Beef-on-Dairy breeding in Danish Jersey cattle: Effects of sire breed on dystocia and early culling.

A beef-on-dairy breeding strategy can improve beef value output from dairy herds but may simultaneously increase the risk of dystocia and early culling. Using data from 403,133 calvings in Denmark and 109 completed questionnaires returned by members of the Danish Jersey federation, we evaluated the risk of dystocia and subsequently early culling in purebred Jersey dams inseminated with semen of either Jersey, Aberdeen Angus, or Danish Blue sires. The study was designed as a retrospective cohort and cross-sectional study. The total prevalence of dystocia across all parities was 0.82% for J×J, 2.30 for A×J, and 2.97% for B×J. Relative to Jersey sires, the odds of dystocia increased in the order Jersey, Angus, and Danish Blue, with ORs of 2.58 (95% CI = [2.01; 3.31]) for Angus sires and 3.66 (95% CI = [3.09; 4.32] for Danish Blue sires. The dystocia rate was highest in heifers, followed by cows in their third or later parity, and lowest in second-parity cows. Male calves were associated with a higher risk of dystocia than female calves (OR = 2.21, CI 95% = [1.95; 2.50]). The risk of developing dystocia decreased with increasing maternal calving ease and birth indexes. The risk of early culling was correlated to sire breed and parity. Cows inseminated with Aberdeen Angus and Danish Blue semen had an elevated risk of early culling: OR = 1.22; 95% CI = [1.06; 1.41] and OR = 1.34, 95% CI = [1.22; 1.48], respectively. Compared with first-parity dams, parity 2 dams had a lower risk of early culling (OR = 0.70, 95% CI = [0.67; 0.74]), whereas dams in parity ≥3 had an increased risk (OR = 1.34, 95% CI = [1.29; 1.40]). An increase in Nordic Total Merit (NTM) was associated with a slightly reduced risk of early culling (OR = 0.993, 95% CI = [0.991; 0.995]). These findings show that sire breed, calf sex as well as dam parity and maternal calving ease and birth indexes, should be considered when employing a beef-on-dairy breeding strategy in the Jersey breed to reduce the risk of dystocia and early culling. The results of the farmer questionnaire indicated that the beef-on-dairy strategy is widely implemented and mainly applied to multiparous cows with low NTM.