Frahm R R, Nichols C G, Buchanan D S
J Anim Sci. 1985 Jun;60(6):1385-95. doi: 10.2527/jas1985.6061385x.
Selection was applied from 1964 to 1978 for increased weaning weight (WWL) or yearling weight (YWL) in two Hereford lines. An Angus line was maintained as an unselected control line (CL). Each line was maintained with 50 cows and four sires each year (two sires selected each year and used for 2 yr). Primary traits measured in the lines were birth weight (BW), preweaning daily gain (WDG), weaning weight (WW), weaning conformation grade (WG), weaning condition score (WC), weaning to yearling daily gain (YDG), yearling weight (YW), yearling conformation grade (YG) and yearling condition score (YC). Averaged over two methods, estimated genetic responses/generation (in standard deviation units) in WWL and YWL were: BW, .29, .26; WDG, .17, .15; WW, .22, .19; WG, .19, .26; WC, .12, .12; YDG, -.02, .04; YW, .08, .14; YG, .19, .16; YC, -.13, -.03. The realized heritability estimates were .23 and .15 for WW and YW, respectively. The realized genetic correlation between WW and YW was .69. Progeny from crosses of selected WWL and YWL sires to Angus cows had similar feedlot and carcass performance. At the end of the study, milk yield and composition were similar for mature cows in WWL and YWL.
1964年至1978年期间，对两个赫里福德品系进行了选育，以提高断奶体重（WWL）或周岁体重（YWL）。安格斯品系作为未选育的对照品系（CL）。每个品系每年保持50头母牛和4头公牛（每年选择2头公牛并使用2年）。在这些品系中测量的主要性状有出生体重（BW）、断奶前日增重（WDG）、断奶体重（WW）、断奶体型评分（WG）、断奶体况评分（WC）、断奶至周岁日增重（YDG）、周岁体重（YW）、周岁体型评分（YG）和周岁体况评分（YC）。两种方法的平均值显示，WWL和YWL中估计的每代遗传反应（以标准差单位计）为：BW，0.29，0.26；WDG，0.17，0.15；WW，0.22，0.19；WG，0.19，0.26；WC，0.12，0.12；YDG，-0.02，0.04；YW，0.08，0.14；YG，0.19，0.16；YC，-0.13，-0.03。WW和YW的实际遗传力估计值分别为0.23和0.15。WW和YW之间的实际遗传相关性为0.69。选择的WWL和YWL公牛与安格斯母牛杂交的后代在饲养场和胴体性能方面相似。在研究结束时，WWL和YWL中成熟母牛的产奶量和乳成分相似。
