Twinning in Cattle: 111. Effects of Twinning on Dystocia, Reproductive Traits, Calf Survival, Calf Growth and Cow Productivity

An evaluation of natuml twinning in beef cattle revealed that cows birthing twins had shorter (P c .Ol) gestation lengths, more (P e .Ol) retained placentas, more (P < .01) dystocia, more (P e .01) days to e m s , lower (P e .01) conception rates and more (P < .01) days to pregnancy than cows birthing singles. Days to estrus, conception rate and days to pregnancy were not affected by number of calves reared (1 vs 2) in cows birthing twins. Survival at birth was greater (P e .01) for singlethan for twin-born calves, but twins and singles did not differ (P > .Os) in postnatal survival. When dystocia was experienced, calf survival at birth was 95% vs 73% for singles vs twins compared with 99% vs 92% when no dystocia was experienced. Calves born twins were lighter (P e .01) at birth, 100 d and 200 d, but twins and singles did not differ in postweaning gains. Total calf weights at 100 d per cow calving were 12% greater (P c .01) in cows bixthing twins vs singles when twin calves reared by foster dams were! excluded. The potential increase in cow productivity for total calf weight at 100 d is 40% if calf survival rates of twins with dystocia relative to survival rates of twins without dystocia were comparable to swival rates of singles with and without dystocia, and if cows birthing twins were fed and managed to obtain conception rates equal to those of cows birthing singles. Identification of cows gestating twins to provide for their higher prepartum nutritive requirements and calving assistance at parturition is necessary to make twinning in cattle an economically viable technology. (