A Cox proportional-hazards model with time-dependent covariates to evaluate the relationship between body-condition score and the risks of first insemination and pregnancy in a high-producing dairy herd

The objective of this study was to determine the relationship between body- condition score and postpartum reproductive efficiency in dairy cattle. Dat a on body-condition score, reproduction, diseases, and production from 1404 lactations of 639 cows, calving between January 1984 and November 1996 on a commercial farm, were used. The cox proportional-hazards model with time- dependent covariates was used to qualify the relationship between body-cond ition score on a scale of 1 to 5 and risks of first insemination and pregna ncy. Cows with body condition at calving <3 had lower first-insemination ri sks. Loss of body-condition score between calving and 45 days after calving was associated with increased days open and days-to-first insemination. Co ws with body-condition scores <2 after Day 45 and before first insemination were less likely to be inseminated and become pregnant compared with cows that had higher body condition. Milk yield, mastitis, lameness, milk fever and genital infection were associated with a reduction in reproductive effi ciency. The results indicated that loss of body-condition and actual body-c ondition scores before conception or first insemination or both can be used as a prognosis for days open and days-to-first insemination in dairy herds . (C) 1998 Elsevier Science B.V. All rights reserved.