Individual efficiency for the use of feed resources in rabbits

A Bayesian procedure, which allows consideration of the individual variation in the feed resource allocation pattern, is described and implemented in 2 sire lines of rabbit (Caldes and R). The procedure is based on a hierarchical Bayesian scheme, where the first stage of the model consists of a multiple regression model of feed intake on metabolic BW and BW gain. In a second stage, an animal model was assumed including batch, parity order, litter size, and common environmental litter effects. Animals were reared during the fattening period (from weaning at 32 d of age to 60 d of age) in individual cages on an experimental farm, and were fed ad libitum with a commercial diet. Body weight (g) and cumulative feed intake (g) were recorded weekly. Individual BW gain (g) and average BW (ABW, g) were calculated from these data for each 7-d period. Metabolic BW (g(0.75)) was estimated as ABW(0.75). The number of animals actually measured was 444 and 445 in the Caldes and R lines, respectively. Marginal posterior distributions of the genetic parameters were obtained by Gibbs sampling. Posterior means (posterior SD) for heritabilities for partial coefficients of regression of feed intake on metabolic BW and feed intake on BW gain were estimated to be 0.35 (0.17) and 0.40 (0.17), respectively, in the Caldes line and 0.26 (0.19) and 0.27 (0.14), respectively, in line R. The estimated posterior means (posterior SD) for the proportion of the phenotypic variance due to common litter environmental effects of the same coefficients of regression were respectively, 0.39 (0.14) and 0.28 (0.13) in the Caldes line and 0.44 (0.22) and 0.49 (0.14) in line R. These results suggest that efficiency of use of feed resources could be improved by including these coefficients in an index of selection.     

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.     

Correlated responses of pre- and postweaning growth and backfat thickness to six generations of selection for ovulation rate or prenatal survival in French Large White pigs

Correlated effects of selection for components of litter size on growth and backfat thickness were estimated using data from 3 pig lines derived from the same base population of Large White. Two lines were selected for 6 generations on either high ovulation rate at puberty (OR) or high prenatal survival corrected for ovulation rate in the first 2 parities (PS). The third line was an unselected control (C). Genetic parameters for individual piglet BW at birth (IWB); at 3 wk of age (IW3W); and at weaning (IWW); ADG from birth to weaning (ADGBW), from weaning to 10 wk of age (ADGPW), and from 25 to 90 kg of BW (ADGT); and age (AGET) and average backfat thickness (ABT) at 90 kg of BW were estimated using REML methodology applied to a multivariate animal model. In addition to fixed effects, the model included the common environment of birth litter, as well as direct and maternal additive genetic effects as random effects. Genetic trends were estimated by computing differences between OR or PS and C lines at each generation using both least squares (LS) and mixed model (MM) methodology. Average genetic trends for direct and maternal effects were computed by regressing line differences on generation number. Estimates of direct and maternal heritabilities were, respectively, 0.10, 0.12, 0.20, 0.24, and 0.41, and 0.17, 0.33, 0.32, 0.41, and 0.21 (SE = 0.03 to 0.04) for IWB, IW3W, IWW, ADGBW, and ADGPW. Genetic correlations between direct and maternal effects were moderately negative for IWB (-0.21 +/- 0.18), but larger for the 4 other traits (-0.59 to -0.74). Maternal effects were nonsignificant and were removed from the final analyses of ADGT, AGET, and ABT. Direct heritability estimates were 0.34, 0.46, and 0.21 (SE = 0.03 to 0.05) for ADGT, AGET, and ABT, respectively. Direct and maternal genetic correlations of OR with performance traits were nonsignificant, with the exception of maternal correlations with IWB (-0.28 +/- 0.13) and ADGPW (0.23 +/- 0.11) and direct correlation with AGET (-0.23 +/- 0.09). Prenatal survival also had low direct but moderate to strong maternal genetic correlations (-0.34 to -0.65) with performance traits. The only significant genetic trends were a negative maternal trend for IBW in the OR line and favorable direct trends for postweaning growth (ADGT and AGET) in both lines. Selection for components of litter size has limited effects on growth and backfat thickness, although it slightly reduces birth weight and improves postweaning growth.     

Correlated responses for litter traits to six generations of selection for ovulation rate or prenatal survival in French Large White pigs

Effects of selection for reproductive traits were estimated using data from 3 pig lines derived from the same Large White population base. Two lines were selected for 6 generations on high ovulation rate at puberty (OR line) or high prenatal survival corrected for ovulation rate in the first 2 parities (PS line). The third line was an unselected control line. Genetic parameters for age and BW at puberty (AP and WP); number of piglets born alive, weaned, and nurtured (NBA, NW, and NN, respectively); proportions of stillbirth (PSB) and survival from birth to weaning (PSW); litter and average piglet BW at birth (LWB and AWB), at 21 d (LW21 and AW21), and at weaning (LWW and AWW) were estimated using REML methodology. Heritability estimates were 0.38 +/- 0.03, 0.46 +/- 0.03, 0.16 +/- 0.01, 0.08 +/- 0.01, 0.09 +/- 0.01, 0.04 +/- 0.01, 0.04 +/- 0.02, 0.19 +/- 0.02, 0.10 +/- 0.02, 0.10 +/- 0.02, 0.36 +/- 0.02, 0.27 +/- 0.01, and 0.24 +/- 0.01 for AP, WP, NBA, PSB, NW, NN, PSW, LWB, LW21, LWW, AWB, AW21, and AWW, respectively. The measures of litter size showed strong genetic correlations (r(a) >/= 0.95) and had antagonistic relations with PSB (r(a) = -0.59 to -0.75) and average piglet BW (r(a) = -0.19 to -0.46). They also had strong positive genetic correlations with prenatal survival (r(a) = 0.67 to 0.78) and moderate ones with ovulation rate (r(a) = 0.36 to 0.42). Correlations of litter size with PSW were negative at birth but positive at weaning. The OR and PS lines were negatively related to PSW and average piglet BW. Puberty traits had positive genetic correlations with OR and negative ones with PS. Genetic trends were estimated by computing differences between OR or PS and control lines at each generation using least squares and mixed model methodologies. Average genetic trends were computed by regressing line differences on generation number. Significant (P < 0.05) average genetic trends were obtained in OR and PS lines for AP (respectively, 2.1 +/- 0.9 and 3.2 +/- 1.0 d/generation) and WP (respectively, 2.0 +/- 0.5 and 1.8 +/- 0.5 d/generation) and in the PS line for NBA (0.22 +/- 0.10 piglet/generation). Tendencies (P < 0.10) were also observed for LWB (0.21 +/- 0.12 kg/generation) and AWW (-0.25 +/- 0.14 kg/generation) in the PS line. Selection on components of litter size can be used to improve litter size at birth, but result in undesirable trends for preweaning survival.     

Correlated response in litter size components in rabbits selected for litter size variability

A divergent selection experiment for the environmental variability of litter size (Ve) over seven generations was carried out in rabbits at the University Miguel Hernández of Elche. The Ve was estimated as the phenotypic variance within the female, after correcting for year‐season and parity‐lactation status. The aim of this study was to analyse the correlated responses to selection in litter size components. The ovulation rate (OR) and number of implanted embryos (IE) in females were measured by laparoscopy at 12 day of the second gestation. At the end of the second gestation, the total number of kits born was measured (TB). Embryonic (ES), foetal (FS) and prenatal (PS) survival were computed as IE/OR, TB/IE and TB/OR, respectively. A total of 405 laparoscopies were performed. Data were analysed using Bayesian methodology. The correlated response to selection for litter size environmental variability in terms of the litter size components was estimated as either genetic trends, estimated by computing the average estimated breeding values for each generation and each line, or the phenotypic differences between lines. The OR was similar in both lines. However, after seven generations of selection, the homogenous line showed more IE (1.09 embryos for genetic means and 1.23 embryos for phenotypic means) and higher ES than the heterogeneous one (0.07 for genetic means and 0.08 for phenotypic means). The probability of the phenotypic differences between lines being higher than zero (p) was 1.00 and .99, respectively. A higher uterine overcrowding of embryos in the homogeneous line did not penalize FS; as a result, this line continued to show a greater TB (1.01 kits for genetic means and 1.30 kits for phenotypic means, p = .99, in the seventh generation). In conclusion, a decrease in litter size variability showed a favourable effect on ES and led to a higher litter size at birth.     

Responses to 19 generations of litter size selection in the Nebraska Index line. I. Reproductive responses estimated in pure line and crossbred litters

Our objective was to estimate responses in reproductive traits in the Nebraska Index line (I) after 19 generations of selection for increased litter size. Responses were estimated in dams producing pure line, F1, and three-way cross litters. A total of 850 litters were produced over six year-seasons, including 224 pure line litters, 393 F1 litters produced from I and C females mated with Danbred NA Landrace (L) or Duroc-Hampshire (T) boars, and 233 litters by F1 L x I and L x C females mated with T boars. Contrasts of means were used to estimate the genetic difference between I and C and interactions of line differences with mating type. Farrowing rates of lines I (u = 91.0%) and C (u = 92.8%) did not differ. Averaged across all genetic groups, mean number born alive per litter was 10.1 pigs, and number and weight of pigs weaned per litter, both adjusted for number nursed and weaning age of 12 d, were 9.7 pigs and 34.4 kg, respectively. Averaged across mating types, direct genetic effects of I were greater than C (P < 0.05) for total born (3.53 pigs), number born alive (2.53 pigs), number of mummified pigs (0.22 pig), and litter birth weight (2.14 kg). The direct genetic effect of line I was less than C (P < 0.05) for litter weaning weight (-1.88 kg). Interactions of line effects with crossing system were significant (P < 0.05) for total number born, number of stillborn pigs, number weaned, and litter weaning weight. In pure line litters, I exceeded C by 4.18 total pigs and 1.76 stillborn pigs per litter, whereas the estimate of I-C in F1 litters was 2.74 total pigs and 0.78 stillborn pig per litter. The contrast between I and C for number weaned and litter weaning weight in pure litters was 0.32 pig and -0.28 kg, respectively, compared with 0.25 pig and -2.14 kg in F1 litters. Crossbreeding is an effective way to use the enhanced reproductive efficiency of the Index line.     

Genetics of osteochondral disease and its relationship with meat quality and quantity, growth, and feed conversion traits in pigs

The main objective of this research was to estimate heritabilities of seven osteochondrosis (OC) lesions in station-tested pigs and their genetic and phenotypic correlations with four meat quality (MQ) traits, the percentage of premium cuts (PPC), daily weight gain (DWG), and feed conversion ratio (FCR). Observed OC lesions were on the head of humerus (HK), condylus medialis humeri (CMH), condylus lateralis humeri (CLH), radius and ulna proximal (RUP), distal epiphyseal cartilage of ulna (DEU), head of femur (FK), and condylus medialis femoris (CMF). Meat quality traits were i.m. fat (IMF), muscle pH at 1 h after slaughter (pH1), muscle pH at 30 h after slaughter (pH30), and light reflectance on muscle (H30). The data set comprised 2,710 animals, of which 1,291 animals had OC records. All traits were analyzed by multiple-trait linear mixed model, with the animal's genetic and common litter effects as random. Fixed effects in the model varied between traits. Each OC lesion was further analyzed by a univariate generalized linear mixed model or, equivalently, "threshold models," assuming logistic, probit (normal), and Poisson distributions of the underlying "liability" to the disease. For OC lesions, estimates of heritability were low on the original "incidence" scale (0.06 for HK to 0.16 for CLH) and moderate to high on the liability scale (0.08 to 0.42). Genetic correlations (r(g)) between OC lesions and most MQ traits and PPC were generally unfavorable. Significant r(g) were -0.44 for DWG-CMH, 0.31 for DWG-CMF, 0.40 for FCR-HK, 0.21 for PPC-CLH, 0.32 for PPC-RUP, 0.30 for PPC-CMF, -0.54 for pH1-CLH, 0.47 for pH1-DEU, -0.34 for pH30-CMH, 0.58 for pH30-DEU, -0.50 for H30-HK, -0.31 for H30-DEU, and 0.31 for H30-CMF. Genetic susceptibilities to some OC lesions within the front leg were positively related to each other (r(g) range = 0.57 to 0.69), but r(g) between front and hind leg OC lesions were mostly negative (range = -0.21 to -0.40). Estimated h2 was 0.60 for PPC, and ranged from 0.12 to 0.66 for MQ traits, 0.28 for DWG, and 0.42 for FCR. Genetic correlations among meat quality and quantity traits ranged from -0.66 to 0.37. This is the first study to report genetic and phenotypic correlations between OC lesions and several meat quality and quantity traits in pigs. These findings will be useful to pig industry, especially in designing breeding programs for robust pigs.     

Bayesian estimates of genetic parameters for metritis, retained placenta, milk fever, and clinical mastitis in Holstein dairy cows via Gibbs sampling

The objective of this study was to estimate heritability and genetic correlations between the liabilities of clinical mastitis (CM), milk fever (MF), metritis (MET), and retained placenta (RP) within the first three lactations of Holstein dairy cows. The records of 57,301 dairy cows from 20 large dairy herds in Iran between January 2005 and June 2009 were analysed with univariate and bivariate threshold animal models, using Gibbs sampling methodology. The final model included the fixed class effects of herd-year, season of calving, parity of dam, the linear covariate effect of age at calving, and the random direct genetic effect of animal. Posterior means of heritability for liabilities in first, second, and third lactations were 0.06, 0.08, and 0.09, respectively, for CM; 0.10, 0.12, and 0.11, respectively, for MF; 0.09, 0.07, and 0.10, respectively, for MET, and 0.07, 0.08, and 0.08, respectively, for RP. Posterior means of genetic correlations between disease liabilities were low or moderate (from −0.01 to 0.26). The results of this study indicated the importance of health traits for considering in the selection index of Iranian Holstein dairy cows.     

Genetics of litter size in three maternal lines of rabbits: repeatability versus multiple-trait models

Variance components were estimated in 3 lines of rabbits selected for litter size at weaning (A, Prat, and V) to test one of the assumptions of the models used for selection: that litter size data at different parities are repeated measurements of the same trait. Multiple-trait analyses were performed for the total number of kits born (TB), the number of kits born alive (BA), and the number of kits weaned (NW) per litter. Estimates were obtained by REML in multivariate analyses, including all of the information of the selection criteria, under a repeatability model or a multiple-trait model, considering litter size at the first, second, and subsequent parities as different traits. Models included the fixed effects of the physiological status of the female and the year-season of mating day, buck and doe random permanent environmental effects, and doe additive genetic effects. Results indicated that prolificacy was determined mainly by doe components and that the service sire had a very small effect. Heritabilities for the first and second parities were greater than the estimates obtained under the repeatability model (0.04 to 0.14 for the repeatability model). In the A and V lines, similar values of heritability were found at the first and second parities, but in the Prat line heritability at the second parity was always greater than at the first and greater parities (values of 0.21, 0.17, and 0.15 for TB, BA, and NW, respectively, in second parities of the Prat line). Genetic correlations between the same traits at different parities were approximately 0.8 for all traits in line A, but much lower in the other 2 lines. On average, the values were 0.64 for TB, 0.48 for BA, and 0.39 for NW between the first and second parities, and 0.65 for TB, 0.56 for BA, and 0.45 for NW between the first and third and greater parities. Genetic correlations between the second and greater parities showed the greatest values (approximately 0.8) in lines A and Prat for all traits, but they were lower in line V (0.63 for BA and 0.37 for NW). The heterogeneity of heritabilities and genetic correlations between parities lower than 0.9 suggests that litter size at different parities could be considered as different traits when genetic evaluations are performed. However, when the accuracies of predicted breeding values under a multiple-trait and a repeatability model were calculated, assuming the first to be the true model, the values obtained were nearly the same for all traits in all lines.     

Reproductive performance in a diallel cross among lines of mice selected for litter size and body weight

Genetic factors affecting female reproductive performance in lines of mice with a known history of selection were estimated from a 5 X 5 diallel cross. Lines were selected as follows: large litter size at birth (L+); large 6-wk body weight (W+); an index for large litter size and small 6-wk body weight (L+W-); the complementary index (L-W+) and randomly (K). Partitioning of direct and correlated responses for litter size, 6-wk body weight and related traits into average direct genetic (li) and average maternal genetic (mi) effects indicated that the magnitude of differences in li exceeded those in mi. Lines having positive responses in li were W+ greater than L+ greater than L-W+ for dam body weight, L+ greater than L+W- greater than W+ for litter size and L+ greater than (W+, L+W-) for litter birth weight, whereas L-W+ responded negatively for litter size. A positive association was found between mi for litter size and dam body weight, W+ and L-W+ being high and L+ and L+W- low for both traits. Female infertility and time from male exposure to parturition had relatively small correlated responses. Line rankings in general combining ability (gi) and net line effects were similar for the respective traits. Depending upon the line and trait involved, the relative contribution of average direct genetic and line direct heterotic (hi) effects to general combining ability [gi = (1/2) li + hi] varied. Line heterosis refers to average heterosis in crosses involving that line. Direct heterosis ( hij ) for each trait differed considerably among crosses. The three crosses showing the highest hij for litter size at birth, W+ X L-W+ (1.78), L+ X W+ (1.28) and L-W+ X L+W- (1.22), possibly had loci contributing directional dominance to litter size with frequencies of parental lines deviating in opposite directions relative to mean gene frequency. The correlation between absolute difference in parental line means and hij for litter size was not significant, suggesting that the magnitudes of absolute differences in parental means were not reliable predictors of divergence in gene frequency. Crossbred performance increased linearly with midparent values for litter size at birth (b = .88 +/- .09, R2 = .92) and dam parturition body weight (b = 1.13 +/- .04, R2 = .99), the latter trait showing an increase (P less than .01) in heterosis as midparent values increased.     

Direct and correlated responses to two-stage selection for ovulation rate and number of fully formed pigs at birth in swine

Our objectives were to estimate responses and genetic parameters for ovulation rate, number of fully formed pigs at birth, and other production traits following two-stage selection for increased ovulation rate and number of fully formed pigs. Eight generations of selection were practiced in each of two lines. One selection line was derived from a line that previously selected eight generations for an index to increase ovulation rate and embryonic survival (the IOL pigs). The other selection line was derived from the unselected control line of the index selection experiment (the COL pigs). The control line (C) was continued with random selection. Due to previous selection, Line IOL had greater ovulation rate (4.24 +/- 0.38 and 4.14 +/- 0.29 ova) and litter size (1.97 +/- 0.39 and 1.06 +/- 0.38 pigs) at Generation 0 of two-stage selection than did Lines COL and C. In Stage 1, all gilts from 50% of the largest litters were retained. Approximately 50% of them were selected for ovulation rate in Stage 2. Gilts selected for ovulation rate were mated to boars selected from the upper one-third of the litters for litter size. At Generations 7 and 8, differences in mean EBV for ovulation rate and litter size between Lines IOL and C were 6.20 +/- 0.29 ova and 4.66 +/- 0.38 pigs; differences between Lines COL and C were 2.26 +/- 0.29 ova and 2.79 +/- 0.39 pigs; and differences between Lines IOL and COL were 3.94 +/- 0.26 ova and 1.86 +/- 0.39 pigs. Regressions of line mean EBV on generation number were 0.27 +/- 0.07 ova and 0.35 +/- 0.06 pigs in Line IOL; 0.30 +/- 0.06 ova and 0.29 +/- 0.05 pigs in Line COL; and 0.01 +/- 0.07 ova and 0.02 +/- 0.05 pigs in Line C. Correlated responses were decreased age at puberty and increased number of pigs born alive, number of mummified pigs, prenatal loss, and individual and litter birth weight. Two-stage selection for ovulation rate and number of pigs per litter is a promising procedure to improve litter size in swine.     

不同品系家兔的RAPD遗传分析

应用随机扩增多态ＤＮＡ技术（ＲＡＰＤ）对新西兰白兔、加利福尼亚兔、布列塔尼亚配套系（ＥＬＣＯ）进行了遗传分析。从２０个随机引物中筛选出８个,对其基因组ＤＮＡ进行ＰＣＲ扩增,对扩增产物进行琼脂糖凝胶电泳,共检测到７１条扩增片段,其中多态片段４５条,占６３．４％,反映了家兔品种的遗传变异。多态性统计表明：品种内的遗传相似度大于品种间的遗传相似度。聚类分析表明：ＥＬＣＯ的Ｄ系与新西兰白兔、加利福尼亚兔的     

Direct and maternal genetic differences between lines of mice selected for body weight and litter size: traits of dams

Genetic differences in performance of dams were estimated by linear contrasts using means of two selected lines of mice and reciprocal F1's, F2's and backcrosses. The lines were selected for increased 6-wk body weight (W) or increased litter size (L). Genetic differences estimated were direct average (gD), direct heterosis (hD), maternal average (gM), progeny average (gP), and progeny heterosis (hP). For dam weight and feed consumption from 12 to 21 d postpartum (pp), gD was the largest genetic difference and favored line W. For litter size, litter weight at birth, litter efficiency (litter weight gain/dam feed consumption) from birth to 12 d pp and within litter mortality from 1 to 21 d pp, gD favored L and, except for hD in litter efficiency, was the most important genetic difference for these traits. Direct heterosis was the only significant difference for litter weight at 21 d pp, litter efficiency from 12 to 21 d pp and within litter mortality at parturition. The gM were larger in W than in L for dam weight and feed consumption, and for litter size and weight at birth, but they were usually of smaller magnitude than gD. The gP were significant only in litter traits measured before 12 d pp and favored W. For no trait measured was hP of consequence. Line differences in dam and litter weight accounted for genetic differences in dam feed consumption. Genetic differences in litter size at birth were not due to line differences in dam weight. The lower mortality within litters nursed by crossbred dams was responsible for hD on litter weight and litter efficiency. Within but not among lines, higher mortality rates were associated with larger litters.     

Reproductive performance of chimeric mice produced from genetic lines that differ in litter size

A population of chimeras was made by aggregating 8- and 16-cell embryos from two mouse strains: a randomly bred line (C) and a selected line characterized by large litters (JU), with litter sizes of 7.7 and 13.5, respectively. The two genotypes were developmentally "balanced", as judged by the high frequency (90%) of chimeras with an intermediate or high degree of coat-color chimerism, a chimeric sex ratio of 2.2:1 males:females, and a high percentage of chimeras (31% of males, 71% of females) with germ cells of both strains. Litter size characteristics, including ovulation rate, implantation rate, rates of pre- and postimplantation embryo survival and number born were studied in the female chimeras and compared with the performance of both parent lines and to the genetic cross of the two lines. Values for JU females exceeded those for C females for all parameters studied except postimplantation embryo survival, which was the same for both lines in second litters and was lower for JU's third litters. For most traits, means for genetic crossbreds and chimeras were similar, regardless of whether the means were at or above the midparent average. In contrast, for ovulation rate and body weight, genetic crossbreds and chimeras clearly differed, with chimeric females being similar to the JU line and genetic crossbred females exhibiting additive inheritance. Because of phenotypic differences between experimental chimeras and crossbreds produced from the same two lines, chimeras may provide a useful model for studying the physiologic basis for expression of genetic differences in quantitative traits.     

Selection for food conversion in broilers: Direct and correlated responses to selection for body‐weight gain,food consumption and food conversion ratio

1. Direct and correlated responses were determined after five generations in four lines of chickens selected either for increased body‐weight gain (line W), for increased food consumption (line F), for decreased food conversion ratio (line E), or at random (line C).

2. Realised heritability estimates calculated after five generations of selection were : 0–37 + 0.04 for weight gain (WG); 0.44 + 0.05 for food consumption (FC); 0.21 + 0.04 for food conversion ratio (FCR).

3. Realised genetic correlation estimates were: WG and FC, +0.71 ±006; WG and FCR, ‐0.40±0.09; FC and FCR, +0.27 + 0.09.

4. Zero‐generation heritability and genetic correlation estimates were greater than the realised estimates, and sex linkage appeared to be important in the expression of all three traits.

5. The genetic correlation between FC and FCR was asymmetrical with considerable positive response in FCR in line F (r_g = +0.79) but negligible response in FC in line E (r_g = —0.01).

6. There was an apparent plateau in response in FCR in line E from the third to the fifth selected generations.     

The National Pork Producers Council Maternal Line National Genetic Evaluation Program: a comparison of six maternal genetic lines for female productivity measures over four parities

Litter (n = 8,424) and female performance records were collected in two breed-to-wean production units in order to evaluate genetic line differences for sow longevity and maternal performance over four parities. Lines evaluated were American Diamond Genetics, Danbred North America, Dekalb-Monsanto DK44, Dekalb-Monsanto GPK347, Newsham Hybrids, and National Swine Registry. Females within a line were derived from a minimum of 65 sires, 197 dams (three dams per sire), and a maximum of three daughters per dam, except in the GPK347, which were produced using semen from 12 Nebraska Index boars mated with Dekalb-Monsanto Line 34 females. All lines expressed 100% maternal heterosis. Mixed model statistical procedures were used with fixed effects including genetic line, parity, production unit, and two-way interactions. Random effects included a contemporary week of production and female for repeated records. Lactation length (average 15 d) was included as a linear covariate where appropriate. In total, 3,599 females entered as early-weaned pigs, 3,283 entered the breeding herd, 2,592 farrowed at least a single litter, and 1,656 and completed four parities. Line (P < 0.001) and parity (P < 0.001) effects were observed for virtually all traits measured. Ranges of genetic line differences averaged across parities were 1.76 pigs for total born, 1.45 pigs born alive, and 0.31 stillborn pigs per litter. Ranges of line differences in total and live litter weight were 1.4 and 1.3 kg, respectively. Ranges among lines, within Parities 1 through 4, for litter size at weaning were 0.56, 1.08, 0.91, and 0.64 pigs per litter, respectively. Line differences for weight (33.8 kg) and backfat depth (6.4 mm) at farrowing, lactation feed intake (8.7 kg), weight loss (5.0 kg), and backfat loss (0.87 mm) were observed. Extended wean-to-estrus interval was related to variation in weight, feed intake, and backfat loss in all lines except the GPK347. The GPK347 females farrowed and weaned the largest number of pigs, ate less feed in lactation, and lost more backfat and weight during lactation, yet they had the largest litters and the shortest wean-to-estrus intervals. Line x parity interactions existed for many traits due to small rank changes, but in general, the high- and low-ranked lines did not change. Genetic line differences in reproductive efficiency through four parities exist and must be recognized when choosing a female line.     

Comparison of repeatability and multiple trait threshold models for litter size in sheep using observed and simulated data in Bayesian analyses

Bayesian analyses were used to estimate genetic parameters on 5580 records of litter size in the first four parities from 1758 Mule ewes. To examine the appropriateness of fitting repeatability (RM) or multiple trait threshold models (MTM) to litter size of different parities, both models were used to estimate genetic parameters on the observed data and were thereafter compared in a simulation study. Posterior means of the heritabilities of litter size in different parities using a MTM ranged from 0.12 to 0.18 and were higher than the heritability based on the RM (0.08). Posterior means of the genetic correlations between litter sizes of different parities were positive and ranged from 0.24 to 0.71. Data sets were simulated based on the same pedigree structure and genetic parameters of the Mule ewe population obtained from both models. The simulation showed that the relative loss in accuracy and increase in mean squared error (MSE) was substantially higher when using the RM, given that the parameters estimated from the observed data using the opposite model are the true parameters. In contrast, Bayesian information criterion (BIC) selected the RM as most appropriate model given the data because of substantial penalty for the higher number of parameters to be estimated in the MTM model. In conclusion, when the relative change in accuracy and MSE is of main interest for estimation of breeding values of litter size of different parities, the MTM is recommended for the given population. When reduction in risk of using the wrong model is the main aim, the BIC suggest that the RM is the most appropriate model.     

Bayesian threshold analysis of direct and maternal genetic parameters for piglet mortality at farrowing in Large White, Landrace, and Pietrain populations

A Bayesian threshold model was fitted to analyze the genetic parameters for farrowing mortality at the piglet level in Large White, Landrace, and Pietrain populations. Field data were collected between 1999 and 2006. They were provided by 3 pig selection nucleus farms of a commercial breeding company registered in the Spanish Pig Data Bank (BDporc). Analyses were performed on 3 data sets of Large White (60,535 piglets born from 4,551 litters), Landrace (57,987 piglets from 5,008 litters), and Pietrain (42,707 piglets from 4,328 litters) populations. In the analysis, farrowing mortality was considered as a binary trait at the piglet level and scored as 1 (alive piglet) or 0 (dead piglet) at farrowing or within the first 12 h of life. Each breed was analyzed separately, and operational models included systematic effects (year-season, sex, litter size, and order of parity), direct and maternal additive genetic effects, and common litter effects. Analyses were performed by Bayesian methods using Gibbs sampling. The posterior means of direct heritability were 0.02, 0.06, and 0.10, and the posterior means of maternal heritability were 0.05, 0.13, and 0.06 for Large White, Landrace, and Pietrain populations, respectively. The posterior means of genetic correlation between the direct and maternal genetic effects for Landrace and Pietrain populations were -0.56 and -0.53, and the highest posterior intervals at 95% did not include zero. In contrast, the posterior mean of the genetic correlation between direct and maternal effects was 0.15 in the Large White population, with the null correlation included in the highest posterior interval at 95%. These results suggest that the genetic model of evaluation for the Landrace and Pietrain populations should include direct and maternal genetic effects, whereas farrowing mortality could be considered as a sow trait in the Large White population.     

Role of inbreeding depression,non‐inbred dominance deviations and random year‐season effect in genetic trends for prolificacy in closed rabbit lines

In closed rabbit lines selected for prolificacy at the Polytechnic University of Valencia, genetic responses are predicted using BLUP. With a standard additive BLUP model and year‐season (YS) effects fitted as fixed, genetic trends were overestimated compared to responses estimated using control populations obtained from frozen embryos. In these lines, there is a confounding between genetic trend, YS effects and inbreeding, and the role of dominance is uncertain. This is a common situation in data from reproductively closed selection lines. This paper fits different genetic evaluation models to data of these lines, aiming to identify the source of these biases: dominance, inbreeding depression and/or an ill‐conditioned model due to the strong collinearity between YS, inbreeding and genetic trend. The study involved three maternal lines (A, V and H) and analysed two traits, total born (TB) and the number of kits at weaning (NW). Models fitting YS effect as fixed or random were implemented, in addition to additive genetic, permanent environment effects and non‐inbred dominance deviations effects. When YS was fitted as a fixed effect, the genetic trends were overestimated compared to control populations, inbreeding had an apparent positive effect on litter size and the environmental trends were negative. When YS was fitted as random, the genetic trends were compatible with control populations results, inbreeding had a negative effect (lower prolificacy) and environmental trends were flat. The model fitting random YS, inbreeding and non‐inbred dominance deviations yielded the following ratios of additive and dominance variances to total variance for NW: 0.06 and 0.01 for line A, 0.06 and 0.00 for line V and 0.01 and 0.08 for line H. Except for line H, dominance deviations seem to be of low relevance. When it is confounded with inbreeding as in these lines, fitting YS effect as random allows correct estimation of genetic trends.     

Genetic correlations between two strains of Durocs and crossbreds from differing production environments for slaughter traits

The aim of this study was to estimate the genetic correlations between 2 purebred Duroc pig populations (P1 and P2) and their terminal crossbreds [C1 = P1 x (Landrace x Large White) and C2 = P2 x (Landrace x Large White)] raised in different production environments. The traits analyzed were backfat (BF), muscle depth (MD), BW at slaughter (WGT), and weight per day of age (WDA). Data sets from P1, P2, C1, and C2 included 26,674, 8,266, 16,806, and 12,350 animals, respectively. Two-trait models (nucleus and commercial crossbreds) for each group included fixed (contemporary group, sex, weight, and age), random additive (animal for P1 and P2 and sire for C1 and C2), random litter, and random dam (C1 and C2 only) effects. Heritability estimates (+/-SE) for BF were 0.46 +/- 0.04, 0.38 +/- 0.02, 0.32 +/- 0.02, and 0.33 +/- 0.02 for P1, P2, C1, and C2, respectively. Heritability estimates for MD were 0.31 +/- 0.01, 0.23 +/- 0.02, 0.19 +/- 0.01, and 0.12 +/- 0.01 for P1, P2, C1, and C2, respectively. The estimates for WGT and WDA were 0.31 +/- 0.01, 0.21 +/- 0.02, 0.16 +/- 0.01, and 0.18 +/- 0.01 and 0.32 +/- 0.01, 0.22 +/- 0.02, 0.16 +/- 0.01, and 0.19 +/- 0.01, respectively. Genetic correlations between purebreds and crossbreds for BF were 0.83 +/- 0.09 (P1 x C1) and 0.89 +/- 0.05 (P2 x C2), for MD 0.78 +/- 0.05 (P1 x C1) and 0.80 +/- 0.08 (P2 x C2). For WGT and WDA, the correlations were 0.53 +/- 0.08 (P1 x C1), 0.80 +/- 0.10 (P2 x C2), and 0.60 +/- 0.07 (P1 x C1) and 0.79 +/- 0.09 (P2 x C2), respectively. (Co)variances in crossbreds were adjusted to a live BW scale. Compared with purebreds, the genetic variances in crossbreds were lower, and the residual variances were greater. Sire variances in crossbreds were approximately 20 to 30% of the animal variances in purebreds for BF and MD but were 13 to 25% for WGT and WDA. The efficiency of purebred selection on crossbreds, assessed by EBV prediction weights, ranged from 0.43 to 0.91 for line 1 and 0.70 to 0.92 for line 2. When nucleus and commercial environments differ substantially, the efficiency of selection varies by line and traits, and selection strategies that include crossbred data from typical production environments may therefore be desirable.