EFFECTS OF TWINNING ON DYSTOCIA, CALF SURVIVAL, CALF GROWTH, CARCASS TRAITS, AND COW PRODUCTIVITY

This paper reports results from a long-term experiment with a primary objective to increase twinning rate in cattle at the Roman L. Hruska U .S. Meat Animal Research Center. Survival of singles was 13% higher (P < .01) than that of twins at birth, and the difference in survival in favor of singles was of similar magnitude at 72 h (12.9%, P < .01), 1 50 d (14.8%, P < .01), and 200 d (15.2%, P < .01). Survival of calves with no dystocia was higher than survival of calves with dystocia: 8.6 % (P < .01) at birth, 10.8% (P < .01) at 72 h, 12% (P < .01) at 150 d, and 12.2% (P < .01) at 200 d. The effect of dystocia on survival was greater (P < .01) in twins than in singles at birth and at 72 h. Least squares means for dystocia were 20.4% in singles compared with 42.2% in twins. Most of the dystocia in singles resulted from a traction req uirement (84.7%) of normal presentations, whereas most of the dystocia in twins (77.8%) resulted from malpresentations, with 59.2% of the ma lpresentations accompanied with a requirement for traction. Survival i n singles ranged from 10.7% to 15.3% greater than in twins at differen t ages when there was no requirement for assistance in either singles or twins. Calves born as singles were 8.8 kg heavier(P < .01) at birth and 28 kg heavier(P < .01) at 200 d than calves born and reared as tw ins. Calf weight produced per cow calving was 53.1%, 54.7%, and 58.4% greater (P < .01) at birth, 150 d, and 200 d, respectively, in cows pr oducing twins than in cows producing singles. Cows producing twins had 65.2% more (P < .01) live calves at 200 d than cows producing singles . Single male calves gained 74 g more per day than twin males from bir th to 200 d, 45 g more (P < .01) per day from 200 d to slaughter and 5 7 g more (P < .01) per day from birth to slaughter. Differences betwee n twin and single males in carcass traits were small. A sample of stee rs from the Twinning Project gained significantly faster and produced significantly more desirable carcasses than a sample of steers from a high performance reference population. Freemartins did not differ (P > .05) from normal females in growth traits, but freemartins had higher (P < .05) scores for marbling with a higher percentage (P < .05) of U SDA Choice or better quality grade carcasses and lower estimated perce ntage retail product.