Genetic evaluation of crossbred Bos indicus cow temperament at parturition.

Cow temperament at parturition may be mostly a measure of aggressiveness. The heritability of cow temperament at parturition in Bos taurus cows has been reported to be low. The objectives of this study were to estimate the heritability of cow temperament at parturition, conduct a genome-wide association analysis of cow temperament at the time of parturition, and estimate the correspondence of cow temperament at the time of parturition with cow productive performance and early-life temperament traits in Bos indicus crossbreds. Cow temperament was assessed from 1 to 5 indicating increasing levels of aggressiveness of cows (937 cows and 4,337 parturitions) from 2005 to 2022. Estimates of heritability and repeatability were 0.12 ± 0.024 and 0.24 ± 0.018. The estimates of proportion of phenotypic variance were 0.13 ± 0.019 and 0.02 ± 0.011 for permanent and maternal permanent environmental components, respectively. Estimates of heritability for maximum lifetime temperament score and proportions of temperament scores >1 were 0.18 ± 0.07 and 0.13 ± 0.072. Within cycles (generations), 2-yr-old cows had lower temperament score means than cows in most other age categories. There were low to moderate positive estimates of unadjusted correlation coefficients (r = 0.22 to 0.29; P < 0.05) of unadjusted temperament score with temperament measured on the same females when they were 8 mo old. There were low to moderate positive estimates of correlation coefficients (r = 0.09 to 0.37; P < 0.05) of unadjusted temperament score with calving rate, weaning rate, weaning weight per cow exposed, and weaning weight per 454 kg cow weight at weaning. Cows with the lowest temperament score had lower (P < 0.05) calving and weaning rate than cows in other temperament categories. Within 3 of 5 cycles, cows with the lowest temperament score (totally docile) had lower (P < 0.05) weaning weight per cow exposed than cows in other temperament categories. There were 2 SNP on BTA 4 associated with maximum lifetime temperament score (FDR < 0.05). The non-genetic influence of a cow's mother was documented in her own temperament measured at the time of calving; this may be a consequence of learned behavior. Less aggressiveness displayed by cows at the time of calving may be accompanied by lower reproductive and maternal performance.