Effects of twinning on lactation and days open in Holsteins.

Effects of twinning on lactation and days open in Holsteins were studied from calving records compiled by member surveys of Eastern Artificial Insemination Cooperative. Records of cows with 305-day mature-equivalent records from the Northeast Dairy Records Processing Laboratory were grouped according to whether the twin calving was associated with dystocia. Records of each cow that had a twin calving were paired with records of a single-calving control herdmate. In the twin group of 175 cows associated with dystocia, twin pregnancy had no effect on production; milk and fat production in the lactation initiated by twinning was depressed (137 kg and 7 kg) although not significantly; and days open following twin calving was increased. In the twinning group of 367 cows with no dystocia at twinning, milk and fat production were depressed by 285 kg and 14 kg in the lactation initiated by the twinning. Days open after twinning were increased by about 22 days. These results indicate a negative economic effect of twinning on lactation performance in Holstein cattle. Increased rates of twinning via selection or artificial induction of twinning dairy cattle appear not to be desirable.