Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/1995
Publication Date: N/A
Interpretive Summary: Calf weight produced at 200 d per cow calving can be increased by 58.4% in cows producing twins relative to cows producing singles. However, the requirement for assistance at calving was more than twice as great in twins than in singles (42.2% vs.20.4%) and calf survival to 200 d was 15.2% greater in singles than in twins. Thus, greater dystocia and lower calf survival are major constraints to twinning technology. Differences betwee twins and singles in rate of gain, although significant, were small (57 g/day) from birth to slaughter. This population that has been selected intensively for twinning rate is equal or superior to a high performance population for growth and carcass traits. Thus, twinning technology could be implemented using germplasm from this population without compromise of growth rate and carcass merit.
Technical Abstract: 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 higher (P < .01) than twins at birth, 72 h, 150 d, and 200 d. Survival of calves with no dystocia was higher than survival of calves with dystocia. 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 requirement (84.7%) of normal presentations, whereas most of the dystocia in twins (77.8%) resulted from malpresentations. 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 twins. Calf weight produced per cow calving was 53.1%, 54.7%, and 58.4% greater (P < .01), respectively, at birth, 150 d, and 200 d in cows producing 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 57 g more (P < .01) per day from birth to slaughter than twin males. Differences between twin and single males in carcass traits were small. A sample of steers from the Twinning Project gained significantly faster and produced significantly more desirable carcasses than a sample of steers from a high performance reference population. Steers from the Twinning Project did not differ (P > .05) from the reference population in gain efficiency evaluated to time constant (228 d), gain constant (255-575 kg), or marbling score constant (small) end points.