SUMMARY
The objective of this study was to assess various risk factors affecting fetal losses in high-yielding Holstein cows in a hot environment. In a retrospective observational study, 14,384 records from Holstein cows from a large highly technified dairy herd in northern Mexico were used. Logistic multivariate multiple-group response model indicated that fetal losses between 43 and 260 days of pregnancy were 23.8%. Dry periods >60 d were associated (p<0.05) with 0.8 (confidence interval CI=0.8–0.9) times lower incidence of fetal losses compared to cows with dry periods <60 d. Cows with body condition score (BCS) >3 at calving and 15 days postpartum had about half the risk of suffering fetal losses than cows with BCS <3.0. Cows with peak milk yield >38 kg were 5.5 times more likely to have a fetal loss than cows with peak milk yield <38 kg (36.9 vs. 9.6%; p<0.01). The risk of fetal loss increased with 305-d milk yield >9,000 kg (OR=2.1) compared with cows with milk yield <9,000 kg. Retained placenta was (p<0.05) associated with 1.2 (CI=1.1–1.4) times higher fetal losses than cows without this reproductive disorder. Cows suffering premature parturition had 1.2 (CI=1.0–1.4) greater (p<0.05) risk of suffering fetal losses than cows with normal parturition. Cows with twin pregnancies had significantly increased chances of losing their fetuses than cows with a single fetus (31.1 vs. 15.9 p<0.01). A bimodal distribution of fetal losses was observed with peaks around 50 and 220 days of pregnancy. It was concluded that in this particular hot environment fetal losses were associated with high milk yield, low body energy reserves at calving, reduced dry periods, occurrence of retained placenta, twin pregnancies and premature calving.