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We examined the association of some risk factors with subfertility in Holstein cows under Egypt's subtropical climate. Lactations (n = 1832) from a high-yielding (305-d milk yield ≈ 10,000 kg) herd were enrolled. Only 10% of cows became pregnant to first AI, and 21.2% were pregnant by 120 days in milk, DIM (PREG120). The likelihood of PREG120 decreased significantly in high-yielding cows, after spring and summer calvings, and when the first AI occurred after 65 DIM. For cows with lameness, mastitis, or reproductive problems prior to pregnancy, the odds of PREG120 decreased by 38%, 68%, and 36%, respectively. Increased milk production (OR: 1.54 for moderate, and 2.21 for high producers), summer calving (OR: 2.18), and affection with lameness (OR: 1.71), mastitis (OR: 2.57), or reproductive disorders (OR: 1.29) increased the risk of repeat breeding compared to low-producing, winter calving, and non-affected cow, respectively. Unadjusted mean number of services per conception was 4.29. Cows in the moderate- and high-milk groups, cows who calved in seasons other than fall, and those affected with lameness or mastitis all required more AI for pregnancy. In conclusion, fertility of cows in the herd under investigation was suboptimal. To sustain fertility in subtropical conditions, cows should be shielded during hot months, bred earlier than 65 DIM, and cows suffering from dystocia, retained placenta, metritis, lameness, or mastitis should be properly handled to minimize their detrimental impact on subsequent fertility. Also, breeding methods should be tailored for high-producing animals with special consideration paid to their condition.
Sahwan et al. (Mon,) studied this question.