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At least 19 recordsLinked to original sources
PubMed1990

A study on primiparous sows of the ability to show standing oestrus and to ovulate after weaning. Influences of loss of body weight and backfat during lactation and of litter size, litter weight gain and season.

The ability to show standing oestrus and to ovulate within 10 days of weaning was studied in 240 purebred Swedish Yorkshire primiparous sows, fed according to a conventional feeding regime during lactation. The sows were weighted and backfat depth was recorded at farrowing and at weaning. Oestrus control was performed daily and blood samples for determination of plasma progesterone were drawn regularly in 205 sows. The distribution among the sows of the first standing oestrus after weaning had 2 peaks. The first peak occurred within 10 days of weaning and the second 24-30 days after weaning. Twelve per cent of the sows ovulated without showing standing oestrus within 10 days of weaning and 4% had an anovulatory first oestrus within the same time. Significant differences in age at farrowing and in loss of weight and backfat during lactation were found between sows which both showed standing oestrus and ovulated within 10 days of weaning and sows which neither showed standing oestrus, nor ovulated within the same time. The season during which weaning occurred significantly influenced the ability to show standing oestrus and ovulate within 10 days of weaning. Among the sows which both showed standing oestrus and ovulated within 10 days of weaning, significant positive correlations were found between weight loss, litter size, litter weight gain and the interval from weaning to first standing oestrus.

Adipose Tissue↗
PubMed1992

Morphometric studies in inbred and hybrid house mice. VIII. Effects of litter size on brain size and body size.

Litter size, brain size, and body size were examined in inbred and hybrid house mice of three different ages in order to test whether litter size exhibits a positive genetic, but negative environmental association with both brain and body size. As estimated from among-line covariation, litter size showed a positive, but non-significant genetical association with brain and body size. It also showed a significant, negative environmental association with brain and body size, as hypothesized. Over all inbreds and hybrids, litter size explained 8% and 14%, respectively, of the within-strain (environmental) variation in brain and body size. It was concluded that the negative phenotypic association of litter size with brain size and especially body size is the reflection of a well-known negative maternal environmental effect whereby mice with large body sizes tend to produce larger litters of mice with smaller body sizes.

Animals↗
PubMed1985

Somatic and germ cell chimerism in chimeric mice between strains of high litter size and regular litter size.

CFO is an inbred strain of mice showing a high litter size. The high fertility of CFO is due mainly to a very low embryonic death rate during uterine development. C57BL and 129 strains are characterized by regular litter size. Crosses were made and CFO----C57BL and CFO----129 chimeras were produced. In CFO----C57BL mice, coat color of the C57BL predominated over that of CFO; internal chimerism except for that of the gonads was observed to be in the same proportion as the two genotypes, but the genotypic component of the gonads was almost entirely CFO. Germ cells undergoing gametogenesis in the CFO----C57BL mice were almost all derived from the CFO genotype, and the chimeric females showed high fertility just as did the CFO females. In the CFO----129 mice no obvious skewing toward one genotype was observed in the coat color, but the germ cells undergoing oogenesis in the two types of chimeric females were recognizable as nearly all of the 129 genotype but with the females showing the same high fertility as do the CFO females. This fact suggests that the genotypes of germ cells in the ovary or in developing embryos do not influence fertility, but rather that the litter size is controlled mainly by the uterine environment.

Animals↗
PubMed1994

Serum cholesterol concentration of mice selected for litter size and its relationship to litter size and testis mass.

This study assessed the genetic relationship between litter size and serum cholesterol concentration and between litter size and testis mass in mice. Mice were from a long-term experiment in which selection had occurred for 21 generations in three replicated lines per criterion of selection (LS = selection to increase litter size based on number born; LC = unselected control). Thereafter, random mating within lines was practiced. Serum cholesterol concentrations were evaluated in female and male mice from two replicates at Generation 29 and one replicate at Generation 30. Body weights and blood samples were collected from primiparous females 8 d after weaning their pups. Data from males were collected as they came out of breeding cages. In addition, the testes were excised, stripped clean of connective tissue and the epididymides, and weighed. Means for body mass of females and males, serum cholesterol, number born, and testis mass were as follows: 35.2 vs 32.5 g (P < .09), 33.9 vs 30.7 g (P < .08), 117.5 vs 110.5 mg/dL (P < .08), 14.0 vs 10.3 pups (P < .04), and 126 vs 122 mg, respectively, for LS and LC. Serum cholesterol was greater in males than in females (133.3 vs 95.1 mg/dL; P < .001), but there was no interaction between sex and selection criterion. Serum cholesterol concentration was not correlated phenotypically to number born or body mass, but it had a small negative relationship with testis mass. Therefore, we concluded that selection for litter size tended to increase serum cholesterol in addition to the increase in number born but did not change testis mass.

Animals↗
PubMed1984

Influence of reduced litter size and daily litter separation on fertility of sows at 2 to 5 weeks postpartum.

Two experiments were conducted to determine the influence of various lactational treatments on the incidence of estrus and subsequent fertility of sows. Experiment 1 consisted of 60 crossbred (Yorkshire X Duroc) sows assigned to one of four treatment groups. Litter size was reduced (RLS) to two to four nursing pigs/sow at 2 (n = 16), 3 (n = 15) or 4 (n = 15) wk of lactation for 5 d before final weaning or litters were weaned from control sows (n = 14) at 5 wk of age. Reduced litter size resulted in 19 of 43 (44%) sows detected in estrus on the day of weaning. More (P less than .05) RLS sows were in estrus 0 to 3 d after weaning than control sows. Fertility traits (number of corpora lutea, eggs recovered, egg recovery rate, eggs fertilized, fertilization rate, cleaved eggs and cleavage rate) were similar among treatment groups at 4 to 6 d postestrus. Experiment 2 consisted of 59 crossbred (Yorkshire X Duroc) sows assigned to one of four treatment groups. Litters were separated from their dams for 6 (n = 20) or 12 (n = 10) h/d between 2 and 4 wk or litters were weaned at 2 (n = 13) and 4 (n = 15) wk of age. Lactational estrus was detected in 13 of 20 (65%) sows and 5 of 10 (50%) sows that were separated from their litters for 6 or 12 h/d, respectively. Lactational estrus (LE, n = 18) in sows was observed 4 to 8 d after initial separation, while sows remaining anestrus during lactation (LA, n = 12) were in estrus 2 to 7 d postweaning. Average intervals from separation or weaning to estrus for LE and LA sows and for sows whose litters were weaned at 2 or 4 wk were 5.9, 4.4, 4.4 and 4.2 d, respectively, and were longer (P less than .05) for LE sows. Fertility traits were similar among treatment groups. These studies demonstrate that lactations of 2 to 5 wk and lactational treatments of sows, including either litter reduction before weaning or daily separation of sows from their litters, resulted in similar postweaning or post-treatment intervals to estrus and similar fecundity regardless of treatment or lactation length. While 50% of the sows responded to treatments, reasons for the lack of response in the remaining sows is not explained, but it appears that body weight and backfat of sows at weaning, and feed intake during lactation were unrelated to the success of the treatments imposed.

Animals↗
PubMed1986

Fertility, embryo survival and litter size in lines of Targhee sheep selected for weaning weight or litter size.

Conception rate, prenatal survival and litter size were recorded for 444 ewes of two age groups from five lines of grade Targhee sheep: two unselected control lines, HC1 and DC(C); two lines selected for 20 yr for increased 120-d weight, HW and DH(W); and a line selected for 18 yr for increased multiple births, T. Line T was equal or superior to the control lines in conception rate, prenatal survival and litter size in both age groups, although most of the differences were not significant. The W selected lines were inferior to the C and T lines in fertility and tended to be lower in prenatal survival, among mature ewes, resulting in a significantly lower number of lambs born per corpus luteum in the W lines than in the other two groups. Among yearlings, C ewes were non-significantly lower in fertility than T and W ewes, while W ewes were significantly lower than C and T ewes in prenatal survival. The T line ewes had higher overall reproductive performance than either of the other two groups. Ewes with two ovulations had a significantly higher conception rate than ewes with single ovulations. Gestation period was exceptionally uniform with a coefficient of variation of 1.3% and little difference due either to line or litter size. It was concluded that selection for multiple births improved overall reproductive performance, whereas selection for increased growth rate had an adverse effect on several components of reproduction, leading to a net decline in fitness.

Animals↗
PubMed1992

High and low litter size trait and its relationship with serum and urine progesterone, serum zinc, and serum phosphorus in New Zealand white rabbits and improvement for the low litter size trait.

A number of does was classified according to their initial litter size to high (> 6 bunnies, group 1) and low (< 5 bunnies, group 2) in New Zealand White rabbits. Incidence of low litter size in the herd in the present study was 23%. The number of matings/conception, total mortality, corpora lutea/foetus, number and percentage of resorbed foeti were markedly higher in group 2 than in group 1. The litter weight, number of foetuses, implantation sites, and corpora lutea in group 2 showed a marked decrease over group 1. Serum and urine progesterone levels in pregnant rabbits of group 2 were significantly (P < 0.01) lower than in group 1, however, non-efficacious progesterone levels were significantly (P < 0.01) lower in group 2. The zinc content in serum, foetal dry weight and uterine horn dry weight, and serum inorganic phosphate in group 2 were significantly (P > 0.01) lower than in group 1. The litter size was significantly (P < 0.01) correlated with zinc and inorganic phosphate in group 2, while it was correlated with serum and urine progesterone in the two groups. The correlation coefficients were significant (P < 0.01) between urine progesterone and serum zinc and between serum progesterone and inorganic phosphate more frequently in group 2 during the gestation period than in group 1. The treatment of group 2 does with calcium carbonate, sodium phosphate dibasic, and zinc acetate in drinking water improved the serum progesterone, urine progesterone, and non-efficacious progesterone in addition to serum zinc and inorganic phosphate, which led to improvement of the number of matings/conception, litter size and litter weight, and lowered total mortality.

Animals↗
PubMed1995

Differences in pup birth weight, pup variability within litters, and dam weight of mice selected for alternative criteria to increase litter size.

Selection for litter size had been practiced for 21 generations and relaxed selection for 13 generations in mice. Three replicates were used with four selection criteria: index of components (ovulation rate and ova success), uterine capacity, litter size, and an unselected control. Especially with selection for litter size and the index relative to the control, number of pups born had increased, and differences also occurred in mating weight. Dams of the three replicates and their litters were used to evaluate the effects of accumulated selection on pup birth weight, variability in weight of littermates, and dam's weight at mating and after littering. Total number born, number born alive, number of males, and number of females were also recorded and studied. Mean pup birth weight did not differ among the criteria; however, variability among littermates in pup weight tended to differ among criteria of selection. Regressions for pup weight and within-litter standard deviation of pup weight on number born were small and negative but significant (P < .001). The distribution of pup weight within litter was normal for 77.2% of the litters, with no differences among the criteria. The difference between weight of male and weight of female pups was significant (P < .001); overall males were 2.5% heavier than females. There was a difference (P < .02) among criteria in mating weight and littering weight; however, the maternal weight gain between mating and littering was not different among criteria. Number born differed (P < .003) among the criteria, but there was no significant difference among criteria in numbers of males and females.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1979

Effect of age and parity on litter size in pigs.

Litter size increased (P less than 0.01) as the age of the dam at farrowing increased. However, previous reproductive experience (parity) had no direct effect on litter size of dams of the same age.

Animals↗
PubMed1980

Ovulation rate, embryo survival and ovarian sensitivity to gonadotrophins in mice selected for litter size and body weight.

Single trait selection of mice for either large body size or large litter size resulted in an increased ovulation rate because of possible enhanced ovarian sensitivity to gonadotrophins. There was no difference in pre-implantation embryonic survival in either of the selected lines when compared to control mice. Selection for body weight did not alter post-implantation embryo survival, but fewer fetuses were lost after implantation in the litter size line compared to the control line. Index selection for large body size and small litter size did not change ovulation rate but increased pre- and post-implantation embryonic mortality. Selection for small body size and large litter size increased ovulation rate and decreased early embryonic death.

Animals↗
PubMed1989

Integration of ovulation rate, potential embryonic viability and uterine capacity into a model of litter size in swine.

A mathematical model of litter size in swine was developed from ovulation rate, potential embryonic viability and uterine capacity. The model assumed that ovulation rate was reduced to potentially viable embryos by factors innate to the ovum and embryo. Potentially viable embryos then could be further reduced to uterine capacity, the maximum number of fetuses that a female can carry to term. Consequently, litter size can be no greater than either ovulation rate or uterine capacity. Means and variances of ovulation rate and potential embryonic viability used in the model were based on experimental results. The mean and variance of uterine capacity were varied until the simulated mean and variance of litter size were equal to experimental results. Simulated results of relationships among ovulation rate, embryo survival and litter size were similar to observed experimental relationships. Heritabilities of simulated litter size and embryo survival were similar to literature values when the heritability of ovulation rate was set at .25 and the heritability of uterine capacity was set at either .15 or .20. Litter size was simulated for 25 combinations of average ovulation rate and uterine capacity to develop equations relating mean ovulation rate and uterine capacity to litter size, embryo survival and correlations among them. Results suggest that changing either ovulation rate or uterine capacity independently will not result in large changes in litter size. Consequently, the model suggests that a single gene, hormonal manipulation or nutritional change will not result in large increases in litter size and that combinations of factors will be needed to increase litter size.

Algorithms↗
PubMed1990

Availability of solid feed and growth rates of pre-weaned mice of different litter size.

The effects of litter size and availability of solid feed before weaning on the growth mice were studied. Pups of small litters (n = 3) grew significantly faster than mice of large litters (n = 10), the mean difference at weaning being about 3 g. The difference in body mass persisted after weaning; at the age of 98 d the mean difference was about 5 g. Availability of solid feed to pre-weaned mice significantly stimulated mass gain of litters consisting of 10 but not of 3 pups. Body masses of the dams during the suckling period were markedly influenced by litter size: Mice with 10 pups had increased body masses when compared with mice having 3 young. By the time of weaning, body masses of mothers with larger or small litters had become similar again just as they were immediately after parturition.

Animal Feed↗