Coffey M P, Hickey J, Brotherstone S
Sustainable Livestock Systems, Scottish Agricultural College, Edinburgh EH9 3JG, UK.
J Dairy Sci. 2006 Jan;89(1):322-9. doi: 10.3168/jds.S0022-0302(06)72097-5.
In general, genetic selection is applied after first calving to traits that manifest themselves during the animal's productive life, mostly during the early part of productive life. This selection policy has had undesirable correlated responses in other economically important traits, such as health and fertility, and may also have had an effect on the growth of animals both during productive life and before first calving. In this study, we analyzed the growth trajectory of dairy heifers that had been selected for maximum production of combined fat and protein (measured in kg; select line) or for average production (control line) in the United Kingdom. Before first calving, these divergent lines were managed as a single group. Select line heifers grew faster than did control line heifers. They were also heavier at first calving, but by the end of 3 lactations, the lines were not significantly different in live weight. Selection primarily for yield and for other traits has led to heifers that grow faster and reach higher growth rates earlier in life. A genetic analysis of birth, weaning, and calving weights yielded heritability estimates of 0.53 (birth weight), 0.45 (weaning weight), and 0.75 (calving weight). Confidence intervals for the genetic correlations between the traits indicated that these BW traits are not under the same genetic control.
一般来说，基因选择是在首次产犊后应用于那些在动物生产期，主要是生产期早期表现出来的性状。这种选择策略在其他经济上重要的性状，如健康和繁殖力方面产生了不良的相关反应，并且可能也对动物在生产期以及首次产犊前的生长有影响。在本研究中，我们分析了英国那些被选择用于最大化脂肪和蛋白质总产量（以千克衡量；选择系）或平均产量（对照系）的奶牛小母牛的生长轨迹。在首次产犊前，这些不同的品系作为一个单一群体进行管理。选择系的小母牛比对照系的小母牛生长得更快。它们在首次产犊时也更重，但到第3个泌乳期结束时，两个品系的活体重没有显著差异。主要针对产量和其他性状的选择导致小母牛生长更快且在生命早期达到更高的生长速率。对出生、断奶和产犊体重进行的遗传分析得出遗传力估计值分别为0.53（出生体重）、0.45（断奶体重）和0.75（产犊体重）。这些性状之间遗传相关性的置信区间表明这些体重性状并非受相同的遗传控制。
