Analysis of Risk Factors for Dystocia in a Turkish Holstein Herd

The aim of this study was to investigate the effects of calf birth weight, sex of calf, dam weight, parity of dam, age at first calving, gestation length, season and year of calving on dystocia in a Turkish Holstein herd. The data were collected from the Holstein herd of the research farm of the Agricultural Faculty of Ege University. A total number of 687 calvings (single births) from January 2005 through May 2010 were investigated in the study. The results of the preliminary analysis showed that dystocia was much more prevalent in primiparous cows (41.9% dystocia) compared with multiparous cows (5.1% for second parity and 4.4% for third and greater parity cows). Therefore, the data set was divided into two parts for analyzing dystocia in primiparous (236 first calvings) and multiparous (451 sec and later calvings) cows separately. Binary logistic regression analysis was used to determine the factors affecting dystocia. Variables which had a p-value of ≤0.15 in univariate logistic regression analysis were included in the multivariate analysis. In this stage, backward stepwise logistic regression analysis was carried out and variables which had a p-value of ≥0.10 were removed from the model. For primiparous cows, variables in the univariate analyses with a p-value ≤0.15 were sex of calf, birth weight class, dam weight class, ratio of calf birth weight to dam weight class, gestation length class and year of calving. Of these 6 variables included in the multivariate logistic regression analysis, birth weight class, gestation length class and year of calving remained in the model (p<0.05). The risk of dystocia increased with increasing birth weight in first parity cows. Compared to the reference category (birth weight class of ≤35 kg), the risk of dystocia for calves with birth weight classes of 35.1-40.0, 40.1-45.0 and ≥45.1 kg were 1.96, 4.53 and 5.29 times higher, respectively. Heifers with shorter gestation lengths had a lower risk of dystocia. Heifers with gestation lengths of 271-280 days had a 74% lower risk for dystocia compared to heifers with gestation lengths of ≥281 days. For multiparous cows, factors in the univariate analyses with a p-value of ≤0.15 were sex of calf and year of calving. None of these factors was found to have a significant effect (p>0.10) on dystocia in multivariate logistic regression analysis for multiparous cows.