Phenotypic and genetic variation in longevity of Polish Landrace sows

The influence of some production traits on the longevity of Polish Landrace sows was evaluated using survival analysis. Estimates of genetic parameters were obtained from the sire and animal components in linear and survival methodologies. Comparison between survival and linear models was based on heritabilities and ranking of estimated breeding values of sires. The same data set, 13 031 sows, was used for both methodologies, even in the presence of censored observations. The effects of herd*year and year*season of the first farrowing had the largest influence on the risk of culling of sows. Sows born in spring season (March–May) had a 24% (p < 0.001) lower hazard for removal than those born in winter (December–February). The age at first farrowing had a small but significant effect on culling: the hazard regression coefficient for this trait was 0.002 per day. Sows that had more piglets born alive and fewer stillborn in the first litter had a decreased risk of being culled. Within a contemporary group, slower growing gilts had decreased removal risk. The relative risk ratios show a marginal decreased rate of culling for sows with backfat thickness between 9.5 and 11 mm compared to the leaner sows. Loin depth had no effect on sow longevity. Heritability estimates ranged from 0.09 to 0.38 depending on the model and type of analysis. In survival analysis, all heritabilities for longevity were higher when analysed with sire models (0.21 and 0.38) compared to animal models (0.09 and 0.16). The use of animal or sire models in the linear analysis gave similar heritability estimates (0.12 and 0.10). Correlations between breeding values for sires were moderate and high, with absolute values from 0.51 to 0.99, depending on the model fitted and methodology. A stronger correlations within methodologies (0.83–0.99) than within models with different methodologies (0.51–0.63) were obtained.     

Need for sharp phenotypes in QTL detection for calving traits in dairy cattle

The aim of the study was to investigate whether parity‐specific phenotypes provide a clearer picture of quantitative trait loci (QTL) affecting calving traits in German Holsteins than breeding values estimated across parities. In experiment I, approximate daughter yield deviations were calculated by applying a univariate sire model assuming unrelated sires used as phenotypes in a QTL mapping study. These results were compared with those obtained using deregressed estimated breeding values obtained from the routine German sire evaluation (experiment II). In experiment I, 17 chromosome‐wise significant QTL were found for the first parity, but only 12 for the second parity. Only three QTL for maternal stillbirth, located on BTA7, 15 and 23, showed an experiment‐wise significance. Experiment II revealed 15 chromosome‐wise significant QTL. The results differed markedly between first and second parity within experiment I, as well as between experiment I and II. The present study showed that parity‐specific daughter yield deviations are beneficial for mapping QTL for calving traits. Furthermore, it is expected that the use of sharper phenotypes will also be advantageous for QTL fine mapping and the identification of candidate genes.     

Accessing genotype by environment interaction using within- and across-country test-day random regression sire models

First-lactation test-day (TD) milk records of Luxembourg and Tunisian Holsteins were analysed for evidence of genotype by environment interaction (G × E). The joint data included 730 810 TD records of 87 734 cows and 231 common sires. Random regression TD sire models with fourth-order Legendre polynomials were used to estimate genetic parameters via within- and across-country analyses. Daily heritability estimates of milk yield from within-country analysis were between 0.11 and 0.32, and 0.03 and 0.13 in Luxembourg and Tunisia, respectively. Heritability estimates for 305-day milk yield and persistency (defined as the breeding value for milk yield on DIM 280 minus the breeding value on DIM 80) were lower for Tunisian Holsteins compared with the Luxembourg population. Specifically, heritability for 305-day milk yield was 0.16 for within- and 0.11 for across-country analyses for Tunisian Holsteins and 0.38 for within- and 0.40 for across-country analyses for Luxembourg Holsteins. Heritability for apparent persistency was 0.02 for both within- and across-country analyses for Tunisian Holsteins and 0.08 for within- and 0.09 for across-country analyses for Luxembourg Holsteins. Genetic correlations between the two countries were 0.50 for 305-day milk yield and 0.43 for apparent persistency. Moreover, rank correlations between the estimated breeding values of common sires for 305-day milk yield and persistency, estimated separately in each country, were low. Low genetic correlations are evidence for G × E for milk yield production while low rank correlations suggest different rankings of sires in both environments. Results from this study indicate that milk production of daughters of the same sires depends greatly on the production environment and that importing high merit semen for limited input systems might not be an effective strategy to improve milk production.     

Comparison between genomic predictions using daughter yield deviation and conventional estimated breeding value as response variables

This study compared genomic predictions using conventional estimated breeding values (EBV) and daughter yield deviations (DYD) as response variables based on simulated data. Eight scenarios were simulated in regard to heritability (0.05 and 0.30), number of daughters per sire (30, 100, and unequal numbers with an average of 100 per sire) and numbers of genotyped sires (all or half of sires were genotyped). The simulated genome had a length of 1200 cM with 15,000 equally spaced Single-nucleotide polymorphism (SNP) markers and 500 randomly distributed Quantitative trait locus (QTL). In the simulated scenarios, the EBV approach was as effective as or slightly better than the DYD approach at predicting breeding value, dependent on simulated scenarios and statistical models. Applying a Bayesian common prior model (the same prior distribution of marker effect variance) and a linear mixed model (GBLUP), the EBV and DYD approaches provided similar genomic estimated breeding value (GEBV) reliabilities, except for scenarios with unequal numbers of daughters and half of sires without genotype, for which the EBV approach was superior to the DYD approach (by 1.2 and 2.4%). Using a Bayesian mixture prior model (mixture prior distribution of marker effect variance), the EBV approach resulted in slightly higher reliabilities of GEBV than the DYD approach (by 0.3-3.6% with an average of 1.9%), and more obvious in scenarios with low heritability, small or unequal numbers of daughters, and half of sires without genotype. Moreover, the results showed that the correlation between GEBV and conventional parent average (PA) was lower (corresponding to a relatively larger gain by including PA) when using the DYD approach than when using the EBV approach. Consequently, the two approaches led to similar reliability of an index combining GEBV and PA in most scenarios. These results indicate that EBV can be used as an alternative response variable for genomic prediction.     

Purebred-crossbred performance and genetic evaluation of postweaning growth and carcass traits in Bos indicus x Bos taurus crosses in Australia

Growth and carcass data on 7,154 cattle from a purebred project and 1,241 cattle from a crossbred project, comprising 916 first-crosses and 325 purebred Brahman controls, were analyzed to estimate genetic parameters, including the genetic correlations between purebred and crossbred performance (rpc). The data also allowed the estimation of sire breed means for various growth and carcass traits. Crossbred calves were produced using 9 Angus, 8 Hereford, 7 Shorthorn, 14 Belmont Red, and 8 Santa Gertrudis sires bred to Brahman dams. These same sires produced 1,568 progeny in a separate purebreeding project. Cattle in both projects were managed under two finishing regimens (pasture and feedlot) to representative market live weights of 400 (domestic), 520 (Korean), and 600 kg (Japanese). The traits studied included live weight at around 400 d of age (400W), hot carcass weight (CWT), retail beef yield percentage (RBY), intramuscular fat percentage (IMF), rump fat depth (P8), and preslaughter ultrasound scanned eye muscle area (SEMA). Estimated breeding values (EBV) of sires from their BREEDPLAN genetic evaluations were used to assess their value in predicting crossbred performance. Regressions of actual crossbred calf performance on sire EBV for each of the traits differed little from their expectation of 0.5. Angus sires produced crossbred carcasses with the highest P8 and lowest RBY but highest IMF. In contrast, crossbred progeny from Belmont Red sires had the lightest 400W and CWT, lowest P8, and highest RBY. Estimates of rpc were 0.48, 0.48, 0.83, 0.95, 1.00, and 0.78 for 400W, CWT, RBY, IMF, P8, and SEMA, respectively. Commercial breeders selecting sires for crossbreeding programs with Brahman females, based on EBV computed from purebred data, might encounter some reranking of sire's performance for weight-related traits, with little expected change in carcass traits.     

Genetic parameters for carcass traits of field progeny and their relationships with feed efficiency traits of their sire population for Japanese Black cattle

Genetic parameters for carcass traits of 1774 field progeny (1281 steers and 493 heifers), and their genetic relationships with feed efficiency traits of their sire population (740 bulls) were estimated with REML. Feed efficiency traits included feed conversion ratio (FCR) and residual feed intake (RFI). RFI was calculated by the residual of phenotypic (RFI_phe) and genetic (RFI_gen) regression from the multivariate analysis of feed intake on metabolic weight and daily gain. Progeny traits were carcass weight (CWT), rib eye area (REA), rib thickness (RBT), subcutaneous fat, yield estimate (YEM), marbling score (MSR), meat quality grade, meat color, fat color, meat firmness and meat texture. The estimated heritability for CWT (0.70) was high and heritabilities for all the other traits were moderate (ranged from 0.32 to 0.47), except for meat and fat color and meat texture which were low (ranged from 0.02 to 0.25). The high genetic correlation (0.62) between YEM and MSR suggests that simultaneous improvement of high carcass yield and beef marbling is possible. Estimated genetic correlations of RFI (RFI_phe and RFI_gen) of sires with CWT (− 0.60 and − 0.53) and MSR (− 0.62 and − 0.50) of their progeny were favorably negative indicating that the selection against RFI of sires may have contributed to produce heavier carcass and increase in beef marbling. The correlated responses in CWT, REA and RBT of progeny were higher to selection against RFI than those to selection against FCR of sires. This study provides evidence that selection against RFI is preferred over selection against FCR in sire population for getting better correlated responses in carcass traits of their progeny.     

Effect of sire mating patterns on future genetic merit and inbreeding in a closed beef cattle population

Summary Alternative breeding strategies were simulated based on the population structure of the Tajima strain of Japanese Black cattle. An analysis of the population structure revealed that some sires up to 20 years of age have been used in Tajima. In addition, 95% of newborn calves were the progeny of only 20 sires, and their mating frequencies were significantly skewed. The current average inbreeding coefficient and founder genome equivalents of the strain were estimated to be 0.199 and 2.25, respectively. Average inbreeding coefficient is expected to reach 0.394 within 27 years. Thus, different breeding strategies were assessed for their effect on the level of inbreeding and average genetic merit. We compared strategies that (1) halve the sire service period, (2) double the number of mating sires and (3) lower the skewed sire mating frequency and optimize the frequency for weighted genetic merit and diversity. Reducing the service period yielded a 7.0–12.0% reduction in the rate of inbreeding while maintaining almost the same genetic gain. Increasing the number of sires resulted in a 19.3–21.3% reduction in inbreeding with a corresponding 1.6–8.4% reduction in gain. The rates of inbreeding from the optimized strategies decreased as the weight on genetic diversity increased. However, a strategy that emphasized only genetic gain yielded lower gain than other strategies because the strategy allowed only one sire to mate, resulting in reduced genetic variance and low accuracy of genetic evaluation. In contrast, a strategy with no emphasis on genetic gain when determining mating frequency resulted in reductions of 16.0% and 63.2% in genetic gain and inbreeding, respectively. The strategies examined here are easily applicable and can be expected to reduce immediate loss of genetic diversity.     

Comparison of sire evaluation methods for carcass gain using field data

Four methods of predicting breeding values for carcass gain are compared: “regressed” least squares (RLSQ), mixed model (MM), mixed model with relationships among sires considered (MMR) and contemporary-comparison (CC). Very small changes in the ranking of the sires were observed from one method to another (rank correlations > 0.96). Consideration of the relationships among the sires or deleting the breed-group factor from the model did not lead to substantially different breeding values. The good correspondence of the predictors is mainly due to the well balanced distribution of the progeny over herds.     

Assessing genetic gain, inbreeding, and bias attributable to different flock genetic means in alternative sheep sire referencing schemes

Flocks participating in sire referencing schemes can achieve greater genetic gains than those achievable by within-flock selection. However, requirements for joining these schemes can be prohibitive to some producers. The objectives of this study were to determine whether less restrictive schemes or schemes of shorter duration could achieve rates of gain and reduce inbreeding as efficiently as continuous sire referencing schemes (SRS) and to investigate whether bias from different genetic means could be reduced by these alternative schemes. Pedigree and performance data for a single trait with a within-flock heritability of 0.25 were simulated (50 replications) for 15 flocks with 40 to 140 ewes per flock. Founder genetic means for each flock were sampled from a normal distribution with mean 0 and SD equal to the trait's genetic SD. After 10 yr of random mating, flocks had the opportunity to join an SRS and begin selection for the simulated trait. Yearling rams were chosen as reference sires randomly from the top one-sixth of the population ranked on BLUP EBV. Every year, in each flock, 3 reference sires were mated to 10 ewes. Six sire referencing scenarios were considered, in which all flocks participated in a SRS for 1) 15 yr; 2) 5 yr before discontinuing the scheme; 3) 10 yr before discontinuing the scheme; 4) 2 out of every 3 yr; 5) 15 yr with reference sire mating by natural service; and 6) no years (no use of SRS). Ewes not mated to reference sires were mated either to their own home-bred sires exclusively or to a mixture of homebred and unrelated purchased rams of unknown merit. Genetic gain was equivalent whether the SRS used AI or natural service matings, although inbreeding was lower with natural service. Across all scenarios, genetic gain and inbreeding were greater when excess ewes were mated exclusively to homebred sires. Genetic gains without SRS were 80 to 82% lower than when the scheme operated for 15 yr, whereas inbreeding was considerably greater. Other scenarios were intermediate in both gain and inbreeding levels. In all SRS scenarios, bias in EBV attributable to differing flock genetic means rapidly decreased in the first 5 yr of sire referencing. Levels of bias did not substantially increase when flocks discontinued SRS after 5 or 10 yr, suggesting that further participation in an SRS may not be necessary to manage risk. Natural service and noncontinuous SRS are viable options to continuous AI SRS in terms of genetic gain, inbreeding, and bias reduction.     

Genetic (co)variances and breeding value estimation of Gompertz growth curve parameters in Finnish Yorkshire boars, gilts and barrows.

This paper's objectives were to estimate the genetic (co)variance components of the Gompertz growth curve parameters and to evaluate the relationship of estimated breeding values (EBV) based on average daily gain (ADG) and Gompertz growth curves. Finnish Yorkshire central test station performance data was obtained from the Faba Breeding (Vantaa, Finland). The final data set included 121,488 weight records from 10,111 pigs. Heritability estimates for the Gompertz growth parameters mature weight (alpha), logarithm of mature weight to birth weight ratio (beta) and maturation rate (kappa) were 0.44, 0.55 and 0.31, respectively. Genotypic and phenotypic correlations between the growth curve parameters were high and mainly negative. The only positive relationship was found between alpha and beta. Pearson and Spearman rank correlation coefficients between EBV for ADG and daily gain calculated from Gompertz growth curves were 0.79. The Spearman rank correlation between the sire EBV for ADG and Gompertz growth curve parameter-based ADG for all sires with at least 15 progeny was 0.86. Growth curves differ significantly between individuals and this information could be utilized for selection purposes when improving growth rate in pigs.     

Simultaneous genetic evaluation of simulated mastitis susceptibility and recovery ability using a bivariate threshold sire model

The aim of this study was to develop a new approach for joint genetic evaluation of mastitis and recovery. Two mastitis incidences (0.28 and 0.95) measured via somatic cell count and three between traits genetic correlations (0.0, 0.2, and ?0.2) were simulated for daughter group sizes of 60 and 240. A transition model was applied to model transitions between healthy and disease state. The RJMC package in DMU was used to estimate (co)variances. Heritabilities were consistent with the simulated value (0.039) for susceptibility and a bit upward biased for recovery. Estimates of genetic correlations were ?0.055, 0.205, and ?0.192 for the simulated values of 0.0, 0.2, and ?0.2, respectively. For daughter group size of 60, accuracies of sire EBV ranged from 0.56 to 0.69 for mastitis and from 0.26 to 0.48 for recovery. The study demonstrated that both traits can be modeled jointly and simulated correlations could be correctly reproduced.     

Investigating maternal effects on production traits in Duroc pigs using animal and sire models

Variance components for production traits were estimated using different models to evaluate maternal effects. Data analysed were records from the South African pig performance testing scheme on 22 224 pigs from 18 herds, tested between 1990 and 2008. The traits analysed were backfat thickness (BFAT), test period weight gain (TPG), lifetime weight gain (LTG), test period feed conversion ratio (FCR) and age at slaughter (AGES). Data analyses were performed by REML procedures in ASREML, where random effects were successively fitted into animal and sire models to produce different models. The first animal model had one random effect, the direct genetic effects, while the additional random effects were maternal genetic and maternal permanent environmental effects. In the sire model, the random effects fitted were sire and maternal grand sire effects. The best model considered the covariance between direct and maternal genetic effects or between sire and maternal grand sire effects. Fitting maternal genetic effects into the animal model reduced total additive variance, while the total additive variance increased when maternal grand sire effects were fitted into the sire model. The correlations between direct and maternal genetic effects were all negative, indicating antagonism between these effects, hence the need to consider both effects in selection programmes. Direct genetic correlations were higher than other correlations, except for maternal genetic correlations of FCR with TPG, LTG and AGES. There has been direct genetic improvement and almost constant maternal ability in production traits as shown by trends for estimated (EBVs) and maternal breeding values (MBVs), while phenotypic trends were similar to those for EBVs. These results suggest that maternal genetic effects should be included in selection programmes for these production traits. Therefore, the animal–maternal model may be the most appropriate model to use when estimating genetic parameters for production traits in this population.     

Changes in connectedness over time in alternative sheep sire referencing schemes

A statistic to measure the level of connectedness achieved among flocks would help producers to assess the risk of comparing EBV of animals from different flocks. The objectives of this research were to evaluate the pattern of change over time in selected connectedness measures and to determine how effectively these measures quantify the level of risk due to potential bias in EBV comparisons across production units. Connectedness was evaluated using simulated sheep populations, with connections established using sire referencing schemes (SRS). Pedigree and performance data for a single trait with a within-flock heritability of 0.25 were simulated (50 replications) for 15 flocks with 40 to 140 ewes per flock. Genetic means for each flock were sampled from a normal distribution with mean 0 and SD equal to the trait's genetic SD. After 10 yr of random mating, flocks had opportunity to join a SRS and selection began for the simulated trait. Yearling rams were chosen as reference sires randomly from the top one-sixth of the population ranked on BLUP EBV. Every year, in each flock, 3 reference sires were mated to 10 ewes each. Six sire referencing scenarios (including no SRS) and 2 sources of nonreference sires were simulated. Connectedness was measured in 2 ways: (i) as the average prediction error correlation (r(ij)) of the flock genetic means (flock r(ij)) or the EBV for the current crop of ram lambs (lamb r(ij)) or (ii) as the average scaled prediction error variance of differences (PEVD) in flock genetic means (flock PEVD) or in lamb EBV in the current crop of ram lambs (lamb PEVD). Flock r(ij) increased linearly in all scenarios while SRS was underway and leveled off if the flocks discontinued SRS. Lamb r(ij) increased rapidly as soon as SRS began but decreased substantially if the flocks discontinued SRS. Behavior of flock PEVD and lamb PEVD measures were similar but in the opposite direction (i.e., PEVD decreased with increasing r(ij)). Within scenarios, both flock r(ij) and flock PEVD had a nonlinear relationship with bias in comparing animals across flocks. However, only flock r(ij) exhibited a consistent relationship across simulation scenarios. When flock r(ij) reached 0.05 and 0.10, approximately 20 and 10%, respectively, of the bias due to initial differences in flock genetic means remained. These levels of flock r(ij) are suggested as benchmark levels for minimizing the risk of comparing animal EBV among units.     

Lamb production performance of 14 sire breeds mated to New Zealand Bomney ewes

From an extensive series of trials involving approximately 15 000 Romney ewes mated with 435 rams, provisional results are presented on the comparative performance of 14 sire breeds for lamb meat production. The breeds, each represented by ten or more rams, were Southdown, Suffolk, South Suffolk, Hampshire, Dorset Down, South Dorset Down, Poll or Horn Dorset, Border Leicester, English Leicester, Ryeland, Cheviot, Lincoln, Merino and Romney.Important differences exist between sire breeds in progeny survival, with the Southdown being best and the Romney poorest. Progeny of long-wool sires, and particularly the Lincoln, clip more wool at post-weaning shearing than of the Down breeds, which exhibit quite small variation.Sire breeds vary in average live-weight and carcass growth of their progeny, the Suffolk, Hampshire and Dorset breeds producing the heaviest and Merino and Romney the lightest lambs. In terms of lamb live-weight or carcass production per Romney ewe mated, Romney, Merino, Lincoln, Ryeland, Cheviot and English Leicester sires are inferior to the Southdown while Dorset, Suffolk, South Suffolk and Dorset Down are superior.Within any breed, wide differences exist between progeny growth rates of the best and poorest sires, emphasising the importance of sound selection of rams and of adequate genetic sampling in breed comparisons.     

Top down preselection using marker assisted estimates of breeding values in dairy cattle

Top down preselection of young bulls before entering progeny testing has been proposed as a practicable form of marker‐assisted selection (MAS), especially in dairy cattle populations with large male paternal half‐sib families. Linkage phase between the superior (Q) and the inferior (q) QTL alleles of heterozygous sires (Qq at the QTL) with informative markers is established within each paternal half‐sib family and may be used for selection among grand‐progeny. If, additionally to sires, bulldams are also genotyped and data from consecutive generations are used, then a marker‐assisted best linear unbiased prediction (MA‐BLUP) model can be employed to connect the information of all generations and families of a top down design, and to select across all families. A customized ‘augmented’ sire model (with sires and dams of sires as random effects) is introduced for this purpose. Adapted formulae for the mixed model equations are given and their equivalence to a corresponding animal model and to a certain variant of previously proposed reduced animal models is shown. The application of the augmented sire model in MA‐BLUP estimation from daughter‐yield deviations and effective daughter contributions is presented.     

Changes of sires in a breeding farm enables maintenance of DNA‐level genetic variation in a produced herd of Hokkaido Native Horses

We investigated whether regular changes of the sire in a breeding farm of Hokkaido Native Horses (HKDs) enables the DNA‐level genetic variation of the produced animals to be maintained. The genotypes of 31 microsatellite markers were identified and analyzed in 207 animals produced in a breeding farm in which the sire was replaced every 3 to 5 years. The mean allele number indicating the degree of genetic variation was 5.97 and was similar to those reported previously. The mean observed heterozygosity was 0.74 and was higher than the expected heterozygosity, 0.69; F_IS was ?0.07, indicating that the analyzed animals reflected frequent outbreeding and had maintained genetic variation. Based on genetic structural analysis, the number of genetic subpopulations of the animals was estimated to be as 6, and the majority (more than 50%) of each subpopulation corresponded to the progeny of one of the sires used in the breeding farm; these observations suggested that genetic variation in the analyzed animals reflected the genetic differences among sires. Pedigree records indicated that the average co‐ancestry coefficient between sires used in the breeding farm was 0.015 corresponding to second cousin. This level of kinship among sires is acceptable for producing HKDs that maintain genetic variation.     

Estimation of genetic parameters based on individual and group mean records in laying hens

(1) The study was conducted to estimate the heritability, genetic correlations and breeding values of laying hens based on individual records and group mean records. (2) Records of two pure lines from a commercial breeding programme of White Leghorns from three generations housed in single cages and in group cages were used. A total of 8483 and 8817 individual records of lines A and D, respectively, and a total of 1358 (line A) and 1161 (line D) group mean records were analysed. (3) An animal model using Restricted Maximum Likelihood (REML) was used to estimate variance components of individual records. Group mean records were analysed using the sire model, taking heterogeneity of error variance and correlated residual effects into account. Breeding values of sires were estimated based on the BLUP method using a multivariate sire model. Spearman Rank correlations were used to compare sire breeding values estimated from individual records and from group mean records. The traits studied were monthly egg production, cumulative production and egg weight. (4) Heritability estimates based on individual records were higher than from group mean records. Heritabilities for cumulative production records were higher than for monthly production, based on individual as well as group mean records. The estimates of genetic correlations between monthly egg production and cumulative production were moderate to high. Egg production and egg weight recorded individually were highly genetically correlated with those recorded on group means. Sire breeding values estimated from individual records showed high correlations with those from group mean records. (5) Differences in the ranking of sire breeding values estimated from individual vs group mean records were negligible, indicating that no genotype x environment interaction exists. Selection based on individual performance records of laying hens housed in single cages could give a good response on performance of laying hens housed in group cages. Cumulative egg production over periods 1 to 6 is the best trait for the selection programme.     

Reproductive performance and genetic parameters in first cross ewes from different maternal genotypes

The reproduction of 2,846 crossbreed ewes with 7,899 records is reported. The ewes were progeny of mainly Merino dams and 91 sires from several maternal sire breeds including Border Leicester, East Friesian, Finnsheep, Coopworth, Corriedale, Booroola Leicester, and several others. There were 3 cohorts of ewes at each of 3 sites that were bred naturally to meat-type rams for each of 3 yr to evaluate reproduction and lamb production. At 2 sites, the ewes were mated in the autumn, first at 7 mo of age, and at 2 sites the ewes were mated in the spring, first at 14 or 17 mo of age. The cohorts of ewes and sites were genetically linked by 3 common sires. Mixed linear models were used to analyze ultrasound scanned pregnancy rate, fetal number, fertility (ewes lambing), litter size, lamb survival, number of lambs born (NLBj), number of lambs weaned (NLWj), and total weight of lamb weaned (TWWj) per ewe bred. Fixed effects included sire breed (1 to 10), environment (1 to 4, site and season of breeding: autumn, spring), breeding (1 to 3), cohort (1 to 3), and their interactions. The REML procedures were used to estimate (co)variance components. Ewe sire breed effects were significant (P < 0.01) for all the reproductive traits and breed means ranged from 0.75 to 0.96 for fertility, 1.22 to 2.08 for litter size, 0.70 to 0.90 for lamb survival, 0.99 to 1.66 for NLBj, 0.87 to 1.26 for NLWj, and 22.9 to 33.8 kg for TWWj, with the ranking of sire breeds varying for different traits. For all traits except lamb survival, the contrast between breeding 1 vs. 2 and 3 was considerably greater than the contrast between breeding 2 vs. 3, with significant environment x breeding interactions (P < 0.01). Estimates of heritability for the components of reproduction ranged from 0.03 +/- 0.02 for lamb survival to 0.19 +/- 0.05 for litter size, and those for the composite traits were 0.17 +/- 0.04 for NLBj, 0.13 +/- 0.04 for NLWj, and 0.17 +/- 0.04 for TWWj, with repeatability ranging from 0.10 to 0.19. Genetic and phenotypic correlations among the traits are reported. The significant variation among sire breeds of the crossbred ewes can be used to improve reproduction, although there was a change in the rank of the breeds for the various traits. There was considerable overlap between the breeds, and additional improvement could be achieved by exploiting the genetic variation between sires within breeds for all the ewe reproductive traits.     

Dairy sire evaluation fitting some of the herd-year-season effects as random

Three models of sire evaluation using different environmental groupings were compared. Effects fitted were herd, period (either 6 or 12 months) within herd, season (either 1 or 2 or 4 months) within period within herd, sire and linear and quadratic regressions on age at calving. Models differed in fitting (1) the effect of herd-period-season fixed, or (2) herd-period fixed and herd-period-season random, or (3) herd fixed, herd-period and herd-period-season random. The overall effects of period and season of calving were regarded as fixed, and were removed by precorrection. Records of first lactation fat yield on 49 242 progeny of 69 widely used proven Friesian-Holstein sires in 1628 herds in England and Wales were used.Compared to Model 1, Model 2 required about four-fifths and Model 3 required two-thirds of the effective number of daughters to give the equivalent variance of the estimates of sire effects. Using random effects models the relative advantage, in terms of a smaller variance of sire effects, increased as the size of herd-period-season subclass decreased.In herd-period-season fixed effects models subclasses with a single of few records, or subclasses with all or almost all records of the same sire, contribute nothing or little to the progeny group comparisons. The random effects models could avoid these losses, and were considered to be useful especially where herds are small, provided sires can be assumed as randomly distributed over environmental subclasses.