy intake compared with gilts provided with adequate

51

energy intakes during P2 (Table 15). Total parenchymal DNA and RNA did
not differ with dietary energy level fed, regardless of the gestational
period in which it was fed (Table 16). Therefore, gilts provided with
excessive energy intake (10.5 Mcal/d) from d 0 to d 74 or d 75 to d 105
of gestation had similar mammary secretory tissue growth as gilts
provided with adequate energy intake (6.1 Mcal/d) during the same
periods. These findings contradict those of Weldon et al. (1991) who
found that gilts fed elevated energy diets from d 75 to 105 of gestation
had decreased parenchymal DNA and RNA compared with gilts fed adequate
energy diets. However, Weldon et al. (1991) corrected parenchymal DNA
and RNA results for the number of functional glands (teats associated
with secretory tissue) and per kg maternal BW. Since dietary energy
influences both BW and mammary growth, BW is confounded with treatment.
In addition, the number of teats in the present study and that of Weldon
et al. (1991) were controlled within experiment (12 to 14 per gilt), so
a statistical correction or adjustment is not necessary. Therefore
presentation and interpretation of mammary growth data on a total basis
is believed to be the most valid. When we expressed the data of Weldon
(1988) on a total basis, the amounts of parenchymal DNA and RNA were not
influenced by dietary energy level in late gestation (P > .10). These
results are now in agreement with similar data collected in the present
study.

Similar to swine, Lacrasse et a1. (1993) found that plane of
nutrition during gestation did not influence milk production in heifers.
Likewise, work with prepubertal heifers by Radcliff et a1. (1995), has
shown that feeding excess energy and protein does not influence

parenchymal DNA, RNA or RNA/DNA ratios. In contrast, however ad libitum

52

as compared with restricted feeding during the prepubertal period has
been shown to be detrimental to mammary growth in sheep and cattle
(Sejrsen et al., 1982; Johnsson and Hart, 1985). Thus, the influence of
nutrition on mammary growth in sheep and cattle is still thought to have
an impact during the prepubertal period on total mammary secretory cell
number.

Parenchymal DNA and RNA at d 105 of gestation were not related (R2 <
.07, P > .10) to EBFAT or EBPRO at d 75 or 105 of gestation or empty
body weight at d 105 of gestation. Also, changes in EBFAT or EBPRO from
d 75 to 105 of gestation were not related (R2 < .04, P > .33) to
parenchymal DNA or RNA at d 105 of gestation. Thus, fat and protein
accretion in gilts from d 75 to 105 of gestation has no detrimental
affect on potential milk yield of the sow. These results contradict
those of Head and Williams (1991) who found that DNA concentrations and
estimated cell numbers were decreased at d 112 of gestation for fat
versus lean gilts of the same BW. The discrepancies between studies may
be attributed to differences in total body fat. Head et al. (1991)
reported backfat thickness of 36 mm and 25 mm, for fat and lean gilts,
respectively. Gilts in this study had backfat thickness of 31 mm and 25
mm for gilts fed elevated and adequate energy diets from d 0 to d 74 of
gestation, respectively. In our study feed intakes by gilts on elevated
energy treatments were maximized therefore it would have been difficult
to achieve greater amounts of backfat and total body fat. Yet, in the
studies conducted by Head et al. (1991) there may have been greater
amounts of body fat which may have had a greater influence on mammary

secretory tissue growth.

53

Implications
Feeding excessive energy during gestation does not influence mammary
secretory tissue growth. Likewise, there seems to be no relationship
between mammary development and body fat or protein accretion rates
between d 75 and 105 of gestation. The period when the majority of
mammary growth occurs in the pig. Thus, feeding excessive energy to

primiparous females during gestation should not impair milk production.

54

Table 9. Composition and calculated analysis of experimental

 

 

diets
Ingredient, % Adequate energy Elevated energy
Corn 85.05 71.30
Soybean meal (44%) 10.22 2.00
Mono-dicalcium phosphate 1.88 .93
Ground limestone 1.35 .90
MSU Vit-TM premixa .60 .48
Vit E-Se premix .50 .48
Salt .40 .25
Cornstarch 23.75
L-Lysine HCL .09
Calculated Analysis
ME, Mcal/kg 3.2 3.27
Crude protein, % 11.7 6.9
Lysine, % .5 .3
Calcium, % 9 .53
Phosphorus, % 7 .41
Daily Intake
Feed, kg 1.94 3.27
ME, Mcal 6.1 10.5
Crude protein, 9 228 228
L sine, g 9.71 9.81

 

 

Concentration per kg premix: vitamin A, 661,380 IU; vitamin
D, 132,276 IU; menadione, .66 g; riboflavin, .66 g; niacin,
3.53 g; d-pantothenic acid, 2.64 g; choline chloride, 88.18 g;
vitamin B1 3.96 mg; zinc, 7.5 g; iodine, .11 9; copper, 2 9;
iron, 12 9.

Concentration per kg premix; vitamin E, 3310 IU; selenium,
19.8 mg.

55

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56

popped pnooom onu mcfinop axons“ Smoocoufiamo common umufim onu mcfiuop oanCH >mwocm
mx.mm<mm

 

 

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mx .u: mpom
mo4Ho mo Ho mm: 1o u no no u so no u no AoH u so smoH
humoum mmwmom mum aum one 4.4

 

 

 

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no uncommon com muamm NON cofiuflmooeoo >UOQ >uoEo pom ummxomn .munmfios Spom .HH manna

57

.mommfiu >u0uouoom sums poumHUOmmo momma moan usmmw mo .ozn
.Ap\mz Hmoz m.oa. Samoan poum>ofio u m .Ac\mz Hmoz H.mv xmuoco oncogene u d
«Ammo cofiuoo pcooom onu moonsp oxmucfi homecouAHmv pofluoo umumu on» mcfluop oxmucfl Smwmcmm

 

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o4. 4H. ea. Hoo.fi m.o o.m m.m o.m mg .msmmflu moose»:
o.mm m.oH m.oH e.oH me .oooam a money

aw. mo. no. bob.v .oommfiu common:

onQEOU ocHuouD

ea. me. mm. omm. o.o o.o o.o o.o nmummo mo .02
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om. om. mo. oo.omm o.Ho o.mo m.mo m.oo » .Hm>o>uom
om. mo. om. omm.o H.HH m.oH o.HH e.mH amuse muoouoo
mm. am. or. mma. H. H. o. m. monsoon

poHMHEESE mo .02

 

 

mm. as. om. omo. H.H H.H H.H o.H as .u3 wanna
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mmaam me do mm: 1o u no A on no no u no nod n no smoH

hummus museum mum «um mac cn<

 

woxmucH amuocm

1:0oumommmmo moH 0» me o one me 06 o no opossum
mcmpomw 03D uo>o >mumco poum>oao no uncommon pom muaflm u0m mucosouommoe o>fluooponoom .NH canoe

58

 

.3ou umnu om poumompcA oomm> m on» >n nouump mzou smsums muomuomuoqom ucouommmomu
.mopoc noezm one odomoe .cme mmom oommmu Snobouoom mo usmmozo
.zm announce mx won Anommmu
>h0uouomm sums poDmHUOmmm mucouv umou anaemuocom nod pommouaxo out some humEEmzp
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.mopoc ndshm one saunas .CHRm mmom common >u0uouoom-coc mo unmmozn
.mocmmm >umEEmE opmm unmmu co pommm

 

 

 

 

 

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COHDMDmom mo xmo
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moo Aosmmmu >u0uouoom sums poumm00mmm mucouv umou HMCOHDUCDM moo pommmuaxo mum comp muoEEmzo
.Ucmmm xunEEmE comm unmmu co pommm
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.uoums Hms>nuconmd .chuouQ Hmexsucoumo humEEmE mo mum Auouuo pumocmum + oumEmumm mowmovm ummma
“any mucomomuuooo one mombmmum> «zm pom <20 munEEmE was > muons .o + mxmb + on a» was Hopozmllu

 

59

 

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.mH wanmh

61

 

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.mpcnmm xuoEEmE 00mm Damon so pommmm

 

 

 

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noxmucH xmuocm

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poum>omo no uncommon pom momma MOM o0mumumom mo mom p on <zm pom £20 oommflu onshconoumm .om oHomB

General Discussion

Milk production is related to the amount of mammary secretory tissue
in rats and heifers. Studies conducted in heifers during gestation
indicate that ad libitum feeding does not influence mammary secretory
tissue growth; however, ad libitum feeding in prepubertal sheep and
heifers decreases mammary secretory tissue growth. Exogenous growth
hormone administered to sheep and cattle increases mammary secretory
tissue growth. Polyunsaturated fatty acids stimulate mammary
development in other species and may be synergistic with growth hormone.
Little research has been conducted on swine mammary development.
Earlier research suggested that elevated energy intake during late
gestation in swine may have a negative influence on mammary secretory
tissue growth. But this conclusion is contested by research conducted
herein. The effects of body composition, PUFA, growth hormone and
energy intake on mammary development in pregnant swine were studied.

Body compositional changes during gestation did not influence mammary
secretory tissue growth. Similarly, feeding PUFA to gilts from d 75 to
105 of gestation did not influence mammary secretory tissue. However,
mammary secretory tissue was increased in PST-injected gilts fed
adequate energy diets. The increase in mammary secretory tissue in PST-
injected gilts fed adequate energy needs to be confirmed along with
subsequent milk production measured for gilts injected with PST during
the same gestational period. If the increase in mammary growth for PST-
injected gilts fed adequate energy can be repeated and excessive energy
intake inhibits the positive effect of growth hormone on mammary

secretory tissue, as shown in experiment one, then the mechanism whereby

62

 

63

excessive energy inhibits the positive effect of growth hormone should
be elucidated.

Weldon et al. (1991) reported that gilts fed diets which provided
10.5 mcal ME/d from d 75 to 105 of gestation had less mammary secretory
tissue as compared with gilts fed diets containing 5.7 mcal ME/d. More
specifically, gilts fed excessive energy had less parenchymal tissue,
parenchymal DNA, parenchymal RNA and parenchymal protein as compared
with gilts fed diets which met the NRC (1988) requirement for energy ‘
when the data were corrected for the number of functional glands and kg
maternal BW. Similarly in the present study, gilts in experiment three,
fed elevated energy diets from d 75 to 105 of gestation, had more
parenchymal RNA-teat'l-kg BW'1 and parenchymal protein teat‘l-kg BW'1
compared with gilts fed adequate energy diets.

We, in experiment three, and Weldon et al. (1991). corrected
parenchymal tissue constituents, such as parenchymal DNA, for the number
of teats (teats associated with secretory tissue) and kg maternal BW.
This correction is believed to be invalid for the following reasons.
First, the number of teats is a selection criteria used in all of the
experiments, thus the number of teats are controlled across treatments.
Secondly, BW is confounded with treatment in that it is influenced by
energy intake; gilts fed excessive energy were heavier (P < .001) as
compared with gilts fed adequate energy (Table 17).

Further evidence that the data need not be corrected for BW is shown
in the regression of BW on parenchymal DNA and RNA for gilts treated
similarly prior to mammary gland analysis. No relationship (R2 = .004)
existed between gilt SW (130 kg to 200 kg) and parenchymal DNA (1000 mg

to 4900 mg) for gilts fed similar diets, illustrated in Figure 1.

64

Heavier gilts will not necessarily have more DNA than lighter gilts
simply because they are heavier.

When the data in experiment three (present study) was expressed on a
total basis rather than correcting for the number of teats and maternal
BW, total parenchymal RNA and parenchymal protein were not influenced by
feeding elevated energy diets. Likewise, when we reanalyzed the data of
Weldon (1988) on a total basis, we found that excessive energy did not
decrease mammary secretory tissue growth. In experiment one (present
study) feeding excessive dietary energy (10.5 mcal ME/d) as compared
with feeding adequate dietary energy (6.1 mcal ME/d) from d 75 to 105 of
gestation did not influence mammary secretory tissue, regardless of how
the data were expressed. Thus, the results from all three experiments
lead to the same conclusion, feeding 10.5 mcal ME/d from d 75 to 105 of
gestation does not impair mammary secretory tissue growth. These
findings are in agreement with studies conducted in prepubertal and
pregnant heifers fed a high plane of nutrition (Radcliff et al., 1995;
Harrison et al., 1983; Valentine et al., 1987). But are in contrast to
conclusions reached in other studies conducted with prepubertal heifers
and lambs (Sejrsen et al., 1982; Johnsson and Hart, 1985).

To further confirm that feeding elevated energy from d 75 to 105 of
gestation does not impair mammary secretory tissue development in swine,
the results from experiment one, experiment three and Weldon (1988) were
pooled and statistically analyzed for differences in parenchymal weight,
extraparenchymal weight, parenchymal DNA, parenchymal RNA, parenchymal
protein and parenchymal fat (Table 17). The model included experiment,
energy intake (adequate or elevated) and the interaction between

experiment and energy intake. Although, most variables tested had

 

65

significant experimental effects (P < .05), dietary energy level did not
influence total parenchymal weight, parenchymal protein, parenchymal
fat, parenchymal DNA, parenchymal RNA or the parenchymal RNA/DNA ratio
(P > .10). The extraparenchymal tissue weight was higher for gilts fed
elevated energy diets as compared with gilts fed adequate energy diets
(P < .10). Results from this combined analysis confirm the conclusion
that mammary secretory tissue is not influenced by feeding elevated
energy from d 75 to 105 of gestation.

To confirm the relationship between mammary development and milk
production in swine, studies need to be conducted in which mammary
development and milk production from the same animals can be correlated.
Subsequent to these studies areas of future research include prepubertal
and hormonal influences on swine mammary development. Since, little is
known about swine prepubertal mammary development and the impact of diet

during this period it is an area which warrants further investigation.

 

66

Table 17. Composition of mammary tissue in gestating gilts fed diets with

adequate or elevated energylevels

Energy level (EL)b

 

 

 

6.100 10.500 P value

Item (n - 31) (n - 23) SEM Expc’ EL ExpssL
Extraparenchymal wt, 9 613 714 35.7 .16 .05 .30
Parenchymal wt, 9 1314 1270 80 .0006 .75 .31
Parenchymal fat

mg/g parenchyma 345 289 25.5 .003 .12 .19
g 470 377 44.9 .0009 .14 .16
g/teat 66.7 53.0 5.65 .0001 .09 .14
g-teat'l-xg and .41 .29 .037 .008 .03 .19
Parenchymal protein

mg/g parenchyma 129 100 21.1 .04 .33 .29
g 180 123 37.3 .32 .28 .20
g/teet 25.0 17.1 4.59 .29 .22 .17
g-teat'lskg W1 .16 .10 .031 .17 .16 .20
Parenchymal DNA

pg/g par-mm 2‘50 2‘77 95.7 .0001 .O‘ .4‘
mg 3089 3048 195.3 .85 .88 .09
mg/teat 448 425 25.5 .68 .51 .08
mg°teat’1°kg aw*1 2.79 2.42 .15 .13 .09 .12
Parenchymal RNA

pg/g pat-anew 4038 3945 110 .0001 .55 .19
mg 4 5195 4916 343 .0001 .56 .16
mg/teat 752 686 43.6 .0001 .28 .19
mg'teat'l-kg aw-l 4.64 3.87 .26 .0001 .04 .24
Parenchymal RNA/DNA 1.69 1.62 .063 .0001 .46 .91

 

Based on right side teats associated with secretory tissue.
bkcal/kg.
cExperimental data pooled from Weldon (1988). experiment 1 and
experiment 3.

 

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