The relationships among sire's predicted transmitting ability for daughter pregnancy rate and cow conception rate and daughter's reproductive performance in Canadian Holstein cows

The objectives of this study were to (1) characterize the variability for sire's predicted transmitting ability (PTA) for daughter's pregnancy rate (DPR) and cow conception rate (CCR), (2) determine the relationships among sire's PTA for DPR, sire's PTA for CCR, daughter's parity, and daughter's 305-d mature-equivalent (ME) milk production, and (3) evaluate the associations among sire's PTA for DPR and CCR and daughter's reproductive performance [pregnancy to first artificial insemination (P/AI), pregnancy by 150 d in milk (PR150) and pregnancy loss (PL) after first AI] in Canadian Holstein cows. The data were obtained from 822 lactating Holstein cows from 10 commercial dairy herds located in Alberta. Overall mean (range) for sire's PTA for DPR and CCR was -0.09 (-9.6 to 8.2) and -0.05 (-9.9 to 7.4), respectively. Sire's PTA for DPR was strongly and positively associated with sire's PTA for CCR (r = 0.89; P < 0.01). Sire's PTA for DPR and CCR were weakly and negatively associated with parity (r = -0.15 and -0.17, respectively; P < 0.01); however, the amount of phenotypic variation in sire's PTA for DPR and CCR explainable by parity was small (coefficient of determination; R² = 0.02). The daughter's 305-d ME milk production tended to be weakly but positively associated with sire's PTA for DPR (r = 0.06; P = 0.07) and CCR (r = 0.06; P = 0.10); however, the amount of phenotypic variation in daughter's 305-d ME milk production explainable by changes in sire's PTA for DPR or CCR was small (R² = 0.004 and 0.003, respectively). Overall P/AI, PR150 and PL were 38, 65 and 12%, respectively. Sire's PTA for DPR tended to be associated with P/AI (P = 0.08) but was significantly associated with PR150 (P = 0.03). For every unit increase in sire's PTA for DPR, the estimated probabilities for P/AI and PR150 increased by 6.2 and 7.5%, respectively. Sire's PTA for CCR was not associated with P/AI or PR150. Neither sire's PTA for DPR nor CCR were associated with PL. In summary, sire's PTA for DPR and CCR were highly variable and positively correlated. Sire's PTA for DPR was associated with daughter's P/AI and PR150, but sire's PTA for CCR was not associated with any of the measured reproductive outcomes. Therefore, selecting sires with high PTA for DPR has the potential to improve the reproductive efficiency of Canadian dairy herds.