University of Nebraska - Lincoln
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Faculty Papers and Publications in Animal Science
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10-12-1988
EFFECT OF SEX RATIO OF THE BIRTH
LITTER ON SUBSEQUENT REPRODUCTIVE
PERFORMANCE OF GILTS
W. R. Lamberson
University of Missouri, Columbia
R. M. Blair
University of Missouri, Columbia
K. A. Rohde Parfet
University of Missouri, Columbia
B. N. Day
University of Missouri, Columbia
R. K. Johnson
University of Nebraska - Lincoln
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Lamberson, W. R.; Blair, R. M.; Rohde Parfet, K. A.; Day, B. N.; and Johnson, R. K., "EFFECT OF SEX RATIO OF THE BIRTH
LITTER ON SUBSEQUENT REPRODUCTIVE PERFORMANCE OF GILTS" (1988). Faculty Papers and Publications in Animal
Science. Paper 47.
http://digitalcommons.unl.edu/animalscifacpub/47
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EFFECT OF SEX RATIO OF THE BIRTH LITTER
ON SUBSEQUENT REPRODUCTIVE
PERFORMANCE OF GILTS 1
W. R. L a m b e r s o n 2 , R. M. Blair 2 , K. A. R o h d e Parfet 2 , B. N. Day 2 and R. K. J o h n s o n 3
University of Missouri 2 , C o l u m b i a 65211 and
University o f Nebraska 3 , Lincoln 68583
ABSTRACT
Records on age at puberty from 1,555 gilts and total number of pigs born in litters of 1,187
gilts from the Nebraska gene pool population were used to evaluate the effects of uterine environment on subsequent reproductive performance. Independent variables were line, year, line • year,
proportion of males in the birth litter (sex ratio), number born in the birth litter (fraternity size)
and sex ratio • fraternity size. Sex ratio, fraternity size and their interaction influenced age at
puberty (P < .01) but not number born (P > .2). Partial regression coefficients indicated that age
at puberty tended to decrease as sex ratio increased, particularly in small litters. Although the regression coefficients were relatively large, sex ratio, fraternity size and their interaction accounted
for only 1.3% of the variation in age at puberty within line • year subclass. These results offer
little encouragement for the use of sex ratio as a phenotypic selection criterion for improvement of
reproductive performance in giks. Results suggest that female swine are similar to rodents in
response to uterine environmental effects.
(Key Words: Pigs, Puberty, Litter Size, Prenatal Period, Siblings, Sex Ratio.)
Introduction
"Reproductive p e r f o r m a n c e
is o f great
i m p o r t a n c e in the efficiency o f swine product i o n (Tess et al., 1983). Heritabilities o f reproductive traits t e n d to be low to m o d e r a t e , .10
for litter size and .31 for age at first estrus
(Young et al., 1978). Low heritabilities suggest
t h a t factors other than additive genetic effects,
which m a y or may n o t be subject to control by
producers, a c c o u n t for substantial a m o u n t s o f
variation in these traits.
R e p r o d u c t i v e traits m a y be influenced by
the endocrine e n v i r o n m e n t to which gilts are
exposed in utero. It has been shown (vomSaal,
1981) that age at first estrus and length o f
reproductive lifetime of female rodents were
affected by their in u t e r o position with respect
to the sex of their adjacent littermates. F o r d et
al. (1980) r e p o r t e d that testes of the fetal pig
secrete testosterone during a period critical in
the differentiation o f internal and external genitalia. The p r o p o r t i o n of gilts exhibiting estrus
by 250 d o f age and weight o f reproductive
organs were significantly reduced in gilts b o r n
to females treated with testosterone p r o p i o n a t e
on d 30, 50 or 70 o f gestation (Elsaesser and
Parvizi, 1979).
The probability that a male fetus occupies a
specified position adjacent to a given fetus in
u t e r o is equal to the sex ratio o f the litter.
Thus, it is h y p o t h e s i z e d that gilts born in litters
with high sex ratios or a large p r o p o r t i o n o f
males have increased likelihood o f being exposed
to elevated concentrations of testosterone
prenatally c o m p a r e d with gilts born in litters
with low sex ratios. The objective o f this study
was to evaluate the effect of sex ratio o f birth
litter and its interaction with litter size on
reproductive traits in gilts.
1Contribution from the Missouri Agric. Exp. Sta.,
journal series no. 10354. This study was supported in
part by U.S. Dept. of Agric. grant no. 85-CRCR-11874.
2 Dept. of Anim. Sci.
3 Dept. of Anita. Sci.
Received July 16, 1987.
Accepted October 13, 1987.
Data used for this study were collected at
the University of Nebraska Field L a b o r a t o r y at
Mead, Nebraska. Genetic c o m p o s i t i o n o f the
gene pool p o p u l a t i o n was described by Cunningham and Z i m m e r m a n (1975). These data
were collected during 1979 to 1986 on f o u r
Materials and Methods
595
J. Anita. Sci. 1988. 66:595-598
596
LAMBERSON ET AL.
TABLE 1. DESCRIPTIVE STATISTICS FOR AGE AT PUBERTY AND NUMBER BORN
Trait
No.
.~
SD a
Age at puberty
Number born
Sex ratio b
Fraternity sizeb
Sex ratio c
Fraternity size c
1,555
1,187
601
601
540
540
169.6
9.5
.50
9.8
.49
9.9
26.4
2.9
.16
2.6
.15
2.8
aSD = standard deviation.
bLitters contributing gilts used in age at puberty analyses.
CLitters' contributing gilts used in analyses of number born.
lines o f swine involved in a n e x p e r i m e n t in
w h i c h s e l e c t i o n was applied to decrease age at
p u b e r t y in o n e line, t o increase litter size in o n e
line a n d at r a n d o m in t w o lines.
Pigs were m a i n t a i n e d in c o n f i n e m e n t . O n l y
gilts were f a r r o w e d . Piglets w e r e f o s t e r e d w i t h i n
line w i t h t h e i n t e n t i o n t h a t n o gilt rear m o r e
t h a n 10. W e a n i n g was at 28 d. Pigs were confined in t h e n u r s e r y in p e n s o f 25 u n t i l 56 d o f
age. F r o m 56 d to b r e e d i n g age, gilts were
h o u s e d in single-sex g r o u p s o f 10 in m o d i f i e d
o p e n - f r o n t buildings.
Traits s t u d i e d were n u m b e r b o r n (NB),
d e f i n e d as t h e n u m b e r o f fully f o r m e d piglets,
a n d age at first estrus (AP). E v a l u a t i o n o f AP
was b e g u n w h e n t h e oldest pig in a p e n was n o
older t h a n 135 d o f age. O n c e e a c h d a y gilts
w e r e m o v e d to a c o m m o n h e a t c h e c k p e n a n d
e x p o s e d to a m a t u r e i n t a c t b o a r f o r 20 m i n . A
gilt was c o n s i d e r e d to be in estrus if she s t o o d
solidly t o a m o u n t b y t h e boar. Estrus d e t e c t i o n was c o n t i n u e d u n t i l all gilts were f o u n d in
estrus o r t h e y o u n g e s t gilt n o t f o u n d in estrus
was 2 5 0 d o f age. No m o r e t h a n 3% o f gilts in
a n y y e a r failed to express estrus. R e c o r d s f r o m
gilts t h a t failed to express e s t r u s were e x c l u d e d
f r o m t h e analysis. G e n e r a t i o n interval was 1 yr.
F a r r o w i n g o c c u r r e d d u r i n g late w i n t e r each
year.
D a t a were a n a l y z e d using o r d i n a r y l e a s t squares analysis o f variance. A m o d e l i n c l u d i n g
t h e discrete effects o f line, year, t h e i n t e r a c t i o n
o f line x year a n d t h e c o n t i n u o u s effects o f
f r a t e r n i t y size ( F R A T ) , d e f i n e d as t h e n u m b e r
o f pigs in t h e gilts' b i r t h litter, sex r a t i o (SR),
d e f i n e d as t h e p r o p o r t i o n o f t h e gilts' b i r t h
l i t t e r t h a t was male, a n d t h e i n t e r a c t i o n bet w e e n F R A T a n d SR was f i t t e d t o e a c h d e p e n -
TABLE 2. A N A L Y S E S O F VARIANCE FOR AGE AT PUBERTY AND NUMBER BORN
:.,
,,.
Age at puberty
Source of variance
df a
Mean
square
Line
Year
Line • year
Fraternity size
Sex ratio
Fraternity size • sex ratio
Error
3
6
7
1
1
1
1,535
10,400" *
4,337**
1,609"
4,383 **
4,281"*
3,886*
621
adf = degrees of freedom.
*P<.05.
**P<.01.
Number born
df
3
5
13
1
1
1
1,162
Mean
square
142.5"*
32.4*
15.6
.2
2.8
.05
7.3
EFFECT OF SEX RATIO ON REPRODUCTION OF GILTS
dent variable. Sire effects were not included in
the model because the potential application of
results from this study should be in selection of
replacement grits applied within contemporary
groups but across sire groups.
Results and Discussion
597
TABLE 3. PREDICTED AGES AT PUBERTY FOR
COMBINATIONS OF BIRTH LITTER
FRATERNITY SIZES AND
SEX RATIOS
Sex ratio
Fraternity size
.3
.5
.7
Age at puberty was measured on a total of
7
189
177
166
1,555 gilts. Descriptive statistics for the trait 10
180
171
162
are presented in Table 1. Results of the analysis 13
170
164
158
of AP are presented in Table 2. Each independent variable represented a highly significant
source of variation. Partial regression coefficients for the effects of FRAT, SR and their
interaction were - 2 . 2 + .8 d/pig in the birth
litter, --43.1 + 16.4 d/unit, and 4.2 + 1.7 d/pig reported by Edgerton and Cromwell (1986). In
x unit, respectively. Expressed as standard par- that study, low SR sows had larger litters than
rials, regression coefficients were .43 + .15 for high SR sows (10.2 vs 9.2; P < .05); however,
FRAT, .48 +- .19 for SR and .61 + .25 for their data from only six pairs of non-littermate sib
interaction. Predicted AP for nine combinations sows were used.
of FRAT and SR are presented in Table 3. AlStudies with rodents, reviewed by vomSaal
though the effects of SR, FRAT and their inter- (1981) did not reveal intrauterine position
action were highly significant, they together effects on NB. Effects on number surviving
accounted for only 1.3% of the variation in AP were dependent on the environment in which
after variation due to line, year and line • year the litter was reared. In an environment in
was removed, with each effect contributing to which there was competition among litters,
an approximately equal extent.
females exposed to male sibs in utero expressed
As the proportion of males increased in an advantage in number weaned.
litters, AP declined. The magnitude of decline
Sex ratio of the birth litter significantly
was greater in small litters. These results seem affected AP but not NB. Despite significant
contrary to expectations based on studies by effects of SR on AP and a relatively large
Elsaesser and Parvizi ( 1 9 7 9 ) In that study the regression coefficient, the low coefficient of
proportion of gilts attaining puberty by 250 d determination offers little encouragement for
of age was significantly reduced compared with SR to be used as a criterion in the selection of
controls (8.3 vs 45.5%) if their dams had been replacement grits. Results from this study
exposed to testosterone propionate between d suggest that female swine may be similar to
30 and 70 of gestation. In a study using mice, rodents in their response to uterine environvomSaal and Bronson (1978) categorized mental effects.
females as developing in utero between two
Literature Cited
females (OM) or between two males (2M).
When these females were individually placed in Edgerton, L. A. and G. L. Cromwell. 1986. Sex of
siblings may influence reproductive performance
cages next to a male, 2M females were older at
of sows. J. Anim. Sei. 63 (Suppl. 1): 365.
puberty than OM females. However, when females were grouped in cages next to a male, Elsaesser, F. and N. Parvizi. 1979. Estrogen feedback
in the pig: Sexual differentiation and the effect
2M females were younger at puberty than OM
of prenatal testosterone treatment. Biol. Reprod.
females. The latter situation may be more
20:1187.
similar to the present study because grits were Ford, J. J., R. K. Christenson and R. R. Maurer. 1980.
Serum testosterone concentrations in embryonic
housed in single-sex groups after d 56.
and fetal pigs during sexual differentiation. Biol.
Descriptive statistics for NB are presented in
Reprod. 23:583.
Table 1. Partial regressions of NB on FRAT, SR Tess, M. W., G. L. Bennett and G. E. Dickerson. 1983.
and their interaction were .04 -+ .10 pig/pig in
Simulation of genetic changes in life cycle efficiency of pork production. 2. Effects of compothe birth litter, .03 + 1.8 pig~unit, and .01 + .18
nents on efficiency. J. Anim. Sci. 56:354.
pig/pig • unit, respectively. None of these revomSaal, F. 1981. Variation in phenotype due to
gression coefficients approached statistical
random intrauterine positioning of male and
significance. These results are contrary to those
female fetuses in rodents. J. Reprod. Fertil.
598
LAMBERSON ET AL.
62:633.
vomSaal, F. S., and F. H. Bronson. 1978. In utero
proximity of female mouse fetuses to males:
Effect on reproductive performance during later
life. Biol. Reprod. 19:842.
Young, L. G., R. A. Pumfrey, P. J. Cunningham and
D. R. Zimmerman. 1978. Heritabilities and
genetic and phenotypic correlations for prebreeding traits, reproductive traits and principal
components. J. Anim. Sci. 46:937.
Zimmerman, D. R. and P. J. Cunningham. 1975.
Selection for ovulation rate in swine: Population,
procedures and ovulation response. J. Anim. Sci.
40:61.