Lasslo L L, Bradford G E, Torell D T, Kennedy B W
J Anim Sci. 1985 Aug;61(2):376-86. doi: 10.2527/jas1985.612376x.
In 1961, selection for 120-d weight was initiated in two flocks from a common base population of grade Targhee sheep. At Davis, sheep were maintained on a good plane of nutrition, on irrigated pasture or in drylot. At Hopland, sheep grazed annual grassland range, with supplementary feeding only at mating and lambing. Selected (DW) and control (DC) lines were maintained at Davis from 1961 through 1977. A selected (HW) line, replicate control (HC1 and HC2) lines and a line (DH) mated to the Davis DW rams were maintained at Hopland from 1961 through 1980, with the exception that HC2 was terminated in 1977. Multiplicative factors were used to adjust weights for effects of age of dam, sex and type of birth and rearing. Response to selection was estimated as the difference between selected and control line linear regression coefficients of adjusted line means on year. The Hopland replicate controls did not differ significantly from each other (HC1 - HC2 = .004 +/- .056 kg/yr), and the control line data were pooled (HC). The overall control line mean 120-d weights on a female, single, mature-dam basis were 33.2 and 30.4 kg at Davis and Hopland, respectively. Direct response was greater at Davis than at Hopland: DW - DC = .524 +/- .073 kg/yr (P less than .001); HW - HC = .151 +/- .034 kg/yr (P less than .001). Corresponding realized heritabilities were .17 and .06. Direct response for the DH line was DH - HC = .226 +/- .036 (P less than .001); realized heritability was .08. Response in the DH line was greater (P less than .05) than that in the HW line: HW - DH = -.075 +/- .037 kg/yr. This indicates that: (1) genetic improvement made on a higher plane of nutrition was expressed, but to a lesser degree, under range conditions and (2) selection under better feed conditions resulted in at least as much improvement in growth rate in a range environment as did selection under range conditions.
1961年，从塔吉羊杂种基础群体中选出两个羊群，开始进行120日龄体重的选育。在戴维斯，羊群饲养在营养水平良好的灌溉牧场或干栏式畜舍中。在霍普兰德，羊群在一年生草地牧场放牧，仅在配种和产羔时进行补饲。从1961年到1977年，在戴维斯维持选育系（DW）和对照系（DC）。从1961年到1980年，在霍普兰德维持一个选育系（HW）、重复对照系（HC1和HC2）以及一个与戴维斯DW系公羊交配的系（DH），不过HC2在1977年终止。使用乘性因子来调整体重，以消除母羊年龄、性别以及出生和饲养类型的影响。选择反应估计为选育系和对照系调整后品系均值对年份的线性回归系数之差。霍普兰德的重复对照系之间差异不显著（HC1 - HC2 = 0.004 ± 0.056千克/年），因此将对照系数据合并（HC）。以雌性、单胎、成年母羊为基础，戴维斯和霍普兰德对照系的120日龄体重总体均值分别为33.2千克和30.4千克。戴维斯的直接选择反应大于霍普兰德：DW - DC = 0.524 ± 0.073千克/年（P < 0.001）；HW - HC = 0.151 ± 0.034千克/年（P < 0.001）。相应的实现遗传力分别为0.17和0.06。DH系的直接选择反应为DH - HC = 0.226 ± 0.036（P < 0.001）；实现遗传力为0.08。DH系的选择反应大于HW系（P < 0.05）：HW - DH = -0.075 ± 0.037千克/年。这表明：（1）在较高营养水平上实现的遗传改良在放牧条件下也能表现出来，但程度较小；（2）在较好饲养条件下的选择在放牧环境中对生长速度的提高至少与在放牧条件下的选择相同。
