Risk factors and rates of perinatal and postnatal mortality in cattle in Switzerland

There have been many studies on perinatal and postnatal mortality in calves, but most are limited to small numbers of breeds or herds. The goal of this study was to determine the perinatal (first 24 h) and postnatal mortality rates during the first four months in 22 breeds and cross-breeds commonly occurring in Switzerland and to identify possible risk factors. From 2005 to 2007, 2,122,184 calvings were analysed, which yielded an overall perinatal mortality rate of 2.4%. There was a significant yearly increase in the mortality rate. The postnatal mortality rates from days 2 to 7, 8 to 28 and 29 to 120 were 0.5%, 1.3% and 0.7%, respectively. Dystocia was associated with a relative risk of perinatal mortality of 12.2, and significantly affected the postnatal mortality rates in all time periods investigated. The overall dystocia rate associated with bull calves was more than twice that of heifers, but there was no sex-related difference in Dexter, Hereford, Highland cattle, Hinterwälder, Jersey und Normande breeds. There were significant correlations between the mean birth weights of the different breeds and the dystocia rate (r = 0.6), and between the mean difference in male and female birth weights of the different breeds and the dystocia rate (r = 0.6). Perinatal mortality was also significantly affected by age of dam, gestation length, sex and weight of calf, season and herd size. Breed had a significant effect on perinatal and postnatal mortality rates, and there were significant interactions between breed and other risk factors of mortality. The identification of breed-specific risk factors of perinatal and postnatal mortality could help to develop strategies to alleviate the problem.