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TWO NEOTROPICAL RODENTS AS
BIOASSAY TEST ORGANISMS

Thesis for the Degree of M. S‘
MICE‘HGAN STATE UNEVERSITY
ANN C. UNE‘ERHELL
1972

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ABSTRACT
3N0 NEOTROPICAL RODENTS AS BIOASSAY TEST ORGANISMB

By
Ann C. Underhill

weanlings of three rodents, Sigmodon fulviventer, §, his idus, and
‘AESQQE.EEEEE2’ were evaluated to determine their usefulness as bioassay
test animals for nutrition studies and the findings compared with those
for Microtus pennsylvanicus which has previously been used.

Experiment I determined that 7% protein, using casein as the
standard, was most efficiently utilized by the animals as shown by the
Protein Efficiency Ratio (PER). Experiment II tested the qualities of
grain proteins from two wheat-rye hybrids (Triticale-MSU #358 and
Triticale-Rockefeller PC70) in comparison with that of casein, all at
the 7% level.

It appears that both species of cotton rats would be highly suitable
as bioassay test mammals. They both responded to protein quality in a
manner similar to 14. mnnsylvanicus. Algo_d9_r_1_ az_arie_ also followed much
the same pattern, except the PER values were somewhat lower in Experiment
I and significantly lower (P) .05) in Experiment II. This could be

partly due to its much smaller size.

TWO NEOTROPICAL RODENTS AS

BIOASSAY TEST ORGANISMS

By

\a
WW -
Ann C. Underhill

A THESIS

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

MASTER OF SCIENCE
Department of Zoology

1972

ACKNOWLEDGMENTS

I am grateful to professors Rollin H. Baker, Martin Balaban and
Fred C. Elliott for their guidance in the research and assistance in
writing this paper.

I am also indebted to Professor Charles Cress for his aid with the
statistical analysis of the data, to Peter Dalby for supplying the
5529229 and to all other graduate students of the MSU Museum for their
patient advice and encouragement. I thank Professor Fred C. Elliott in
addition for providing most of the facilities for the research, for his
guidance in designing the experiment, and for supplying the data on

Microtus pennsylvanicus used in this study.

ii

CONTENTS

ImmmmgouonououououononoHonouonououououououo"
INTRODUCTION ...................................................
Protein Evaluation Tests ..................................
EXPERIMENTAL ...................................................
Test Mammals Used .........................................

MethOdS ...0............0..0.....0....00.......0.00.0......

Experiment I: Determination of most efficiently utilized
level Of casein 0.00....0...................

Experiment II: Comparison of qualities of 3 proteins .....
mSUIITS ..0....0...0..........0.......0.....0...................
ANALYSIS OF DATA AND DISCUSSION . .... O. O. 0.... 0.. .0. ... ..0......

SUM-RY .....0..........0..............0...............0....0...

LIIERAWRE CITED 0....0.....0..0.0..0...........................

iii

Page

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16

22

23

LIST OF TABLES

Table
1. Reproductive and Developmental Characteristics of Some
Commonly Used Experimental Rodents ........................
2. Ingredients of Diets Used in Experiment I .................
. Ingredients of Diets Used in Experiment II ................
4. 'Weight Gain, Dry Protein Consumption, and PER for 4 Species
of Rodents at Different Levels of Casein ..................
5. 'Weight Gain, Dry Protein Consumption, and PER for 2 Species
of Rodents Using Different Proteins .......................
6. PERs for Frequently Used Bioassay Test Animals ............

iv

Page

10

12

14
19

LIST OF FIGURES

Figure

1. Average Protein Efficiency Ratio (PER) of 4 Species of
Rodents at Different Levels of Casein ....................

2. Average Protein Efficiency Ratio (PER) of 4 Species of
Rodents Using Different Proteins .........................

Page

13

15

PURPOSE

The object of this study was to determine certain nutritional
characteristics of two species of cotton rats, Sigmodon hispidus and
.§° fulviventer, and of the South American field mouse, Akgdgn_aggg§g, and
to compare these with comparable nutritional characteristics of the
meadow vole, Microtus pennsylvanicus. It is hoped that the null
hypothesis, Hb: The three species tested are not different from
QM.‘p§npsylvanicus or from each other in the characteristics studied, will

be disproved.

INTRODUCTION

Nutritionists have long been interested in determining food
qualities by measuring growth responses in selected organisms. As
bioassay test organisms, rodents have proven highly useful in studies of
various kinds. They take up little space and are easy and fairly
inexpensive to maintain. The gestation period of rodents is relatively
short, the litters are often large, and the young mature quickly.
Colonies can be built up rapidly and, if using wild rodents, can be
replenished with fresh stock as needed.

Voles of the genus Microtus CM. enn lvanicus, Elliott, 1963) have
proved excellent bioassay test mammals. These rodents are easily bred in
captivity and.weanlings respond in a highly sensitive manner to food
stuffs containing different levels of selected nutrients (Shenk‘gtuglr,
1970). Species of Microtus occur naturally in northern parts of North
America, Europe and Asia, but are rare and only'locally distributed in

remote mountain sectors of northern Latin America (Hall & Kelson, 1959).

To test some common NeotrOpical rodents for suitability as bioassay test
animals, cotton rats of the genus Sigmodon and South American field mice
of the genus Akgdgg_were studied. Cotton rats are common grassland
rodents ranging from central United States southward to Perd'(Baker,
1969) and the field mice are common in many parts of South America
(Cabrera, 1961). If selected animals representing these genera proved
successful in bioassay test trials, these Neotropical groups might prove
valuable to Latin American nutritionists desiring to establish breeding
colonies of locally adjusted and easilyhcaptured test animals. These
animals might also prove useful as laboratory stocks in related
biomedical investigations.

Table 1 compares gestation and maturation of the young for the two
genera studied here and 4 other commonly used experimental rodents.
Although the gestation period for Sigmodon is somewhat longer and the
litters smaller than the white rat,it can be weaned and reach breeding
age in about half the time of'Rattug, Akgggg_is somewhat comparable to
fiattu§.except sexual maturity is reached at an earlier age and litters
are not so large. Akgdgg is also much smaller than the white rat.

One chief drawaback in using wild rodent species rather than
domesticated strains of‘Mu§_or EEEEEE is they are much more excitable
and therefore more difficult to handle (Harris & Thimann, 1948). Unlike

Microtus, this wildness has not yet been successfully bred out of

Sigmodon in captivity.
Protein Evaluation Tests:

The three most commonly used protein evaluation tests according to

Sheffner (1967) are as follows:

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1. Protein Efficiency Ratio (PER) is used mainly in feeding
experiments with small animals and measured by gain in weight/'
protein intake. However, Block & Mitchell (1946) do not
believe that this is a true efficiency ratio because not all of
the protein is used for growth, but only that consumed above

maintenance.

2. Biological Value (BV) is determined by the nitrogen balance
and defined as nitrogen retained/nitrogen absorbed. It
measures the percent absorbed nitrogen retained for growth and
maintenance but does not include the correction needed for

maintenance to achieve the maximum efficiency of utilization.

3. Net Protein Utilization (NPU) expresses both digestibility
and BV. It is expressed by the coefficient of digestibility X

BV and represents the prOportion of nitrogen retained.

It was decided to use the PER method for several reasons: (1) It
is the simplest and most convenient method of'measuring nutritive value
of proteins; (2) PERs correlate highly with NPUs (Bender, 1956); and
(3) this was the method used by Shenk, Elliott, & Thomas (1970) in their
Microtus studies, with which this investigation is compared.

The efficiency with which protein is utilized is diminished if the
caloric intake is too low or if the protein is fed in excess. It is
usual to employ diets which provide more than the quantity of protein
needed for maintenance but less than that required for optimum.
performance (woodham, 1968). This accentuates the differences between

proteins thus making it easier to discriminate between samples.

EXPERIMENTAL
Test Mammals Used:

Rodents used in this study were descendants of individuals live-
trapped on MSU Museum field trips and maintained in laboratory colonies.

Sigmodon hispidus Say and 0rd. -- The wide-ranging hispid cotton rat
is distributed in grassy and brushy habitats from Nebraska to Peru.
Although it is adapted to a variety of hot, cool, moist and dry climates
at both high and low elevations, one sample was selected for study'from
13 km ENE of Pichucalco, elevation 61 m, in Chiapas, Mexico (180 N
latitude). Adults weigh, on the average, 110-115 grams. The parental
stock was captured in July 1969, in disturbed grassy areas between mixed
jungle and sugar cane fields. The annual rainfall at this locality is
heavy, approximately 3,500 mm.

Sigmodon fulviventer Allen. -- The tawnyhbellied cotton rat inhabits
the mesquite—grassland on the east side of the western Cordillera from
southern New Mexico and.Arizona south to the Mexican state of Michoacan.
Adults weigh, on the average, 175-200 grams. The parental stock was
captured in July 1968, 2 km,N of Gallego, elevation 1366 m, in Chihuahua,
Mexico (300 N latitude), on a shortgrass plain with a low annual rainfall,
approximately 150 mm.

Akgggg.§g§gag (Fischer). -— Azare's field mouse lives in grassy
habitats in southern South America (parts of Bolivia, Brazil, Uruguay,
and Argentina). Adults weigh, on the average, 19-21 grams. Parental
stock came from INTA, 20 km'w of Balcarce, elevation 100 m, Province of
Buenos Aires, Argentina, and was captured in June 1970. This grassland

locality receives approximately 860 mm of rainfall annually.

The test animals included, therefore, samples of Neotropical grass-
land rodents from a semi-arid temperate habitat (Sigmodon fulviventer),
from a moderatelyzhumid temperate habitat (Akodon azarae), and from a

humid, hot habitat (Sigmodon hispidus).
Methods:

Two separate experiments were run: (1) To determine what level of
casein is most efficiently‘utilized by the test animals; and (2) to
determine whether the test animals utilize Triticale, a wheat-rye cross,
as a protein source comparable to Microtus pgnngylvanicus (Elliott, 1963;
Shenk, Elliott, & Thomas, 1970). Conditions for each of the experiments
were simdlar with only the diets differing. Several sets of weanling
siblings were subjected to each of three diets in both experiments
conducted.

The diets in each experiment were isocaloric, with casein
(Hammerstein quality) being the chief variable and the amount of
carbohydrate, consisting of 2 parts cornstarch: 1 part dextrin: 1 part
sucrose, changing to compensate for the difference in calories. Two
experimental strains of triticale, MSU #358 (15.94% protein) and PC70
(15.25% protein), were then compared to the casein. Mazola corn oil,
Vitamin Diet Fortification Mixture, Salt Mix w, and Alphacel were then
added in specified quantities to supplement the diets.

Each diet was mechanically mixed and then pressed into wafers to fit
into spillproof feeders (Shenk & Elliott, 1969). These wafers were dried
in an oven at approximately65.5O C for 8-12 hours. They'were then left
in the experimental room.for 48-72 hours in order for the moisture

content to equilibrate relative to that of the air.

Animals in post-weaning stages gain the greatest amount of weight in
the shortest amount of time, so their sensitivity to small dietary
differences would be greatest. Also, in short term.assays with weanlings
emphasizing growth very little nutrient material is laid down as fat
reserves.

Test animals of the genus Sigmodon were weaned at 10-12 days, then
housed with siblings and fed Purina Mouse Breeder Chow for 2-3 days,
until they weighed at least 15 gms. After this short acclimation period,
they were fed the experimental diets for a test period of 10 days.
Occasionally older rats were used, but protein was utilized most
efficiently by the younger rats. Test animals of the genus Akgggn were
weaned at 12-14 days, fed Purina Mouse Breeder Chow for 2-3 days until
they reached a weight of at least 6-7 gms., and then fed the experimental
diets for 6-7 days.

Whitmoyer (1956) found there were significant differences in growth
rates of Microtus pennsylvanicus attributable to sex during the first 4
weeks. Although there is a slight difference in growth rates of‘male and
female Sigmodon hispidus, Jimenez (1969) found the difference was not
highly significant in young animals, and there is no significant
difference between sexes of.§. fulviventer. Peter Dalby (personal
communication) reports there are no significant differences in growth
rates between sexes in Akgggn. Therefore, both males and females were
used in this studyu

During each test, animals were individually housed in small
disposable plastic cages with metal tops. Ground corn cob was used for
bedding, a piece of cotton was used for nest material. 'Water and food

were offered ag.libitum. The tests were run in a room that housed a

colony'of meadow voles (Microtus) with a relatively constant temperature
of 15.60 c, 75—85% humidity, and with 24 hours of light per day.

weights of the animals and of the food were determined at the
beginning and at the end of the test periods. Per cent of dry weight of
the food was determined by standard oven drying at 100° c for 3 hours.
Protein Efficiency Ratios (PER) were determined by using the formula:

PER = weight gained by the animal .
amount of dry protein consumed

Experiment I: Determination of most efficiently utilized level of casein.

Siblings from each of 8 litters of weanling Sigmodon hispidus, from
each of 11 litters ofIS. fulviventer, and from each of 9 litters of
Akodon azarae were fed isocaloric diets containing 7% (Diet 1), 14%

(Diet 2), or 21% (Diet 3) casein, as shown in Table 2.
Experiment II: Comparison of qualities ofl3 proteins.

From Experiment I it was determined that test animals of all three
species utilized protein best at the 7% level, so all diets in
Experiment II contained 7% protein. Using the same techniques as above,
siblings from each of 16 litters of'S, his idus, from each of 15 litters
of _S_. fulviventer, and from each of 16 litters of A. M were fed
isocaloric diets that contained either casein (Diet 1), Triticale-MSU
#358 (Diet 2), or Triticale-Rockefeller PC70 (Diet 3) as shown in Table 3.
The PERs calculated from this test were then compared with findings of

known PERs of Microtus pennsylvanicus and other animals.

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RESULTS

Table 4 shows the average weight gain, amount of dry protein (casein
at levels of 7%, 14% and 21%) consumed, PER, and sample size (n) for each
of the three samples of the species studied, Sigmodon fulviventer, S,
his idus, and.Akgggpiggarag, and also includes values for Microtus
pennsylvanicus obtained by Dr. Fred Elliott and his associates at
Michigan State University in the last few years. Standard errors for
each value are also included. These results are compared in Figure 1.

Table 5 shows similar values found for each of the species in

Experiment II and the results are graphed in Figure 2.

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Figure 1. Average Protein Efficiency Ratio (PER) of
4 Species of Rodents at Different Levels of Casein.

o Sigmodon fulviventer

0 Sim. odon hispidus
A3.Akodon azare

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15

Figure 2. Average Protein Efficiency Ratio (PER) of
4 Species of Rodents Using Different Proteins.

O Sigmodon fulviventer
Q Sigr_nodon hispidus
A Akodon azarae

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1 l J
casein Triticale'MSU #358 Triticale Rockefeller PC70
PROTEIN (7%)

ANALYSIS OF DATA AND DISCUSSION

As the amount of protein in the diet is increased, both the weight
gain and the amount of dry protein consumed increase. However, as can
be seen in Table 3, the amount of protein consumed increases at a faster
rate than the weight gain, which accounts for the decreased efficiency of
utilization.

Table 3 and Figure 1 show that the most efficient use of casein
occurs at the 7% level for all 4 species of rodents. As the amount of
casein in the diet increases, the efficiency of utilization decreases.
This agrees with reports that there is a significant linear trend toward
reduced efficiency of utilization of digestible protein with increasing
levels of dietary protein (Greeley'gt_§l,, 1964). When intake exceeds
the requirement, efficiency of utilization must decrease rapidly since
protein cannot be stored in the body to any appreciable extent (Hegsted
& Chang, 1965).

Shenk‘gt.§l. (1970) report that maximum.casein efficiency values of
2.5 were obtained for‘M} pennsylvanicus between 5% and 8% casein in the
region of 8% to 23% fiber. Efficiency decreased below this point.
Therefore it was decided to not test Sigmodon and.Akgggn on diets
containing less than 7% casein at this time.

The PERs of the experimental species correlate quite well with those
of Microtus at the 7% and 14% levels. Microtus was not directly tested
at the 21% level, but the PERs of the other three species are quite
similar. Using the Student's t-test it was found that there is no
difference (P“<.05) between any'of the species except S, hispidus and
£52922: the highest and lowest values respectively, at 7% and 14% casein

levels.

16

17

There are no significant differences between PERs of M at the
different levels of protein, except between 7% and 21% casein, as was the
case in Microtus. It is interesting to note, however, that there is a
significant difference between the PERs of S. fulviventer at 7% and 14%
levels, but not at 14% and 21% levels, whereas there is no difference
between 7% and 14% levels of S. hispidus but there is between 14% and 21%
levels. This would seem to indicate that S. fulviventer is more
sensitive to lower levels of protein. A larger sample size should be
used to confirm this point. However, if indeed this is true, then, even
though the PERs for S. hispidus are somewhat higher and there is no
significant difference among these two species and Microtus, it would
appear that S. fulviventer might be more similar to Microtus, and S.
hispidus might actually be slightly more comparable to the albino rat.
The latter has been found to utilize 10% casein most efficiently (Chapman
e_t a_l., 1959). .It would be most interesting to conduct a study directly
comparing the white rat with these two species of cotton rats. S'godon
hispidus should also be tested at intermediate levels (between 7% and 14%)
of casein to find more accurately which level is most efficiently
utilized.

Since the 7% level of casein was found to be most efficiently
utilized, this diet was used in all feeding trials in Experiment II.
Using a two-way analysis of variance it was found that there was no
difference within each species in the qualities of the three proteins,
casein, Triticale-MSU #358, and Triticale-Rockefeller PC70. There was,
however, a difference among species. Using Student-Neumann-Keuls test
for Least Significant Range (ISR) (Sokal & Rohlf, 1969) it was found that

Akodon was significantly different (P) .05) from both species of cotton

18

rats in all 3 cases and was different from Microtus in all but the 7%
casein diet.

Several other animals besides those mentioned thus far have been used
for protein quality studies. Some of the most useful animals have been
chicks (Woodham, 1968; Miller & Kifer, 1970; Ousterhout & Snyder, 1962;
Blamberg, 1971), swine (Greeley e_t_ 32,, 1964; Pond e_t_ g” 1966), and
chinook salmon (Hastings, 1969). Protein Efficiency Ratios have been
determined for these and other animals, but quite often different
proteins are used. Procedures vary according to the species and the
researcher. Table 6 gives PER values for several animals with casein as
the test protein at specified percentages of protein and test periods of
particular lengths.

Both species of Siggodon fit in well with these PER.values. éggggg
is somewhat low, but no lower than one PER value that has been stated for
the albino rat (Block & Mitchell, 1946).

The white rat is chiefly a seed-eater as Opposed to Microtus and
Sigmodon (Baker, 1971) which seem to be mostly grass-eaters. Thus Sgifiug
feeds on high-caloric but hard-to-get food whereas the other 2 species
feed on lowhcaloric but easily obtained food (Verontsov, 1960). It would
seem reasonable, then, to suppose that grass-eaters should be able to
utilize efficiently a lower percentage of protein than seed-eaters since
there is a higher percentage of protein in seeds. Unfortunately, close
comparisons of'Sggggg'with Siggodon and.NHcrotus with respect to protein
utilization have not yet been made.

The ubiquitous S, hispidus appears to be more catholic in its feeding
habits than the restricted S, fulviventer. This might help explain why

the former is not quite as sensitive to lower protein diets as the latter.

19

Table 6. PERs for Frequently Used Bioassay Test Animals.

 

 

 

 

 

 

 

 

 

 

 

% Test
Test Animal Protein Period PER Reference
Chinook salmon 26. 5%* ..... 2.38 Hastings, 1969
Young swine 18% 2 wks. 4.8 Barnes e_t a_l,, 1966
Albino rats 10% 4.8 wks. 2.0 Block & Mitchell, 1906
2.5 Chapman _e_t _a_l_.,, 1959
2.7 Barnes fl _al., 1966
Albino mice 8.5% 7-8 days 2. 5 Bosshardt _e_t_ _a_l_., 19%
Microtus
pennsylvanicus 7% 6-10 days 2. 5 Shenk, Elliott & Thomas, 1970
Siggodon
hispidus 7% 10 days 3.1
S. gulviventer 7% 10 days 2.8
Akodon azare 7% 6 days 2.0

 

*Minimum protein level dependent on water temperature (Mertz, 1969).

20

Sigmodon hispidus should be better adapted to utilizing protein at a
wider range of concentrations. Sigmodon fulviventer, on the other hand,
occurs in semi-arid grassland plains where protein levels in forage are
generally constant and concentrated.

This difference found between the two species of cotton rats might
also depend on the difference in their genetic make-ups. The difference
in size alone could have some bearing on the efficiency of utilization of
the protein. However, there could also be sufficient genetic difference
between subspecies of either of the two species to cause a different
degree of efficiency. Drickamer & Bernstein (1972) found that there is
indeed a significant inverse relationship between latitude and weight
gain of two subspecies of Peromyscus maniculatus during the first two
weeks of life. Sigmodon fulviventer shows a decline in overall size from
north to south (Jimenez, 1969), but there might be some relation to size,
rate of development, and protein utilization.

It should be noted that these samples of cotton rats do not
necessarily represent the whole species with respect to growth, litter
size, and other characteristics. It would.be necessary to test several
different subspecies from each species (especially Sigmodon hispidus) A
from different areas to determine what the variations would be. This
information would be useful to both nutritionists and zoologists.

It appears, therefore, that Sigmodon would make a suitable animal
for bioassay of food stuffs. It behaves similar to Microtus
pgggsylvanicus in efficiency of utilization of protein.

Aggggg seems to respond somewhat differently, indicating that it
does not utilize the protein as well as the other species. This could

be due to the fact that it is a much smaller rodent, may'have a higher

21

rate of metabolism, needs more energy to maintain itself, and thus must
eat more food in order to gain a comparable amount of weight. Peter
Dalby (personal communication) reports that éggggg,has a low geometric
growth rate for the first few weeks of life compared to the Microtines,
which could be another reason why different results were found with this
rodent. Also, these animals were quite wild and were only a few
generations removed from the wild. A faw generations more in the lab
might have made a much more manageable group to work with and more
typical results might have been Obtained. Even though Akgggg.does have
somewhat lower PER values than either Siggpdon or Microtus, it responds
in a similar manner, and once a base PER is known for this species, it

might also make a suitable bioassay animal.

SUMMARY

The weanlings of three Neotropical rodents were evaluated to
determine their suitability as bioassay test mammals for nutrition
studies. The findings were compared with those for Microtus

nns lvanicus, which occurs in northern parts of North America. The
three species chosen were taken from strikingly different habitats:
(l) A semi-arid temperate habitat (Simodon fulviventer); (2) a
moderatelyhhumid temperate habitat (Akodon‘gggggg); and (3) a humid, hot
habitat (Siggodon hispidus).

Two exPeriments were run, using the same methods as Shenk, Elliott,
& Thomas (1970). Experiment I determined which level of protein (casein)
was most efficiently utilized by weanlings for growth. Three siblings
from each of several litters of each species were fed three different
isocaloric diets with various percentages of casein (7%, 14%, and 21%)
with only the amount of carbohydrate changing to make up the difference
in calories. Experiment II tested the qualities of Triticale-MSU #358,
and Triticale PC70 (wheat—rye hybrids) and 7% casein by comparing Protein

Efficiency Ratios (PER).
7 Very little difference in PERs was found.between casein and the
Triticale lines. However, PER values for Aggggg_were significantly lower
than those for the other three species. Possibly because of its small
size it has a higher rate of'metabolism and needs more protein for a
comparable weight gain.

It appears that, in comparison with Microtus pgnnsylvanicus, Siggodon
would make a suitable bioassay test organism for nutrition studies, and
although.§§gggg'is somewhat lower, it also follows the same pattern and
with the base PER.kn0wn, it might also make a useful bioassay mammal.

22

LITERATURE CITED

Anonymous
1961. Management of laboratory animals. In Manual for laboratory
Animal Care. Ralston Purina Co. 57 PP.

Baker, R. H.
1969. Cotton rats of the Si odon fulviventer group, p. 177-232.
In J. K. Jones (Ed.) Contributions in Mammalogy. Univ. of
Kansas Publ.

1971. Nutritional strategies of myomorph rodents in North.American
grasslands. J. Mamm., 52(4):800-805.

Barnes, R. H.,'W. G. Pond, E. Kwong and I. Reid.
1966. Effect of severe protein-calorie malnutrition in the baby
pig upon relative utilization of different dietary proteins.
J. Nutr., 89(3):355-364.

Bender, A. E.
1956. Relation between protein efficiency and net protein
utilization. Brit. J. Nutrition, 10:1351143.

Blamberg, D. L.
1971. A chick bioassay for evaluating the protein quality of dry
breakfast cereals. Poultry Sci., 50:300-302.

Block, R. J. and H. H. Mitchell
1946. The correlation of the amino-acid composition of proteins
with their nutritive value. Nutr. Abstr. Revs., 16:249.

Bosshardt, D. K., L. C. Ydse, M; M; Ayres, and R. H. Barnes
1946. The use of mice for the measurement of the growth promoting
quality of proteins. J. Nutr., 31:23-33.

Burt, W. H.
1969. Mammals of the Great Lakes Region. The Univ. of Mich. Press,
Ann Arbor, p. 124-126.

Cabrera, Angel
1961. Catalogo de los Mamiferos de America del Sur. Rev. Mus.
Argentino, Cienc. Nat. Zool. IV:508-509.

Chapman, D. G., Raul Castillo, and J. A. Campbell
1959. Evaluation of protein in foods. I. .A method for the
determination of protein efficiency ratios. Can. J. Biochem.

Physiol., 37:679-686.

23

24

Dalby, Peter
1972. Personal communication.

Drickamer, L. C. and Joan Bernstein
1972. Growth in two subspecies of Peromyscus maniculatus. J. Mamm.,
53(1):228-23l. ‘

Elliott, F. c.
1963. The meadow vole (Microtus pgnnsylvanicus) as a bioassay test
organism for individual forage plants. Quart. Bull. Mich.
Agr. Exp. Sta., 46:58-72.

Goertz, John W.
1965. Sex, age and weight variation in cotton rats. J. Mamm.,

Greeley, M. G., R. J. Meade and L. E. Hanson
1964. Energy and protein intakes by growing swine. I. Effects on
rate and efficiency of gain and on nutrient digestibility.
J. Anim. Sci., 23:808.

Hall, E. R. and K. R. Kelson
1959. The Mammals of North America. Ronald Press 00., New York,
2:viii + 547-1083 + 79 p.

Harris, R. S. and K. V. Thimann
1948. Vitamins and Hormones. Advances in Research and Applications.
6:xi + 435 p. Academic Press, Inc., New Yerk. Collection of
8 critical articles on vitamins and hormones, one being:
Nutritional requirements of the cotton rat and hamster, by
B. S. Schweigert.

Hastings, W. H.
1969. Fish in Research. 0. W. Neuhaus and J. E. Hulver (Ed.)
p. 263-292. Academic Press, New Yerk.

Hegsted, D. M. and Yet-0y Chang
1965. Protein utilization in rowing rats at different levels of
intake. J. Nutr., 87(1 :19-25.

Jimenez, Jorge V. J.
1969. Comparative postnatal growth in cotton rats (genus Siggodon).
Thesis for Degree of Ph.D. Mich. State Univ.

Mertz, Edwin T.
1969. Fish in Research. O.'W. Neuhaus and J. E. Hulver (Ed.)
p. 233-244u Academic Press, New'York.

Meyer, B. J. and R. K. Meyer
1944. Growth and reproduction of the cotton rat,_Si odon his idus,
:Eéflfiééfiflo'flhder.laberatory conditions.. J. Mamm.,25(2):107-129.

25

Miller, D. and R. R. Kifer
1970. Factors affecting protein evaluation of fish meal by chick
bioassay. Poultry Sci., 49:999-1004.

Ousterhout, L. E. and D. G. Snyder
1962. Nutritional evaluation of fish meals using four short-term
chick tests. Poultry Sci., 41:1753-1757.

Pond, W. G., R. H. Barnes e_t_ Q.
1966. Protein deficiency in baby pigs. p. 213-224. In L. K.
Busted and R. 0. McClellan (Ed.) Swine in Biomedical Research.
Pacific N. W. Lab., Richland, Wash.

Sheffner, A. L.
1967. Q1 vitro protein evaluation. p. 125-195. In Anthony A.
Albanese (Ed.) Newer Methods of Nutritional Biochemistry III.
Academic Press, New York.

Shenk, J. s. and F. 0. Elliott
1969. A diet feeder for weanling meadow voles (Microtus
pennsylvanicus). Lab. Anim. Care, 19:522-523.

Shenk, J. S., F. C. Elliott and J. W. Thomas
1970. Meadow vole nutrition studies with semisynthetic diets. J.
Nutr., 100:1437-1446.

Sokal, R. R. and F. J. Rohlf
1969. Biometry. The Principles and Practice of Statistics in
Biological Research. W. H. Freeman & Co., San Francisco,

776 pp.
SVihla’ A.
1929. Life history notes on Sigmodon hispidus hispidus. J. Mamm.,
10(4) =352-353 -

Vorontsov, N. N.
1960. The ways of food specialization and evolution of the alimentary
system in M'uroidea. International Sym. Theriologicum, Brno,
Acad. Scient. Bohemosloveniae, p. 155-158 (mimeograph in
English).

Whitmoyer, T. F.
1956. A laboratory study of growth rate in young Microtus
mnngylvanicus. Thesis for Degree of M.S., Mich. State Univ.

Woodham, A. A.
1968. A chick growth test for the evaluation of protein quality in
cereal based diets. I. Development of the method. Brit.
Poultry Sci., 9:53-63.

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