Embryo-transfer twinning and performance efficiency in beef production1

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Abstract
Effects of twinning on efficiency of beef production were estimated from results of bilateral transfer of two Angus × Hereford (A×H) embryos into each of 241 heifers and 84 cows (H, A, H×A or Holstein × H) over 4 yr. Calves were weaned at 180 d and fed either 220 d in a feedlot (1977) or 170 d on forage and 140 d in a feedlot (1978 to 1980). Effects of parity, twinning and sex of calf were estimated as covariates within year-breed of dam. Pregnancy at 45 to 60 d of gestation was 68% in heifers (H) and 74% in cows (C), with 40% single (S) and 60% twin (T) births. Dystocia was 28% in H vs 10% in C (P < .05), and tended to be less (P > .05) for T than S in H. More placentas were retained (P < .05) for T than for S in both H (35 vs 12%) and C (24 vs 4%). Twin gestations averaged 3 d shorter and subsequent calving intervals 13 d longer (P <.05), but total calf mortality was slightly higher (P > .05). Abortions were 4% in H only. Twinning females lost maternal weight during late gestation (P <.05) when crowding limited voluntary feed intake, while fetal requirements were 60% higher (P < .01). Twins increased milk output 25% (P < .05), but 11% higher feed intake maintained cow weight during lactation. Twinning reduced birth weight 13% and weaning weight 17% (P < .05), but 400-d feedlot weight only 9% because of compensating feedlot gain. Twins gained 18% faster than S during postweaning 170-d forage feeding, but 5% slower in feedlot to 8% lighter 490-d weight (P < .05). Assuming 40% higher veterinary and labor costs for twins, estimated integrated herd costs per unit of age-constant output value would be lower for T than for S production by about 24% for marketing either at weaning or at 400 d.

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