Ercanbrack S K, Knight A D
U.S. Department of Agriculture, Dubois, ID 83423, USA.
J Anim Sci. 1998 May;76(5):1311-25. doi: 10.2527/1998.7651311x.
To investigate the effectiveness of four selection protocols for improving reproduction in sheep, we evaluated nine selection lines and two random-bred control lines for lamb and wool production. Results were based on 25,026 dam and 30,628 lamb records from Rambouillet (R), Targhee (T), Columbia (C), and Polypay (P) sheep collected from 1976 through 1988. Phenotypic trends over years were positive (P < .01) for most reproductive traits, body weight, wool grade (coarser grades), and lamb weaning weight in nearly all selected lines. Small positive trends for both random-bred control lines indicated there were improvements in management and(or) environment during the period. Small but significant phenotypic declines in fleece weights occurred in most lines, including controls. Substantial genetic gains (P < .01) in litter weight weaned (120 d), net reproductive rate (lambs weaned divided by ewes mated), prolificacy, body weight, and weaning weight were made in nearly all selected lines. There were also small but significant improvements in milk score in most lines. There were significant genetic declines and improvements in fleece weights; however, the average genetic change in fleece weight for lines selected for litter weight weaned was negligible. Genetic improvement in litter weight weaned was attributed approximately 37% to prolificacy, 27% to percentage of lambs weaned, 17% to lamb weaning weight, 12% to fertility, and 7% to ewe viability from breeding to lambing. On average, selection based on independent culling levels (litter weight weaned plus yearling body weight), yearling body weight, or early puberty was only 85, 67, or 59%, respectively, as effective as that based solely on litter weight weaned for improving litter weight weaned. The net value of the average (over all breeds) annual increase in production per ewe resulting from selection for litter weight weaned accumulated over 12 yr to an estimated $11.40 and $21.51 annually for genetic and phenotypic increases, respectively.
为了研究四种选择方案对提高绵羊繁殖性能的有效性，我们评估了九个选择品系和两个随机繁殖对照品系的羔羊和羊毛生产情况。结果基于1976年至1988年收集的兰布耶（R）、塔吉（T）、哥伦比亚（C）和波吕佩（P）绵羊的25,026条母羊记录和30,628条羔羊记录。在几乎所有选择品系中，多年来大多数繁殖性状、体重、羊毛等级（较粗等级）和羔羊断奶体重的表型趋势均为正向（P <.01）。两个随机繁殖对照品系均呈现小幅度的正向趋势，表明在此期间管理和（或）环境有所改善。在大多数品系（包括对照品系）中，羊毛重量出现了小幅度但显著的表型下降。几乎所有选择品系在断奶窝重（120天）、净繁殖率（断奶羔羊数除以配种母羊数）、繁殖力、体重和断奶体重方面都取得了显著的遗传进展（P <.01）。大多数品系的乳汁评分也有小幅度但显著的提高。羊毛重量存在显著的遗传下降和提高；然而，选择断奶窝重的品系中羊毛重量的平均遗传变化可忽略不计。断奶窝重的遗传改良约37%归因于繁殖力，27%归因于断奶羔羊百分比，17%归因于羔羊断奶体重，12%归因于繁殖力，7%归因于母羊从配种到产羔的存活率。平均而言，基于独立淘汰水平（断奶窝重加周岁体重）、周岁体重或早期青春期的选择，对于提高断奶窝重的效果分别仅为仅基于断奶窝重选择的85%、67%或59%。因选择断奶窝重而导致的每只母羊年平均产量增加的净值（在所有品种中），在12年中累计，遗传增加和表型增加分别估计为每年11.40美元和21.51美元。
