Lasslo L L, Bradford G E, Torell D T, Kennedy B W
J Anim Sci. 1985 Aug;61(2):387-97. doi: 10.2527/jas1985.612387x.
Targhee sheep were selected for 120-d weight under irrigated pasture-drylot conditions at Davis (DW) and under range conditions at Hopland (HW). Unselected control lines were maintained in both environments (DC, HC1 and HC2). At Hopland, a line (DH) was maintained in which ewes were mated to Davis (DW) rams. Selection for 120-d weight was successful in both environments, with more improvement made in the drylot environment. The genetic improvement made in the drylot environment was expressed, although to a lesser degree, under range conditions. Correlated responses were analyzed. Birth weight increased significantly in all three selected lines; the increase was less in line DH than in the other two lines. In all selected lines, weights of ewes of all ages at mating increased significantly compared with their respective controls. Proportion of ewes lambing decreased (P less than .05) in line DH; the trend was negative but nonsignificant in line DW. Differences in litter size between lines within location were not significant. Lamb survival to weaning decreased in lines DW (P less than .05) and DH (P less than .01), compared with their respective controls; and the trend in HW was negative but nonsignificant. Fertility and survival data indicated that, under range conditions, the line selected under drylot conditions (DH) was less fit than the line selected under range conditions (HW). As a result of the decreases in lamb survival and fertility, none of the selected lines produced more total lamb weight weaned per ewe than the controls, in spite of the significant direct response to selection. Mature ewes of lines DH and DW produced less total lamb weight weaned per ewe (P less than .001 and P less than .05) than their respective controls. The results indicate that while single trait selection for growth rate to weaning results in heavier lambs, it does not increase and may decrease total lamb production per ewe.
在戴维斯地区的灌溉牧场-干圈舍条件下（DW）以及霍普兰德地区的放牧条件下（HW），对塔尔基羊进行了120日龄体重的选育。在这两种环境中都维持了未选育的对照品系（DC、HC1和HC2）。在霍普兰德地区，维持了一个品系（DH），其中母羊与戴维斯地区（DW）的公羊交配。对120日龄体重的选育在两种环境中均取得成功，在干圈舍环境中取得了更大的进展。尽管程度较小，但在放牧条件下，干圈舍环境中实现的遗传进展仍有所体现。对相关反应进行了分析。所有三个选育品系的出生体重均显著增加；DH品系的增加幅度小于其他两个品系。在所有选育品系中，与各自的对照相比，配种时所有年龄母羊的体重均显著增加。DH品系中产羔母羊的比例下降（P<0.05）；DW品系的趋势为负，但不显著。同一地点内各品系之间的产仔数差异不显著。与各自的对照相比，DW品系（P<0.05）和DH品系（P<0.01）的羔羊断奶存活率下降；HW品系的趋势为负，但不显著。繁殖力和存活率数据表明，在放牧条件下，在干圈舍条件下选育的品系（DH）比在放牧条件下选育的品系（HW）适应性更差。由于羔羊存活率和繁殖力下降，尽管对选育有显著的直接反应，但没有一个选育品系每只母羊断奶时的总羔羊体重超过对照。DH品系和DW品系的成年母羊每只母羊断奶时的总羔羊体重低于各自的对照（P<0.001和P<0.05）。结果表明，虽然对断奶生长率进行单性状选育会使羔羊体重增加，但并不会增加甚至可能会减少每只母羊的总羔羊产量。
