Nwakalor L N, Brinks J S, Richardson G V
J Anim Sci. 1986 Apr;62(4):927-36. doi: 10.2527/jas1986.624927x.
Selection intensity and generation interval were evaluated in a Hereford cattle herd made up of 14 inbred lines and 14 linecross groups corresponding to the lines of inbred sires at the Suan Juan Basin Research Center, Hesperus, Colorado. Selection indexes practiced were calculated in retrospect. Analyses of the records collected from 1946 through 1973 involved weaning weight (WW) and postweaning traits in males and females. Analyses by line were performed for the inbreds, while pooled analyses were done on the inbred and linecross populations. From records of 1,239 calves weaned, age of sire averaged 3.75 yr compared with 4.52 yr for age of dam, showing faster generation turnover for sires than for dams. Generation interval determined as actual age of midparent was 4.13 yr. Selection applied for WW, evaluated as annual selection differentials within inbred lines and then pooled over all lines, averaged .55 standard deviations (sigma)/generation for sires. For females, selection was much less intense. Midparent selection differential amounted to .33 sigma/generation. For sires, pooled standardized selection differentials per generation over all lines during the postweaning gain period were .49 sigma, .46 sigma, .40 sigma, -.20 sigma, -.10 sigma and .69 sigma, respectively, for initial weight, final weight, feed consumed, feed efficiency (FE, unadjusted and adjusted) and average daily gain (ADG). Selection of females for postweaning traits was not intense. Selection index actually practiced in retrospect for sires was: IS = .4461 (WW) - .0092 (FE) + .6126 (ADG). The indexes for dams included WW, 12-mo weight (12W), 18-mo weight (18W), mature spring weight (SPW) and mature fall weight (FAW) and were: for inbred dams, ID = .1824 (WW) - .0284 (12W) + .0736 (18W) - .1097 (SPW) - .1097 (FAW); for linecross dams, ID = .2693 (WW) - .2960 (12W) + .0147 (18W) + .1185 (SPW) - .0354 (FAW). The corresponding index selection differentials were .818, .203 and .209. Sire index selection differentials represent about 79% of the total selection differentials.
在科罗拉多州赫斯珀斯市圣胡安盆地研究中心，对一个由14个近交系和14个杂交组（对应近交系父系）组成的赫里福德牛群进行了选择强度和世代间隔评估。回顾性计算了所采用的选择指数。对1946年至1973年收集的记录进行分析，涉及公母犊牛的断奶体重（WW）和断奶后性状。对近交系进行系内分析，对近交群体和杂交群体进行合并分析。从1239头断奶犊牛的记录来看，父系的平均年龄为3.75岁，而母系的平均年龄为4.52岁，表明父系的世代更替比母系更快。以双亲平均实际年龄确定的世代间隔为4.13年。对WW进行选择，评估为近交系内的年度选择差，然后在所有品系间合并，父系平均为0.55个标准差（σ）/代。对于母系，选择强度要小得多。双亲选择差为0.33σ/代。对于父系，在断奶后增重期，所有品系每代合并的标准化选择差，初始体重、终末体重、采食饲料量、饲料效率（FE，未调整和调整后）和平均日增重（ADG）分别为0.49σ、0.46σ、0.40σ、-0.20σ、-0.10σ和0.69σ。对母系断奶后性状的选择强度不大。回顾性实际应用于父系的选择指数为：IS = 0.4461（WW）- 0.0092（FE）+ 0.6126（ADG）。母系的指数包括WW、12月龄体重（12W）、18月龄体重（18W）、成年春季体重（SPW）和成年秋季体重（FAW），对于近交系母系，ID = 0.1824（WW）- 0.0284（12W）+ 0.0736（18W）- 0.1097（SPW）- 0.1097（FAW）；对于杂交系母系，ID = 0.2693（WW）- 0.2960（12W）+ 0.0147（18W）+ 0.1185（SPW）- 0.0354（FAW）。相应的指数选择差分别为0.818、0.203和0.209。父系指数选择差约占总选择差的79%。
