Experimental selection for calving ease and postnatal growth in seven cattle populations. I. Changes in estimated breeding values

Selection was used to create select and control lines within 4 purebred and 3 composite cattle populations. Both lines were selected for similar direct yearling weight and maternal weaning weight EBV. Select lines were selected for lower 2-yr-old heifer calving difficulty score EBV and control lines were selected for average birth weight EBV. Select (n = 6,926) and control (n = 2,043) line calves were born from 1993 through 1999 and selection began with the 1992 mating. High replacement rates resulted in 2,188 births to select line and 598 births to control line heifers. Data used to calculate EBV came from these populations and from 15 yr of data preceding the experiment. Calving difficulty was scored from 1 (no assistance) to 7 (cesarean). Calving difficulty scores from all twins, malpresentations, and cows 3 yr old and older were eliminated. Except for the first year, when a single-trait BLUP was used, a multiple-trait BLUP was used to calculate direct and maternal EBV for calving difficulty score, birth weight, and weaning weight, and direct EBV for postweaning gain. Sires (n = 498) were selected from those born in both the preceding populations and the select and control lines. In purebred populations, some industry sires (n = 88) were introduced based on their EPD. Tests of mean select and control line EBV differences of calves born in the final 2 yr were based on population variation. Select line direct EBV were 1.06 lower for heifer calving difficulty score (P < 0.001) and 3.5 kg lower (P < 0.001) for birth weight than controls. Average differences for other EBV were small and not significant. Yearling weight EBV was intentionally increased in both select and control lines of purebred populations. Angus, Hereford, Charolais, and Gelbvieh yearling weight EBV in control lines increased by 32.4, 27.2, 21.0, and 10.5 kg, respectively, from 1991 and 1992 to 1998 and 1999 compared with an average increase of 2.7 kg in composite populations. Birth weight direct EBV in purebred control lines increased by approximately 8% of yearling weight EBV increases. Selection based on a multiple-trait BLUP was able to create lines differing in calving difficulty score and birth weight EBV, but not in weaning weight and postweaning gain EBV. Differences between lines should be useful for evaluating BLUP and other traits and for identifying potential limitations of genetically decreasing calving difficulty score and birth weight.     

短芒披碱草异位保护群体的表型多样性研究

为揭示采集自川西北高原的短芒披碱草野生异位保存群体的表型变异规律,采用变异系数、巢式方差分析、主成分分析、聚类等方法,对川西北短芒披碱草种质资源共7个居群84个单株的32种表型性状进行多样性分析。结果表明,短芒披碱草表型性状在种群间和种群内存在极其丰富的多样性,种群间表型分化系数均值为41.66%,小于种群内变异(58.33%);茎秆、叶片、花序、小穗、颖片和内外稃的表型分化系数均值分别为55.92%,63.18%,38.62%,43.73%,31.45%和33.08%。穗部性状的稳定性较高。除第一颖长和外稃脉数外,其余性状与各地理生态因子间的相关性均不显著。利用群体间欧氏距离进行的UPGMA聚类分析结果表明,7个短芒披碱草野生群体可以划分为4类。Mantel相关分析表明地理距离与种群表型距离(欧氏距离)间相关不显著(r=0.334,P=0.083)。     

Genetic parameters for direct and maternal calving ease in Walloon dairy cattle based on linear and threshold models

Calving ease scores from Holstein dairy cattle in the Walloon Region of Belgium were analysed using univariate linear and threshold animal models. Variance components and derived genetic parameters were estimated from a data set including 33 155 calving records. Included in the models were season, herd and sex of calf × age of dam classes × group of calvings interaction as fixed effects, herd × year of calving, maternal permanent environment and animal direct and maternal additive genetic as random effects. Models were fitted with the genetic correlation between direct and maternal additive genetic effects either estimated or constrained to zero. Direct heritability for calving ease was approximately 8% with linear models and approximately 12% with threshold models. Maternal heritabilities were approximately 2 and 4%, respectively. Genetic correlation between direct and maternal additive effects was found to be not significantly different from zero. Models were compared in terms of goodness of fit and predictive ability. Criteria of comparison such as mean squared error, correlation between observed and predicted calving ease scores as well as between estimated breeding values were estimated from 85 118 calving records. The results provided few differences between linear and threshold models even though correlations between estimated breeding values from subsets of data for sires with progeny from linear model were 17 and 23% greater for direct and maternal genetic effects, respectively, than from threshold model. For the purpose of genetic evaluation for calving ease in Walloon Holstein dairy cattle, the linear animal model without covariance between direct and maternal additive effects was found to be the best choice.     

Estimation of ancestral inbreeding effects on stillbirth,calving ease and birthweight in German Holstein dairy cattle

In this study, the effect of different measurements of ancestral inbreeding on birthweight, calving ease and stillbirth were analysed. Three models were used to estimate the effect of ancestral inbreeding, and the estimated regression coefficient of phenotypic data on different measurements of ancestral inbreeding was used to quantify the effect of ancestral inbreeding. The first model included only one measurement of inbreeding, whereas the second model included the classical inbreeding coefficients and one alternative inbreeding coefficient. The third model included the classical inbreeding coefficients, the interaction between classical inbreeding and ancestral inbreeding, and the classical inbreeding coefficients of the dam. Phenotypic data for this study were collected from February 1998 to December 2008 on three large commercial milk farms. During this time, 36 477 calving events were recorded. All calves were weighed after birth, and 8.08% of the calves died within 48 h after calving. Calving ease was recorded on a scale between 1 and 4 (1 = easy birth, 4 = surgery), and 69.95, 20.91, 8.92 and 0.21% of the calvings were scored with 1, 2, 3 and 4, respectively. The average inbreeding coefficient of inbred animals was 0.03, and average ancestral inbreeding coefficients were 0.08 and 0.01, depending on how ancestral inbreeding was calculated. Approximately 26% of classically non‐inbred animals showed ancestral inbreeding. Correlations between different inbreeding coefficients ranged between 0.46 and 0.99. No significant effect of ancestral inbreeding was found for calving ease, because the number of animals with reasonable high level of ancestral inbreeding was too low. Significant effects of ancestral inbreeding were estimated for birthweight and stillbirth. Unfavourable effects of ancestral inbreeding were observed for birthweight. However, favourable purging effects were estimated for stillbirth, indicating that purging could be partly beneficial for genetic improvement of stillbirth.     

Genetic parameters for calving ease and survival at birth in Angus field data.

Calving performance records from the American Angus Herd Improvement Registry files were used to estimate variance components for calving ease and survival to 24 h. Genetic parameters for direct and maternal effects were estimated by using a sire-maternal grandsire model. Data included two independent samples of 19 and 34 herds with complete calving information. Maternal variance for calving ease was much larger than the variance for the direct effect of the sire. Maternal heritability for calving ease was .27 and .20 in the two samples of herds, respectively. Heritabilities for direct effects were .21 and .07. The genetic correlations between direct and maternal effects were -.93 and -.80. There was little genetic variation in survival at birth. Parameter estimates were within the allowable parameter space in the sample of 19 herds. Heritability for the direct effect of the sire on survival was .04. Maternal heritability was .09, and the direct-maternal correlation was -.85.     

Genetic relationships among calving ease, calving interval, birth weight, and weaning weight in the Asturiana de los Valles beef cattle breed

The aim of this paper was to estimate direct and maternal genetic parameters for calving ease (CE), birth weight (BrW), weaning weight (WW), and calving interval (CI) to assess the possibility of including this information in beef cattle improvement programs. Field data, including a total of 59,813 animals (1,390 sires and 1,147 maternal grand sires) from the Asturiana de los Valles beef cattle breed, were analyzed with a multivariate linear model. Estimates of heritability for direct genetic effects (CED, CID, BrWD, and WWD) were 0.191 +/- 0.019, 0.121 +/- 0.013, 0.390 +/- 0.030, and 0.453 +/- 0.035, respectively, whereas those for maternal genetic effects (CEM, BrWM, and WWM) were 0.140 +/- 0.015, 0.208 +/- 0.020, and 0.138 +/- 0.022, respectively. Genetic correlations between direct or maternal genetic effects across traits were, in general, positive and moderate to low. However, genetic correlation for the pair CED-BrWD was positive and high (0.604 +/- 0.064). Genetic correlations between the direct and maternal genetic effects within a trait were negative and moderate (-0.219 +/- 0.097 for CE, -0.337 +/- 0.080 for BrW, and -0.440 +/- 0.102 for WW). Genetic correlations for CED-BrWM and CED-WWM were -0.121 +/- 0.090 and -0.097 +/- 0.113, respectively. The genetic correlation for CEM-CID was unfavorable (0.485 +/- 0.078), and those for CEM-BrWD (-0.094 +/- 0.079) and CEM-WWD (-0.125 +/- 0.082) were low and negative. The genetic correlation between CID and WWM was favorable (-0.148 +/- 0.106). Overall, the data presented here support the hypothesis that maternal effects for CE and BrW are not the same and that the genetic relationships between CI and maternal effects for WW in beef cattle follow a similar pattern to that reported between CI and milk yield in dairy cattle. Moreover, the need to include direct and maternal breeding values in beef cattle selection programs is suggested.     

Genetic (co)variances for calving difficulty score in composite and parental populations of beef cattle: II. Reproductive, skeletal, and carcass traits

There is limited genetic information relating calving difficulty and body weights to other productive and reproductive traits. Such information is useful for specifying selection criteria and for predicting economic consequences of selection. Genetic, maternal, and environmental covariances of six productive and reproductive measurements with calving difficulty, birth weight, 200-d weight, and 168-d postweaning gain were estimated in 12 experimental populations of cattle. Calf (direct) genetic effects resulting in longer gestation length were associated with increased calving difficulty and birth weight. Maternal genetic effects of increased gestation length and heavier birth weight were significantly associated. Lighter birth weight and reduced calving difficulty were associated with earlier heifer age at puberty. Increases in direct genetic effects of calving difficulty, 200-d weight, and postweaning gain were associated with a small increase in direct effect of scrotal circumference. Increased direct genetic effects of scrotal circumference were correlated with maternal effects decreasing calving difficulty and increasing 200-d weight. Direct effects of the skeletal measurements, yearling hip height, and heifer pelvic area were positively correlated with direct effects of calving difficulty, birth weight, 200-d weight, and postweaning gain, positively correlated with maternal effects for birth weight and 200-d weight, and negatively correlated with maternal calving difficulty. Percentage of retail product was positively associated with calving difficulty and negatively associated with 168-d gain. Predicted genetic change in calving difficulty resulting from one standard deviation of selection for either calving difficulty score or birth weight was much larger than for any other traits. Selection for 200-d weight, 168-d postweaning gain, hip height, pelvic area, or scrotal circumference was predicted to have opposite effects on direct and maternal calving difficulty. Estimated genetic correlations indicate some small to moderate relationships between calving difficulty and the measured productive and reproductive traits. However, selection for reduced calving difficulty should be based on calving difficulty score and(or) birth weight because of their superiority in predicted genetic change.     

Linear–threshold animal model for birth weight, gestation length and calving ease in United Kingdom Limousin beef cattle data

Breeding value evaluation for UK Limousin beef cattle data was carried out by multiple-trait linear–threshold animal model with variance components assumed to be known. Polychotomous calving ease with five categories was analysed with two continuous traits: birth weight and gestation length. Field data consisted of 220,799 animals with observations with every possible combination of traits, and 270,035 animals in the pedigree. The threshold model was solved either with Newton Raphson or Expectation Maximisation algorithm, and solutions were compared to evaluation by a linear model with original and normalised scores. There were insignificant differences in solutions between the two algorithms for threshold model analyses. Furthermore, solutions of the continuous traits were similar by the threshold and linear models. For the categorical trait, correlations for random effects from the threshold and linear models were high. In case of normalised scores (original scores case in brackets) correlations with solutions from the threshold and linear model were 0.97 (0.94) and 0.97 (0.93) for direct and maternal genetic effects and 0.95 (0.89) for permanent maternal effects. Even so, at least one third of the top 1% ranking of bulls differed between the linear and the threshold models. Predictive abilities as correlations between estimated breeding values and pedigree indices were almost equal between the linear and threshold models for both continuous and categorical traits. In conclusion, despite the higher computational demand, the linear–threshold animal model can be seen worthwhile in the genetic evaluation of the national UK beef cattle data set.     

Threshold-linear versus linear-linear analysis of birth weight and calving ease using an animal model: II. Comparison of models.

Several models were evaluated in terms of predictive ability for calving difficulty. Data included birth weight and calving difficulty scores provided by the American Gelbvieh Association from 26,006 calves born to first-parity cows and five simulated populations of 6,200 animals each. Included in the model were fixed age of dam x sex interaction effects, random herd-year-season effects, and random animal direct and maternal effects. Bivariate linear-threshold and linear-linear models for birth weight/calving ease and univariate threshold and linear models for calving ease were applied to the data sets. For each data set and model, one-half of calving ease records were randomly discarded. Predictive ability of the different models was defined with the mean square error (MSE) for the difference between a deleted calving ease score and its prediction obtained from the remaining data. In terms of correlation between simulated and predicted breeding values, the threshold models had a 1% advantage for direct genetic effects and 3% for maternal genetic effects. In simulation, the average MSE was .29 for linear-threshold, .32 for linear-linear, .37 for threshold, and .39 for linear model. For the field data set, the MSE was .31, .33, .39, and .40, respectively. Although the bivariate models for calving ease/birth weight were more accurate than univariate models, the threshold models showed a greater advantage under the bivariate model. For the purpose of genetic evaluation for calving difficulty in beef cattle, the use of the linear-threshold model seems justified. In dairy cattle, the evaluation for calving ease can benefit from recording birth weight.     

Phenotypic differences in Schistosoma mattheei ova from populations sympatric and allopatric to S. haematobium

Schistosoma mattheei ova were collected from cattle in different localities in South Africa and after hatching, miracidia were used to infest Bulinus (Physopsis) globosus. Cercariae harvested from these snails were used to infest the definitive host Praomys (Mastomys) coucha and eggs from the resulting female S. mattheei were collected. These ova were compared with a Schistosoma haematobium X S. mattheei hybrid similarly collected from an infested P. (M.) coucha. The results indicate that S. mattheei populations which are sympatric to S. haematobium possess S. haematobium characteristics. It is suggested that the gene pools of populations of the parasite in these areas are infiltrated with S. haematobium genes via the S. mattheei X S. haematobium hybrid originating from human hosts.     

Selection for weaning weight and postweaning gain in Hereford cattle. II. Response to selection

Single trait selection was practiced in three lines of Hereford cattle at two locations. Bulls were selected within sire families for increased weaning weight (WW) in the WW line (WWL), for postweaning gain (PG) in the PG line (PGL) and at random in the control line (CTL). Data include the performance of 2,467 calves produced from 1967 to 1981. Environmental effects were estimated from CTL (method I) and from multiple regression procedures (method II). Phenotypic and environmental time trends were negative for WW and generally were positive for PG. Estimated genetic gains for WW in WWL were 1.07 +/- .51 kg/yr in bulls and .62 +/- .36 kg/yr in heifers using method I and .50 +/- .31 kg/yr in bulls and .10 +/- .17 kg/yr in heifers using method II. Corresponding values for PG in PGL were .85 +/- .40 and 1.03 +/- .24 kg/yr in bulls and .30 +/- .28 and .37 +/- .12 kg in heifers. Correlated genetic gains for WW in PGL were larger than direct WW gains, whereas genetic gains for PG in WWL were smaller than direct PG gains. From method I, estimates of realized heritability (h2R) for WW were .31 +/- .18 in bulls and .22 +/- .13 in heifers. For PG, h2R was .31 +/- .13 in bulls and .06 +/- .12 in heifers. Using method II, h2R for WW was .09 +/- .08 in bulls and .02 +/- .07 in heifers. Corresponding values for PG were .29 +/- .10 and .11 +/- .08. Joint estimates of the realized genetic correlation between WW and PG were .69 +/- .18 and .46 +/- .31 for methods I and II, respectively. Variation in selection response was evaluated using quasi-replicates. Results of this study indicate that selection for PG improved both WW and PG faster than selection for WW.     

Bayesian inference strategies for the prediction of genetic merit using threshold models with an application to calving ease scores in Italian Piemontese cattle

First parity calving difficulty scores from Italian Piemontese cattle were analysed using a threshold mixed effects model. The model included the fixed effects of age of dam and sex of calf and their interaction and the random effects of sire, maternal grandsire, and herd‐year‐season. Covariances between sire and maternal grandsire effects were modelled using a numerator relationship matrix based on male ancestors. Field data consisted of 23 953 records collected between 1989 and 1998 from 4741 herd‐year‐seasons. Variance and covariance components were estimated using two alternative approximate marginal maximum likelihood (MML) methods, one based on expectation‐maximization (EM) and the other based on Laplacian integration. Inferences were compared to those based on three separate runs or sequences of Markov Chain Monte Carlo (MCMC) sampling in order to assess the validity of approximate MML estimates derived from data with similar size and design structure. Point estimates of direct heritability were 0.24, 0.25 and 0.26 for EM, Laplacian and MCMC (posterior mean), respectively, whereas corresponding maternal heritability estimates were 0.10, 0.11 and 0.12, respectively. The covariance between additive direct and maternal effects was found to be not different from zero based on MCMC‐derived confidence sets. The conventional joint modal estimates of sire effects and associated standard errors based on MML estimates of variance and covariance components differed little from the respective posterior means and standard deviations derived from MCMC. Therefore, there may be little need to pursue computation‐intensive MCMC methods for inference on genetic parameters and genetic merits using conventional threshold sire and maternal grandsire models for large datasets on calving ease.     

Evaluation models and genetic parameters for calving difficulty in beef cattle

Calving difficulty was analyzed under threshold and linear models considering either a fixed or random herd-year effect. The aim of the study was to compare models for predicting breeding values according to the size of herd-year groups. When simulating data sets with small herds, in order to obtain an unbiased evaluation under a nonrandom and negative association of sire and herd effects, the best model for a practical evaluation was the fixed linear model. Field data included 246,576 records of the largest Charolais herds in France. Models were compared using the correlations of estimated breeding values between the different models. Although the best model from a theoretical point of view was a threshold model with a fixed herd-year effect, a linear model with a fixed herd-year effect was the best choice from a practical point of view for predicting direct effects for calving difficulty in beef cattle and was a sufficient choice for predicting the associated maternal effects for data set with large herds. Correlations between direct estimated breeding values under the reference model and the fixed linear model and the random threshold model were 0.94 and 0.91, respectively. Correlations between the corresponding maternal estimated breeding values were 0.94 and 0.98. Heritabilities of direct effects were 0.27 and 0.14 under fixed threshold and fixed linear models, respectively. The corresponding heritabilities of maternal effects were 0.18 and 0.13, and the genetic correlation between direct and maternal effects were -0.36 and -0.34, respectively.     

Genome-wide detection of signatures of selection in three Valdostana cattle populations

The Valdostana is a local dual purpose cattle breed developed in Italy. Three populations are recognized within this breed, based on coat colour, production level, morphology and temperament: Valdostana Red Pied (VPR), Valdostana Black Pied (VPN) and Valdostana Chestnut (VCA). Here, we investigated putative genomic regions under selection among these three populations using the Bovine 50K SNP array by combining three different statistical methods based either on allele frequencies (F_ST) or extended haplotype homozygosity (iHS and Rsb). In total, 8, 5 and 8 chromosomes harbouring 13, 13 and 16 genomic regions potentially under selection were identified by at least two approaches in VPR, VPN and VCA, respectively. Most of these candidate regions were population-specific but we found one common genomic region spanning 2.38 Mb on BTA06 which either overlaps or is located close to runs of homozygosity islands detected in the three populations. This region included inter alia two well-known genes: KDR, a well-established coat colour gene, and CLOCK, which plays a central role in positive regulation of inflammatory response and in the regulation of the mammalian circadian rhythm. The other candidate regions identified harboured genes associated mainly with milk and meat traits as well as genes involved in immune response/inflammation or associated with behavioural traits. This last category of genes was mainly identified in VCA, which is selected for fighting ability. Overall, our results provide, for the first time, a glimpse into regions of the genome targeted by selection in Valdostana cattle. Finally, this study illustrates the relevance of using multiple complementary approaches to identify genomic regions putatively under selection in livestock.     

Genetic parameters for direct and maternal calving ability over parities in Piedmontese cattle

Estimates of heritabilities and genetic correlations for calving ease over parities were obtained for the Italian Piedmontese population using animal models. Field data were calving records of 50,721 first- and 44,148 second-parity females and 142,869 records of 38,213 cows of second or later parity. Calving ability was scored in five categories and analyzed using either a univariate or a bivariate linear model, treating performance over parities as different traits. The bivariate model was used to investigate the genetic relationship between first- and second- or between first- and third-parity calving ability. All models included direct and maternal genetic effects, which were assumed to be mutually correlated. (Co)variance components were estimated using restricted maximum likelihood procedures. In the univariate analyses, the heritability for direct effects was .19 +/- .01, .10 +/- .01, and .08 +/- .004 for first, second, and second and later parities, respectively. The heritability for maternal effects was .09 +/- .01, .11 +/- .01, and .05 +/- .01, respectively. All genetic correlations between direct and maternal effects were negative, ranging from -.55 to -.43. Approximated standard errors of genetic correlations between direct and maternal effects ranged from .041 to .062. For multiparous cows, the fraction of total variance due to the permanent environment was greater than the maternal heritability. With bivariate models, direct heritability for first parity was smaller than the corresponding univariate estimate, ranging from .18 to .14. Maternal heritabilities were slightly higher than the corresponding univariate estimates. Genetic correlation between first and second parity was .998 +/- .00 for direct effects and .913 +/- .01 for maternal effects. When the bivariate model analyzed first- and third-parity calving ability, genetic correlation was .907 +/- .02 for direct effects and .979 +/- .01 for maternal effects. Residual correlations were low in all bivariate analyses, ranging from .13 for analysis of first and second parity to .07 for analysis of first and third parity. In conclusion, estimates of genetic correlations for calving ease in different parities obtained in this study were very high, but variance components and heritabilities were clearly heterogeneous over parities.     

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.     

Genetic parameters and genetic trends for age at first calving and calving interval in an Angus-Blanco Orejinegro-Zebu multibreed cattle population in Colombia

Genetic parameters and genetic trends for age at first calving (AFC), interval between first and second calving (CI1), and interval between second and third calving (CI2) were estimated in a Colombian beef cattle population composed of Angus, Blanco Orejinegro, and Zebu straightbred and crossbred animals. Data were analyzed using a multiple trait mixed model procedures. Estimates of variance components and genetic parameters were obtained by Restricted Maximum Likelihood. The 3-trait model included the fixed effects of contemporary group (year-season of calving-sex of calf; sex of calf for CI1 and CI2 only), age at calving (CI1 and CI2 only), breed genetic effects (as a function of breed fractions of cows), and individual heterosis (as a function of cow heterozygosity). Random effects for AFC, CI1, and CI2 were cow and residual. Program AIREMLF90 was used to perform computations. Estimates of heritabilities for additive genetic effects were 0.15 ± 0.13 for AFC, 0.11 ± 0.06 for CI1, and 0.18 ± 0.11 for CI2. Low heritabilities suggested that nutrition and reproductive management should be improved to allow fuller expressions of these traits. The correlations between additive genetic effects for AFC and CI1 (0.33 ± 0.41) and for AFC and CI2 (0.40 ± 0.36) were moderate and favorable, suggesting that selection of heifers for AFC would also improve calving interval. Trends were negative for predicted cow yearly means for AFC, CI1, and CI2 from 1989 to 2004. The steepest negative trend was for cow AFC means likely due to the introduction of Angus and Blanco Orejinegro cattle into this population.     

Genetic relationships between calving and carcass traits for Charolais and Hereford cattle in Sweden

The objective of this study was to estimate genetic correlations between calving difficulty score and carcass traits in Charolais and Hereford cattle, treating first and later parity calvings as different traits. Genetic correlations between birth weight and carcass traits were also estimated. Field data on 59,182 Charolais and 27,051 Hereford calvings, and carcass traits of 5,260 Charolais and 1,232 Hereford bulls, were used in bivariate linear animal model analyses. Estimated heritabilities were moderate to high (0.22 to 0.50) for direct effects on birth weight, carcass weight, and (S)EUROP (European Community scale for carcass classification) grades for carcass fleshiness and fatness. Heritabilities of 0.07 to 0.18 were estimated for maternal effect on birth weight, and for direct and maternal effects on calving difficulty score at first parity. Lower heritabilities (0.01 to 0.05) were estimated for calving difficulty score at later parities. Carcass weight was positively genetically correlated (0.11 to 0.53) with both direct and maternal effects on birth weight and with direct effects on calving difficulty score. Carcass weight was, however, weakly or negatively (-0.70 to 0.07) correlated with maternal calving difficulty score. Higher carcass fatness grade was genetically associated with lower birth weight, and in most cases, also with less difficult calving. Genetic correlations with carcass fleshiness grade were highly variable. Moderately unfavorable correlations between carcass fleshiness grade and maternal calving difficulty score at first parity were estimated for both Charolais (0.42) and Hereford (0.54). This study found certain antagonistic genetic relationships between calving performance and carcass traits for both Charolais and Hereford cattle. Both direct and maternal calving performance, as well as carcass traits, should be included in the breeding goal and selected for in beef breeds.