Evaluation of the effect of twin births on the perinatal calf mortality and productive performance of Holstein dairy cows

Calving records from the Animal Breeding Center of Iran collected from January 1993 to December 2007 and comprising 1 163 594 Holstein calving events from 2 552 herds were used to evaluate reported perinatal calf mortality, 305-d milk yield, 305-d fat yield of milk and 305-d fat percentage of milk in singleand twin-births. A logistic regression model was constructed to analyze calf mortality between singletons and twins. Also statistical analyses of 305-d milk yield, 305-d fat yield of milk and 305-d fat percentage of milk were performed using the general linear models procedure. Greater odds of calf mortality existed for calves born from primiparous cows than from multiparous cows (P<0.001) and for calves born as twins than singletons. The odds of calf mortality increased over years from 4.2 % in calving year Y1 (1993-1997) to 5.1 % in calving year Y3 (2003-2007) (odds ratio [OR] = 1.14; P<0.001). The odds of calf mortality was greater after twin births, with 16.7 % of the twin calving events reporting calves as dead compared to 5.2 % for singleton births (OR=5.62; P<0.001). For same-sex twin pairs, the odds of calf mortality was greater (P<0.01; OR=1.72) for male than for female twin pairs. Also, twin-calved cows had greater 305-d milk production, fat yield and fat percentage of milk than single-calved cows (P<0.05). In general, development of practical management strategies to cope with the negative effects associated with twinning on dairies is critical, especially if the trend toward increased twinning in the dairy cattle population continues.