Guerra-Martinez P, Dickerson G E, Anderson G B, Green R D
University of Nebraska, Lincoln 68583-0908.
J Anim Sci. 1990 Dec;68(12):4039-50. doi: 10.2527/1990.68124039x.
Effects of twinning on efficiency of beef production were estimated from results of bilateral transfer of two Angus x Hereford (AxH) embryos into each of 241 heifers and 84 cows (H, A, HxA or Holstein x 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 less than .05), and tended to be less (P greater than .05) for T than S in H. More placentas were retained (P less than .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 less than .05), but total calf mortality was slightly higher (P greater than .05). Abortions were 4% in H only. Twinning females lost maternal weight during late gestation (P less than .05) when crowding limited voluntary feed intake, while fetal requirements were 60% higher (P less than .01). Twins increased milk output 25% (P less than .05), but 11% higher feed intake maintained cow weight during lactation. Twinning reduced birth weight 13% and weaning weight 17% (P less than .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 less than .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.
通过在4年时间里将两枚安格斯×赫里福德（AxH）胚胎双侧移植到241头小母牛和84头母牛（赫里福德、安格斯、赫里福德×安格斯或荷斯坦×赫里福德）体内的结果，评估了孪生对牛肉生产效率的影响。犊牛在180日龄时断奶，1977年在饲养场育肥220天，1978年至1980年先在牧场饲养170天，然后在饲养场饲养140天。将胎次、孪生情况和犊牛性别作为母本年份-品种内的协变量进行评估。妊娠45至60天时，小母牛的妊娠率为68%，母牛为74%，单胎（S）出生率为40%，双胎（T）出生率为60%。小母牛的难产率为28%，母牛为10%（P<0.05），小母牛中双胎的难产率比单胎低（P>0.05）。在小母牛（35%对12%）和母牛（24%对4%）中，双胎保留胎盘的比例均高于单胎（P<0.05）。双胎妊娠平均缩短3天，随后的产犊间隔延长13天（P<0.05），但犊牛总死亡率略高（P>0.05）。仅小母牛中有4%发生流产。当拥挤限制了自愿采食量时，双胎母牛在妊娠后期体重减轻（P<0.05），而胎儿需求高60%（P<0.01）。双胎使产奶量增加25%（P<0.05），但采食量增加11%以维持母牛在泌乳期的体重。孪生使出生体重降低13%，断奶体重降低17%（P<0.05），但由于饲养场的补偿性增重，400日龄时的饲养场体重仅降低9%。双胎在断奶后170天的牧场饲养期内比单胎生长快18%，但在饲养场中生长慢5%，490日龄时体重轻8%（P<0.05）。假设双胎的兽医和劳动力成本高40%，则无论是在断奶时还是400日龄时销售，每单位年龄恒定产值的估计综合牛群成本，双胎生产比单胎生产低约24%。
