Snowder G D, Van Vleck L D
USDA, ARS, U.S. Meat Animal Research Center, Clay Center, NE 68933, USA.
J Anim Sci. 2003 Nov;81(11):2704-13. doi: 10.2527/2003.81112704x.
The objectives of this study were to estimate (co)variance components for growth and feed efficiency measures, and to compare selection strategies to improve economic efficiency of gain. Variance components for pre- and postweaning growth, body weight, and measures of feed efficiency were estimated from data collected on 1,047 Targhee lambs over 7 yr. Approximately 21 d after weaning, lambs were group-fed for 4 wk, with ad libitum access to a diet of 37% whole barley grain and 63% pelleted alfalfa hay. Lambs were then individually fed for 6 wk. Lambs were then returned to group feeding for another 4-wk period. The mean feed conversion ratio (gain/intake) for the individual feeding period was 0.11. Mean postweaning ADG for the total 14-wk feeding period was 0.26 kg. (Co)variance components were estimated from single- and two-trait animal models using REML. The selection strategies compared included direct selection, index selection, and restricted index selection. Estimates of (co)variances derived from single- and two-trait models were similar, except for mid-test body weight. Preweaning growth had a low heritability estimate (0.03 +/- 0.04) compared with postweaning growth measures (0.25 to 0.39), but all measures of growth were highly correlated (r2 > 0.98). Heritability estimates of measures of gain efficiency were variable (total feed intake = 0.39; feed conversion ratio = 0.26; residual feed intake = 0.26). Total feed intake was strongly correlated genetically with feed conversion ratio (0.79) and residual feed intake (0.77). The estimate of genetic correlation between feed conversion ratio and residual feed intake was low (0.23). Comparison of selection strategies showed the superiority of index selection (ADG, total feed, body weight) for economic improvement compared with other strategies. Economic response to direct selection for ADG was at least twice that for direct selection for feed conversion ratio or against total feed intake, and that for restricted indices (selecting against residual feed, while holding body weight and/or gain constant). Selection for ADG may be a practical approach for indirectly improving efficiency of gain in lambs.
本研究的目的是估计生长和饲料效率指标的（协）方差分量，并比较不同的选择策略以提高增重的经济效率。从7年期间收集的1047只塔尔基羊的数据中估计断奶前和断奶后生长、体重及饲料效率指标的方差分量。断奶后约21天，羔羊进行4周的群体饲养，自由采食由37%整粒大麦和63%苜蓿颗粒干草组成的日粮。然后羔羊进行6周的个体饲养。之后羔羊再次进行4周的群体饲养。个体饲养期的平均饲料转化率（增重/采食量）为0.11。整个14周饲养期的断奶后平均日增重为0.26千克。使用REML从单性状和双性状动物模型估计（协）方差分量。比较的选择策略包括直接选择、指数选择和限制指数选择。除中期体重外，单性状和双性状模型得出的（协）方差估计值相似。与断奶后生长指标（0.25至0.39）相比，断奶前生长的遗传力估计值较低（0.03±0.04），但所有生长指标均高度相关（r2>0.98）。增重效率指标的遗传力估计值各不相同（总采食量=0.39；饲料转化率=0.26；剩余采食量=0.26）。总采食量与饲料转化率（0.79）和剩余采食量（0.77）在遗传上高度相关。饲料转化率与剩余采食量之间的遗传相关估计值较低（0.23）。选择策略的比较表明，与其他策略相比，指数选择（日增重、总采食量、体重）在经济改良方面具有优势。对日增重进行直接选择的经济反应至少是对饲料转化率进行直接选择或对总采食量进行反向选择以及对限制指数（在保持体重和/或增重不变的情况下对剩余采食量进行反向选择）的两倍。选择日增重可能是间接提高羔羊增重效率的一种实用方法。
