Cow attributes, herd management, and reproductive history events associated with abortion in cow-calf herds from Western Canada.

The primary objective of this study was to identify herd management and cow characteristics that are associated with abortion in cow-calf herds in Western Canada. Reproductive events were closely monitored in 29,713 cows in 203 herds from the beginning of the breeding season in 2001 through the calving season in 2002. Herd management and cow-level risk factors such as age, body condition score, and previous reproductive history were measured through a series of herd visits by project personnel and detailed individual animal records maintained by the herd owner. Pregnancy status was assessed in fall of 2001 by the herd veterinarian. Cows most likely to abort were replacement heifers, cows that were more than 10 years of age, cows with a body condition score of less than or equal to or 5 of 9 at pregnancy testing, or with twin pregnancies. Cows vaccinated for bovine viral diarrhea virus and infectious bovine rhinotracheitis and bred on community pastures were less likely to abort than cows from community pastures that were not vaccinated. Cows bred on community pastures that were not vaccinated were also more likely to abort than cows that were not on community pastures regardless of vaccination status. Adverse calving-associated events such as severe dystocia, problems such as uterine prolapse or retained placentas, abortion or calf death within 1 hour of birth were also associated with an increased risk of abortion the subsequent calving season after accounting for all other factors.