Lifetime parental productivity in twenty-seven crosses of mice. I. Birth traits

Twenty-seven crosses derived from three random-mating, unselected strains of mice (SWO, J, PGH) with 16 matings/pureline or cross were cohabited continuously and monogamously for 365 d to evaluate long-term reproductive performance of the parents. Data from 3,249 litters born were analyzed to study the effects of parity (number of litters) and type of cross (pureline, two-way, backcross, three-way) on the following traits: 1) continuity of reproduction (COR), 2) litter size at birth (LSB), 3) age at first litter (AFL), 4) fraction alive at birth-the ratio of number born alive to LSB (FAB), 5) birth to birth interval (BBI) and 6) reproductive rate-the ratio of number born alive to birth to birth interval (RRT). Reproductive rate was also studied in a cumulative manner rather than on a per parity basis by regressing cumulative number born alive on cumulative birth to birth interval. Parity effects were important (P less than .01) for all traits measured. Differences among cross-types were highly significant for COR, LSB and RRT. Three-way crosses were more productive than backcrosses, and both were superior to two-way and pureline matings. Uniformity was greater among three-way crosses for all traits except COR. Cross-types differed importantly in the pattern of change in performance over parities for COR, LSB, FAB, RRT and cumulative number of live young (P less than .01). Number of parities were most important for variation in longevity of reproduction (COR) and somewhat for litter size (LSB). Mean and cumulative reproductive rates were influenced more by longevity and litter size than by interval between births.     

Genetic parameters for ewe productivity traits in the Columbia, Suffolk and Targhee breeds

Estimates of repeatability and heritability were obtained for the following productivity traits of ewes: litter weight at birth (LWB) and weaning (LWW), litter size at birth (LSB), litter size alive at birth (NBA), litter size at weaning (LSW), neonatal survival rate (SRB) and preweaning survival rate (SRW). Phenotypic and genetic correlations were estimated for litter traits. The data set contained 6,394 ewe breeding records from three state stations over 10 yr on 1,731 ewes that were the progeny of 488 sires among three breeds (Columbia, Suffolk and Targhee). Pooled intra-station estimates of repeatability ranged from .11 to .22 for LWB and LWW among the three breeds. For litter size at birth, number born alive and litter size at weaning these estimates varied from .09 to .17 and for the survival traits (SRB and SRW) the variation was from .11 to .20. Intra-station estimates of heritability for the three breeds varied from .12 to .28 for LWB and LWW, and for LSB, NBA and LSW estimates varied from .05 to .35. Heritability estimates for survival traits (SRB and SRW) were low, ranging from .00 to .14. Phenotypic correlations among LWB, LWW, NBA and LSW ranged from .35 to .92 among the breed-station subclasses, with higher correlations occurring where a part-whole relationship existed. The study suggests that selection of ewes with high litter size at birth or at weaning and(or) litter weight at birth or at weaning will genetically improve total litter weight at weaning per ewe lambing.     

Genetic relationship of litter traits between farrowing and weaning in Landrace and Large White pigs

We estimated genetic parameters in Landrace and Large White pig populations for litter traits at farrowing (total number born, number born alive, number stillborn, total litter weight at birth (LWB), and mean litter weight at birth) and those at weaning (litter size at weaning (LSW), total litter weight at weaning (LWW), mean litter weight at weaning (MWW), and survival rate from farrowing to weaning). We analyzed 65,579 records at farrowing and 6,306 at weaning for Landrace, and 52,557 and 5,360, respectively, for Large White. Single‐trait and two‐trait repeatability animal models were exploited to estimate heritability and genetic correlation respectively. Heritability estimates of LSW were 0.09 for Landrace and 0.08 for Large White. Genetic correlations of LSW with MWW were –0.43 for Landrace and –0.24 for Large White. Genetic correlations of LSW with LWW and LWB ranged from 0.5 to 0.6. The genetic correlation of MWW with LWW was positive, but that with LWB was negligible. The results indicate that utilizing LWW or LWB could improve LSW efficiently, despite the antagonistic genetic correlation between LSW and MWW.     

Examination of the relationship between the estrogen receptor gene and reproductive traits in swine

The relationship between estrogen receptor (ESR) genotype and reproductive traits in a population of Yorkshire, Large White, and crossbred animals was studied. Reproductive tract and litter data were analyzed for associations with ESR genotype, parity, and breed. Forty-six Yorkshire, 31 Large White, and 70 crossbred females from the above population were mated to Hampshire boars and slaughtered at 75 d of gestation. Data collected included ovulation rate, uterine horn length, number of fetuses, fetal weight, uterine weight, number of mummies, fetal sex, fetal placement, fetal survival, and fetal space. Data were analyzed using a model that included the fixed effects of ESR genotype, breed, parity, and all significant two-way interactions. Litter data representing 212 litter records were analyzed in a model that included the fixed effects of ESR genotype of dam, parity, farrowing month, dam breed, sire breed, and all significant two-way interactions. The ESR genotype was significantly associated with the total litter weight of piglets born and total litter weight of piglets born alive. Dams with the AA genotype had significantly (P = 0.04) heavier litters at birth (14.44 +/- 0.36 kg) than dams with the BB genotype (13.43 +/- 0.47 kg). Ovulation rate was significantly (P < 0.05) different between animals of parity 1 (17.22 +/- 0.41) and parity > or = 3 (19.92 +/- 0.85). Significant breed effects were observed for fetal weight, with purebred Large White animals having a greater fetal weight per horn (3,909 +/- 114 g) than purebred Yorkshire animals (3,553 +/- 92 g). Notable, but nonsignificant, trends with respect to ESR genotype were also observed for number of piglets alive at weaning and total litter weight at weaning. The ESR gene is positively associated with several previously uninvestigated reproductive traits.     

Phenotypic and genetic parameter estimates for reproductive traits in Zandi sheep

This study reports on the phenotypic and genetic (co)variance components for reproductive traits in Zandi sheep, using between 1,859 and 2,588 records obtained from 577 ewes. The data were collected from the Khojir Breeding Station of Zandi sheep in Tehran, Iran from 1994 to 2008. The basic traits were litter size at birth (LSB), litter size at weaning (LSW), litter mean weight per lamb born (LMWLB), and litter mean weight per lamb weaned (LMWLW), and the composite traits were total litter weight at birth (TLWB) and total litter weight at weaning (TLWW). Genetic analyses were carried out using the restricted maximum likelihood method that was explored by fitting the additive direct genetic effects and permanent environmental effects of the ewes as random effects and the ewe age at lambing and lambing year as fixed effects for all of the investigated traits. Akaike’s information criterion was used to choose the most appropriate model. LSB, LSW, LMWLB, LMWLW, TLWB, and TLWW direct heritability estimates were 0.07, 0.05, 0.12, 0.10, 0.08, and 0.14, respectively. The estimated fractions of variance due to the permanent environmental effects of the ewe ranged from 0.03 for LMWLB to 0.08 for LMWLW and TLWW. Corresponding repeatability estimates ranged from 0.10 for LSW to 0.22 for TLWW. Direct genetic correlations varied from ?0.61 for LSB–LMWLB to 0.88 for LSB–LSW and LSB–TLWB. Results indicate that genetic change depends not only on the heritability of traits, but also on the observed phenotypic variation; therefore, improvement of non-genetic factors should be included in the breeding programs.     

Genetic effects on ewe productivity of crossing D'man and Sardi breeds of sheep

Data from 364 ewes of Sardi (S), D'man (D), S x DS, DS x S, S x D, D x S (F1), F2, D x DS and DS x D breed groups mated to F1 rams were analyzed for fertility, number of lambs born alive, litter size at weaning, litter weight at weaning per ewe joined and mean lamb weight at 60 d. Each ewe was exposed in two seasons and had one or two lambings. Effects of breed group were significant for all traits. The highest number of lambs born alive and litter size at weaning were recorded in D'man (1.84 and 1.45, respectively) and D x DS (1.81 and 1.43, respectively). F1 ewes (S x D and D x S) had the highest fertility (.94) and litter weight at weaning per ewe exposed (13.8 kg). Mean lamb weight at 60 d was highest for S x DS and Sardi ewes (13.4 kg and 13.2 kg). D'man additive effects were positive and significant for number of lambs born alive, litter size at weaning and litter weight at weaning per ewe joined; were significant but negative for mean lamb weight at 60 d; and were not significant, although positive, for fertility. Significant individual heterosis was found for fertility, litter weight weaned and mean lamb weight at 60 d. Maternal heterosis and direct epistatic recombination effects were small for all traits.     

Estimation of genetic parameters for reproductive traits in shall sheep

The objective of this study was to estimate genetic parameters for reproductive traits in Shall sheep. Data included 1,316 records on reproductive performances of 395 Shall ewes from 41 sires and 136 dams which were collected from 2001 to 2007 in Shall breeding station in Qazvin province at the Northwest of Iran. Studied traits were litter size at birth (LSB), litter size at weaning (LSW), litter mean weight per lamb born (LMWLB), litter mean weight per lamb weaned (LMWLW), total litter weight at birth (TLWB), and total litter weight at weaning (TLWW). Test of significance to include fixed effects in the statistical model was performed using the general linear model procedure of SAS. The effects of lambing year and ewe age at lambing were significant (P?<?0.05). Genetic parameters were estimated using restricted maximum likelihood procedure, under repeatability animal models. Direct heritability estimates were 0.02, 0.01, 0.47, 0.40, 0.15, and 0.03 for LSB, LSW, LMWLB, LMWLW, TLWB, and TLWW, respectively, and corresponding repeatabilities were 0.02, 0.01, 0.73, 0.41, 0.27, and 0.03. Genetic correlation estimates between traits ranged from ?0.99 for LSW–LMWLW to 0.99 for LSB–TLWB, LSW–TLWB, and LSW–TLWW. Phenotypic correlations ranged from ?0.71 for LSB–LMWLW to 0.98 for LSB–TLWW and environmental correlations ranged from ?0.89 for LSB–LMWLW to 0.99 for LSB–TLWW. Results showed that the highest heritability estimates were for LMWLB and LMWLW suggesting that direct selection based on these traits could be effective. Also, strong positive genetic correlations of LMWLB and LMWLW with other traits may improve meat production efficiency in Shall sheep.     

Prediction and causation of litter market traits from preweaning and weaning characteristics in commercial meat rabbits

Market data on 1,315 rabbits from 201 litters from Californian (CAL), New Zealand White (NZW), CAL X NZW and NZW X CAL dams bred to CAL, NZW and Flemish Giant sires were subjected to multiple regression and path analyses. Market traits observed in litters at 56 d included average kit weight (A56W), litter size (LS56), total litter weight (L56W) and within-litter uniformity in individual weights (LCV). Preweaning variables as covariates included in the model were dam metabolic body weight (DMW), litter born (LSB), litter birth weight (LBW), milk yield from 1 to 21 d (MY) and feed intake from 1 to 28 d of the dam and litter (FI). Results from multiple regression analyses indicated linear and quadratic effects (P less than .20) due to LSB and MY for all four market characters. The LBW influenced (P less than .05) LS56 and L56W, and FI affected (P less than .05) LS56, L56W and LCV. Separate analyses were conducted involving 28-d weaning and feed intake variables as covariates: litter size weaned (LSW), litter weaning weight (LWW) and litter feed intake from 28 to 56 d (LFI). The three weaning covariates were important (P less than .05) for all market traits except LS56 (LWW was not significant). The most accurate regression equations were obtained from the weaning model for prediction of L56W and LS56 (R2 = .68 and .78). Path analyses revealed that preweaning covariates generally had direct rather than indirect effects on market traits. Both direct and indirect effects of weaning covariates were important for market traits. Results suggest that litter market traits of size and weight can be predicted with a reasonable degree of accuracy.     

Evaluating response to selection and nutritional needs in a three-way cross of rabbits

An experiment was carried out to evaluate the response obtained in a three‐way cross of rabbits when the lines involved had undergone within‐line selection for litter size or postweaning daily gain. The interaction between the level of nutrition and genetic level of the crossbreds was also studied. Using frozen embryos, old (H1) and current (H2) crossbred does and young were compared contemporarily. Does were fed a standard diet or a diet having high digestible energy and protein. The difference in the number of generations between lines used to produce both crosses were: 13 or 0 for the maternal lines, and 12 for the paternal line. The traits studied in the crossbred does were: daily feed intake during gestation, during the first 3 weeks of lactation and during the last week before weaning; doe weight at mating and at kindling; litter weight at birth and at weaning; total litter size, number born alive and litter size at weaning. The recorded traits for the young were: individual weight at weaning and at 63 days; individual daily gain after weaning; daily feed intake and feed conversion index. The last two traits were recorded as averages per cage. A total of 1161 litters from 190 does were involved. Significant differences in litter‐size traits, between H1 and H2 does, were observed and were higher than the expected from the within‐line response. The doe effect was not significant for other doe traits, adjusted to a constant litter size. The estimated difference in postweaning daily gain between H1 and H2 young was significant and in favour of H2, but the value was considerably lower than expected. The effect of type of feed and the interaction with the type of doe was not significant for any doe trait. The type of feed consumed by the doe was significant for postweaning daily gain, and the interaction with the type of crossbreds was significant for this trait and for individual weight at 63 days.     

Genetic and phenotypic aspects of early reproductive performance in Raeini Cashmere goats

This study used pedigree information and data collected from 1979 to 2012 at the Raeini Cashmere goat breeding station, located in Baft City in Kerman Province in southeastern Iran. Genetic and phenotypic parameters for early reproductive traits of breeding does, including total numbers of kids born at first kidding (LSB1), total numbers of kids weaned at first kidding (LSW1), total birth weight of all kids born at first kidding (LWB1), total weaning weight of all kids weaned at first kidding (LWW1), and age at first kidding (AFK), were estimated using a Bayesian approach via Gibbs sampling. Posterior means for heritability estimates of LSB1, LSW1, LWB1, LWW1, and AFK were statistically significant, with values of 0.12, 0.23, 0.17, 0.15, and 0.46, respectively. Low-to-moderate additive genetic variation was present for the studied reproductive traits. Estimated genetic correlations among LSB1, LSW1, LWB1, and LWW1 were statistically significant and ranged from 0.12 between LWB1 and LWW1 to 0.72 between LSB1 and LSW1. Corresponding phenotypic correlation estimates were also statistically significant and ranged from 0.04 between LWB1 and LWW1 to 0.55 between LSB1 and LSW1. Posterior means of genetic and phenotypic correlations between AFK and other studied traits were statistically significant only for LSB1 and LWB1. For LSB1, LSW1, LWB1, and LWW1, we conclude that genetic and phenotypic improvement in any of these traits in Raeini Cashmere does would favorably influence all of the other traits. However, does that first kidded at younger ages have smaller litters at birth and lower litter birth weights at their first parity.

     

Heritability and genetic correlation estimates of semen production traits with litter traits and pork production traits in purebred Duroc pigs

We estimated heritabilities of semen production traits and their genetic correlations with litter traits and pork production traits in purebred Duroc pigs. Semen production traits were semen volume, sperm concentration, proportion of morphologically normal sperms, total number of sperm, and total number of morphologically normal sperm. Litter traits at farrowing were total number born, number born alive, number stillborn, total litter weight at birth, mean litter weight at birth, and piglet survival rate at birth. Litter traits at weaning were litter size at weaning, total litter weight at weaning, mean litter weight at weaning, and piglet survival rate from birth to weaning. Pork production traits were average daily gain, backfat thickness, and loin muscle area. We analyzed 45,913 semen collection records of 896 boars, 6,950 farrowing performance records of 1,400 sows, 2,237 weaning performance records of 586 sows, and individual growth performance records of 9,550 animals measured at approximately 5 mo of age. Heritabilities were estimated using a single-trait animal model. Genetic correlations were estimated using a 2-trait animal model. Estimated heritabilities of semen production traits ranged from 0.20 for sperm concentration to 0.29 for semen volume and were equal to or higher than those of litter traits, ranging from 0.06 for number stillborn and piglet survival rate at birth to 0.25 for mean litter weight at birth, but lower than those of pork production traits, ranging from 0.50 for average daily gain to 0.63 for backfat thickness. In many cases, the absolute values of estimated genetic correlations between semen production traits and other traits were smaller than 0.3. These estimated genetic parameters provide useful information for establishing a comprehensive pig breeding scheme.     

大白猪、长白猪和杜洛克猪催乳素受体基因多态性及其与繁殖性能的关系

本试验通过PCR-RFLP技术对大白猪、长白猪和杜洛克猪的催乳素受体(prolactin receptor,PRLR)基因第10外显子AluⅠ酶切位点进行多态性分析,并对各基因型母猪的第1至第3胎次产仔数、产活仔数、断奶仔猪数、初生窝重、21日龄窝重及断奶成活率进行测定,进而分析PRLR基因多态性与繁殖性能的关系。结果表明,PRLR基因在3个品种中均存在多态位点,且AA基因型都是其优势基因型。关联分析结果表明,大白猪AA基因型个体第1、2和3胎各繁殖性状均呈现出高于AB和BB基因型的趋势。在繁殖性能已经稳定的第3胎次AA基因型个体产仔数、产活仔数、断奶仔猪数、初生窝重及断奶成活率比BB基因型个体平均分别高出0.31头、0.63头、0.02头、0.65 kg和0.43%,但差异均不显著(P>0.05)。     

Evaluation of candidate genes related to litter traits in Indian pig breeds

Improvement in litter traits is the key to profitable pig farming that directly enhances the economic standing of the farmers in developing countries. The present study aimed to explore oestrogen receptor (ESR), epidermal growth factor (EGF), follicle-stimulating hormone beta subunit (FSHβ), prolactin receptor (PRLR) and retinol-binding protein 4 (RBP4) genes as possible candidate genetic markers for litter traits in indigenous pigs of India. The breeds included in the study were Ghungroo, Mali, Niang Megha and Tenyi Vo, and the reproductive traits considered were litter size at birth (LSB), number born alive (NBA), litter weight at birth (LWB), litter size at weaning (LSW) and litter weight at weaning (LWW) at their first parity. PCR-RFLP and primer-based mutation detection methods were used to identify polymorphism, and associations between the genotypes and the traits were analysed using a general linear model. The Ghungroo pigs recorded the best litter performances among the breeds (p < .05, LWB p < .01). Different alleles and genotypes of the genes under study were detected. Short interspersed nuclear element (SINE) −/− genotype of FSHβ revealed significantly higher litter traits (p < .05, LSB p < .01). The LWW was also found to be significantly influenced by ESR BB and AB, EGF AB and BB, and PRLR CC genotypes (p < .05). Although we did not find statistically significant and consistently superior litter traits with respect to different genotypes of other studied genes than genotype SINE −/− of the FSHβ, PRLR CC genotype demonstrated superior performances for all the litter traits. Our study revealed the FSHβ as a potential candidate genetic marker for litter traits in indigenous pig breeds of India.     

Effects of genetic line and supplemental dietary fat on lactation performance of Duroc and Landrace sows.

A total of 124 Duroc and 99 Landrace primiparous and multiparous sows were assigned, within breed and contemporary group, to control (N) or 10% added fat (F) diets on d 105 of gestation based on parity and genetic line (control or selected for improved sow productivity), to determine the effects of genetic line and fat addition to the lactation diet on sow and litter performance. Weekly feed intake was not affected (P greater than .10) by genetic line for Duroc and Landrace sows but feed intake was reduced (P = .08) during wk 1 to 4 for Duroc sows and during wk 1 and 4 for Landrace sows (P less than .05) when they were fed diet F compared with diet N. Select (S)-line Duroc and Landrace sows lost more weight during lactation (P less than .01) than did control (C)-line sows. Select-line Landrace sows lost more backfat during lactation (P less than .05) than did C-line sows. Landrace sows lost less weight during lactation (P less than .05) when fed diet F than when fed diet N. The total number of pigs born, born alive, and alive at 21 d and at weaning were higher (P less than .01) for S-line Duroc sows, and litter size at 21 d and at weaning was higher (P less than .01) for S-line Landrace sows than for C-line litters within each breed. Pig survival from birth to weaning was increased (P = .07) for Duroc sows fed diet F but not for Landrace sows.(ABSTRACT TRUNCATED AT 250 WORDS)     

Genetic parameter estimates for growth traits and prolificacy in Raeini Cashmere goats

The main objectives of this study were to estimate genetic and phenotypic parameters for growth traits and prolificacy in the Raeini Cashmere goat. Traits included, birth weight (BWT), weaning weight (WWT), 6-month weight (6WT), 9-month weight (9WT), 12-month weight (12WT), average daily gain from birth to weaning (ADG1), average daily gain from weaning to 6WT (ADG2), average daily gain from 6WT to 12WT (ADG3), survival rate (SR), litter size at birth (LSB) and litter size at weaning (LSW) and total litter weight at birth (LWB). Data were collected over a period of 28 years (1982-2009) at the experimental breeding station of Raeini goat, southeast of Iran. Genetic parameters were estimated with univariate models using restricted maximum likelihood (REML) procedures. In addition to an animal model, sire and threshold models, using a logit link function, were used for analyses of SR. Age of dam, birth of type, sex and of kidding had significant influence (p < 0.05 or 0.01) all the traits. Direct heritability estimates were low for prolificacy traits (0.04 ± 0.01 for LSB, 0.09 ± 0.02 for LSW, 0.16 ± 0.02 for LWB and 0.05 ± 0.02 for SR) and average daily gain (0.12 ± 0.03 for ADG1, 0.08 ± 0.02 for ADG2, and 0.07 ± 0.03 for ADG3) to moderate for production traits (0.22 ± 0.02 for BWT, 0.25 ± 0.02 for WWT, 0.29 ± 0.04 for 6WT, 0.30 ± 0.02 for 9WT, 0.32 ± 0.05 for 12WT). The estimates for the maternal additive genetic variance ratios were lower than direct heritability for BWT (0.17 ± 0.03) and WWT (0.07 ± 0.02).     

Comparison of rabbit breed types for postweaning litter growth, feed efficiency, and survival performance traits

Postweaning data on 643 rabbits from 122 litters representing four breed types, New Zealand White (NZW) and Californian (CAL) purebreds, CAL X NZW (CXN), and Flemish Giant (FG) crossbreds (the latter group was a collection of FG X CAL, FG X Champagne D'Argent [CHA], and 1/2 FG X 1/4 CAL X 1/4 CHA), were gathered over five seasons and compared for growth, feed efficiency, and survival-related performance traits. Evaluation criteria included litter size and weight at weaning (28 d); 28- to 70-d litter feed intake, weight gain, feed efficiency, and mortality rate; and litter and average market weight (70 d). The least squares model included main effects of breed type, season of birth of the litter and parity of dam, litter size at weaning as a linear covariate, and the random error. Breed-type differences were not detected for litter size and weight at weaning and feed efficiency. Purebred NZW and CAL litter trait performances were comparable (P greater than .05). Purebred NZW litters consumed less feed than CXN and FG crosses, gained weight less rapidly than FG crosses, and weighed less per fryer at 70 d than CXN and FG crosses (P less than .05). Feed intake was lower and average market weight was lighter for CAL purebred litters than for CXN and FG crossbred litters (P less than .05). The CXN and FG crossbreds only differed (P less than .05) for average market weight (2,078 vs 2,192 g). Mortality rate was lower (P less than .05) in CXN crossbred litters than in CAL purebred litters.(ABSTRACT TRUNCATED AT 250 WORDS)     

Estimation of the additive and dominance variances in SA Duroc pigs

The objective of this study was to estimate dominance variance for number born alive (NBA), 21-day litter weight (LWT21) and interval between parities (FI) in South African Duroc pigs. A total of 10,703 NBA, 6883 LWT 21 and 6881 FI records were analysed. Bayesian analysis via Gibbs sampling was used to estimate variance components and genetic parameters. Estimates of additive genetic variance were 0.554, 16.84 and 4.535 for NBA, FI and LWT21, respectively. Corresponding estimates of dominance variance were 0.246, 9.572 and 0.661 respectively. Dominance effects were statistically not significant for all traits studied. Further research utilizing a larger data set is necessary to make concrete conclusions on the importance of dominance genetic effects for the traits studied.     

Within-litter variation of birth weight in hyperprolific Czech Large White sows and its relation to litter size traits, stillborn piglets and losses until weaning

Data from about 2900 litters (approximately 40,000 piglets) originating from 1063 Czech Large White hyperprolific sows were analyzed. The phenotypic and genetic relations between litter size traits, piglet mortality during farrowing and from birth to weaning and several statistics referring to the distribution of the birth weight within litter were analyzed. All genetic parameters were estimated from multi-trait animal models including the following factors: mating type (natural service or insemination), parity, linear and quadratic regression on age at first farrowing (1st litter) or farrowing interval (2nd and subsequent litters), herd-year-season effect and additive-genetic effect of the sow. The phenotypic correlations of the mean birth weight with the total number of piglets born and piglets born alive were − 0.30. Traits describing the variability of the birth weight within litter (range, variance, standard deviation, coefficient of variation) were mostly positively correlated with litter size. A statistically significant phenotypic correlation (− 0.09 to − 0.15) between mean birth weight and losses at birth and from birth to weaning was found. The heritability for the number of piglets born, piglets born alive and piglets weaned was around 0.15. The number of stillborn piglets had only a very low heritability less than 0.05, whereas the heritability for losses from birth to weaning was 0.13. The heritabilities of the mean, minimal and maximal birth weight were 0.16, 0.10 and 0.10, respectively. The heritability for all statistics and measures referring to the variability of the birth weight within litter was very low and did never exceed the value of 0.05. An increase in litter size was shown to be genetically connected with a decrease in the mean piglet birth weight and an increase in the within-litter variability of birth weight. Selection on litter size should be accompanied by selection on mortality traits and/or birth-weight traits. Losses from birth to weaning and the minimal birth weight in the litter were proposed as potential traits for a selection against piglet mortality.     

Effect of selection for growth traits on age and weight at puberty in bovine females

This 20-yr study, using 584 beef heifers born in the spring of 1984 or 1985, was conducted to determine whether selection for growth traits affected age and weight at puberty. Heifers were from three Hereford lines selected for weaning weight, final weight, and final weight plus muscling score, a control line and a line of Angus cattle. In addition, heifers from reciprocal crosses among the selection lines, control and Angus groups were evaluated. Intact bulls and androgenized heifers fitted with marking harnesses were used to aid in detection of estrus for heifers born in 1984 and 1985, respectively. The time of puberty was identified by the first behavioral estrus. During both years, heifers were weighed at 56-d intervals; these weights were used to calculate weight at puberty. Mean age at puberty was determined using survival analysis; percentages of heifers that were pubertal by the end of the study were transformed to logits for analysis. Heifers born in 1985 were heavier (P less than .05) at puberty than those born in 1984. Heifers in lines selected for growth traits were younger at puberty (P less than .05; 20 d) than were heifers in the control line because of combined direct and maternal genetic effects. Heifers from the final weight, control (P less than .05) and weaning weight lines (P less than .10) weighed less at puberty than Angus heifers; selection line x Angus crossbred heifers were heavier at puberty (P less than .05) than their respective pureline or purebred contemporaries due to heterotic effects. Selection for weaning weight, final weight or final weight plus muscling score did not have a detrimental effect on age at puberty in heifers.     

胎次对杜洛克、长白和大白母猪繁殖性能的影响

为了研究胎次对杜洛克、长白和大白母猪繁殖性能的影响,根据江苏省某国家级生猪核心育种场2009-2011年出生的繁殖母猪资料,分别选取128头杜洛克、681头长白和610头大白母猪共7280窝生产数据,统计分析不同胎次母猪的总产仔数、产活仔数、断奶仔猪数、初生窝重及校正21日龄窝重。此外,依据胎次将母猪分为3个繁殖阶段（1～2胎、3～6胎及7～8胎）来探究品种差异对母猪繁殖性能的影响。结果表明：胎次对母猪繁殖性能有显著影响（P<0.05）,母猪1～4胎的总产仔数、产活仔数、断奶仔猪数及初生窝重随胎次呈增加趋势,第4胎达到高峰,且显著高于其他胎次（P<0.05）;3～6胎繁殖性能较好,7胎之后出现迅速下降趋势;除在第4胎略有下降外,其他胎次的校正21日龄窝重随胎次递增。品种对母猪繁殖性能的影响显著（P<0.05）,长白和大白母猪的繁殖性能均极显著高于杜洛克母猪（P<0.01）;长白母猪的产活仔数和校正21日龄窝重显著高于大白母猪（P<0.05）,2个品种其他繁殖性能无显著差异（P＞0.05）。综上所述,杜洛克、长白和大白母猪的最佳繁殖胎次为3～6胎,长白猪的繁殖性能总体上优于大白猪,就本试验所在的育种场而言,长白猪可能更适合作为二元母猪生产中的母本。