The effects of time of disease occurrence, milk yield, and body condition on fertility of dairy cows

The associations between occurrence of diseases, milk yield, and body condi tion score on conception risk after first artificial insemination (AI) were analyzed in an observational study on a convenience sample of 43 farms par ticipating in a herd health program. Data were taken from 9369 lactations, from 4382 cows inseminated between 20 and 180 d in milk from 1990 to 1996. Two logistic regression models, one containing data from all lactations and a subset containing data from 1762 lactations with body condition scoring, were used to determine pregnancy risk at first Al. The effects of herd dev iation in test-day milk yield, body condition score loss, and milk fat to p rotein ratio changes in early lactation were significant predictors of preg nancy risk, independent of disease; days in milk; farm; and seasonal factor s. Three different methods of disease parameterization (incidence rates, bi nomial classes dependent on the interval in days since last occurrence with respect to Al, and a linear variable weighted for this interval) produced similar results. Metritis, cystic ovarian disease, lameness, and mastitis g ave odds ratios for pregnancy risk ranging from 0.35 to 1.15, largely depen dent on the interval in days from final disease occurrence to first AI. Dis placed abomasum, milk fever, and retained fetal membranes resulted in odds ratios for pregnancy risk of 0.25, 0.85, and 0.55, respectively. These dise ases showed little relationship between fertility and the number of days si nce last occurrence. Results of this study confirm the negative effects of milk yield, body score condition loss, and disease on dairy cow fertility. The effects of some diseases on first service conception were strongly depe ndent on the interval since last disease occurrence. This was especially va lid for clinical mastitis, which has an extremely weak effect on conception if occurring prior to AI and is associated with >50% reduction in pregnanc y risk if occurring in the 3 wk directly after Al.