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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↗
PubMed2006

Genetic parameters for canalisation analysis of litter size and litter weight traits at birth in mice.

The aim of this research was to explore the genetic parameters associated with environmental variability for litter size (LS), litter weight (LW) and mean individual birth weight (IW) in mice before canalisation. The analyses were conducted on an experimental mice population designed to reduce environmental variability for LS. The analysed database included 1,976 records for LW and IW and 4,129 records for LS. The total number of individuals included in the analysed pedigree was 3,997. Heritabilities estimated for the traits under an initial exploratory approach varied from 0.099 to 0.101 for LS, from 0.112 to 0.148 for LW and from 0.028 to 0.033 for IW. The means of the posterior distribution of the heritability under a Bayesian approach were the following: 0.10 (LS), 0.13 (LW) and 0.03 (IW). In general, the heritabilities estimated under the initial exploratory approach for the environmental variability of the analysed traits were low. Genetic correlations estimated between the trait and its variability reached values of -0.929 (LS), -0.815 (LW) and 0.969 (IW). The results presented here for the first time in mice may suggest a genetic basis for variability of the evaluated traits, thus opening the possibility to be implemented in selection schemes.

Analysis of Variance↗
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↗
PubMed2002

Multivariate analysis of litter size for multiple parities with production traits in pigs: II. Response to selection for litter size and correlated response to production traits.

Litter size and production trait responses to experimental selection for increased litter size in a Landrace pig population are reported. The numbers of sows and litters available for the first cycle of selection were 3,034 and 961, respectively. Selection was carried out using a BLUP repeatability animal model for number of piglets born alive (NBA). The experiment included one selection and one control line, each with three nonoverlapping generations. The selection line (H) consisted of the 160 sows with the highest breeding values and one boar from each of 25 full-sib families with the highest breeding values. The control line (C) consisted of 160 sows and 25 boars randomly chosen. The two subsequent generations in each line were obtained by random selection. A Bayesian analysis of genetic response using a multivariate model was carried out by Gibbs sampler. Marginal posterior distributions were obtained for direct response in NBA, and for correlated response in weight (WT), and backfat thickness (BT) at 175 d of age. The posterior means and posterior standard deviation (PSD) for direct genetic response of NBA ranged from 0.32 (PSD 0.08) in the first parity to 0.64 (PSD 0.08) in the fourth. The posterior means for correlated genetic response in WT and BT were -0.66 kg (PSD 0.36) and 0.20 mm (PSD 0.10), respectively. For WT and BT, the 95% highest posterior density regions (HPD) contain zero-correlated genetic response. Marginal posterior distributions of selection differentials were investigated. The posterior means for standardized selection differentials for NBA in different parities ranged from 0.70 (PSD 0.12) to 0.94 (PSD 0.06) in females for line H, from 0.22 (PSD 0.19) to 0.34 (PSD 0.10) in males for line H, and from 0.08 (PSD 0.08) to 0.13 (PSD 0.07) in females for line C. All available males were used in line C. Results from this experiment showed that selection for increased litter size is effective. Responses to selection were heterogeneous across parities, suggesting that litter size in each parity may have a different genetic background. No correlated genetic response to growth and backfat thickness was observed.

Adipose Tissue↗
PubMed2006

Analysis of litter size and days to lambing in the Ripollesa ewe. II. Estimation of variance components and response to phenotypic selection on litter size.

A performance data set from 376 Ripollesa purebred ewes of the experimental flock of the Universitat Autònoma of Barcelona was analyzed using a bivariate Bayesian threshold-linear model. The data set contained 1,598 litter size records and 1,699 days-to-lambing records. The model included the additive genetic effect of each animal and 3 nongenetic sources of variation: ewe age, year of lambing, and the permanent environmental effect characterized by the ewe. The flock was phenotypically selected for litter size since 1986, and replacement ewes and rams were selected from the progeny of the more prolific ewes, which had at least 3 deliveries recorded. The phenotypic trend for litter size was positive, whereas days to lambing followed an unclear pattern. Both traits had low heritabilities; 0.13 for litter size and 0.11 for days to lambing. Response to selection was evaluated through (a) the average breeding value of the ewe lambs chosen annually, and (b) the average breeding value of the overall flock. The first measurement suggested a positive trend for litter size, although it showed important oscillations. On the other hand, the average breeding value for the overall flock showed a stable positive tendency after yr 4 of selection, with estimates clearly different from zero after yr 11 of selection. A significant increase in the incidence of multiple births was observed, with a mode of approximately 10%. The correlated response in days to lambing did not show a significant trend. The effect of year of lambing also positively influenced both litter size and days to lambing, although important oscillations were observed between years. Results indicated that litter size in sheep can be effectively improved through phenotypic selection, even in small flocks; moreover, days to lambing could also be genetically improved, given the estimate obtained for its heritability.

Animals↗
PubMed2004

Epistasis affecting litter size in mice.

Litter size is an important reproductive trait as it makes a major contribution to fitness. Generally, traits closely related to fitness show low heritability perhaps because of the corrosive effects of directional natural selection on the additive genetic variance. Nonetheless, low heritability does not imply, necessarily, a complete absence of genetic variation because genetic interactions (epistasis and dominance) contribute to variation in traits displaying strong heterosis in crosses, such as litter size. In our study, we investigated the genetic architecture of litter size in 166 females from an F2 intercross of the SM/J and LG/J inbred mouse strains. Litter size had a low heritability (h2 = 12%) and a low repeatability (r = 33%). Using interval-mapping methods, we located two quantitative trait loci (QTL) affecting litter size at locations D7Mit21 + 0 cM and D12Mit6 + 8 cM, on chromosomes 7 and 12 respectively. These QTL accounted for 12.6% of the variance in litter size. In a two-way genome-wide epistasis scan we found eight QTL interacting epistatically involving chromosomes 2, 4, 5, 11, 14, 15 and 18. Taken together, the QTL and their interactions explain nearly 49% (39.5% adjusted multiple r2) of the phenotypic variation for litter size in this cross, an increase of 36% over the direct effects of the QTL. This indicates the importance of epistasis as a component of the genetic architecture of litter size and fitness in our intercross population.

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↗
PubMed2002

[Study of molecular genetics of the size of reproductive organs and litter size in the sow].

The mutations of ESR, PRLR and FSHR genes were investigated by SNP; 103 F2 sows were slaughtered and their reproductive organs were determined; the litter size of sow was recorded. The linkage between mutations of genes and size of reproductive organ, litter size was analyzed. The results revealed: these sows that could provide more piglets with bigger reproductive organs usually carried genotype like as genotype BB on the sites of ESR, FSHRB and the genotype AA on the sites of ESRB and PRLR, that is, the genotype of BB on the sites of ESR or FSHRB in sow was not only helpful to promote growth of reproductive organs, but also benefit to improve litter size; The size of productive organs and litter size of the sow with genotype AA on the sites of ESRB or PRLR were significantly higher than those of sow with genotype AB or BB.

Animals↗