Heringstad B, Klemetsdal G, Steine T
Department of Animal and Aquacultural Sciences, Norwegian University of Life Sciences, P.O. Box 5003, N-1432 As, Norway.
J Dairy Sci. 2007 May;90(5):2419-26. doi: 10.3168/jds.2006-805.
Genetic trends for clinical mastitis (CM), ketosis (KET), retained placenta (RP), and 305-d protein yield (PY305) were calculated for 2 Norwegian dairy cattle selection experiments. The first experiment, accomplished from 1978 to 1989, included groups selected for high (HMP) and low milk production (LMP). The second experiment started in 1989 and included selection for high protein yield (HPY) and low mastitis frequency (LCM). In both experiments proven sires from the active breeding program of Norwegian Red were used as sires. To take into account that selection of sires was external to the experiment, all available data from the Norwegian Red population, including disease records for 2.7 million first-lactation cows, were analyzed with a multivariate animal model. Estimated breeding values for cows in the experiments were extracted from this analysis to calculate genetic trends in the selection groups. Genetic trends for PY305 were, as expected, positive for the HMP and HPY groups, and negative for LMP and LCM. The HMP group showed increasing genetic trends for all 3 diseases, arguably a correlated response after selection for increased milk production, whereas the LCM group showed decreasing genetic trends for CM, KET, and RP. The genetic trends for KET and RP in the LCM group are most likely correlated responses after selection against CM. After 5 cow-generations the genetic difference between HPY and LCM was 10 percentage units CM, 1.5 percentage units KET, and 0.5 percentage units RP.
对挪威的2个奶牛选育试验计算了临床型乳房炎（CM）、酮病（KET）、胎衣不下（RP）以及305天产奶期蛋白质产量（PY305）的遗传趋势。第一个试验于1978年至1989年进行，包括针对高牛奶产量（HMP）和低牛奶产量（LMP）进行选择的组。第二个试验始于1989年，包括针对高蛋白产量（HPY）和低乳房炎发病率（LCM）进行选择。在这两个试验中，均使用挪威红牛现行育种计划中的经鉴定的公牛作为父本。为了考虑到公牛的选择在试验之外，利用多变量动物模型对挪威红牛群体的所有可用数据进行了分析，这些数据包括270万头头胎奶牛的疾病记录。从该分析中提取试验中奶牛的估计育种值，以计算选择组中的遗传趋势。正如预期的那样，PY305的遗传趋势在HMP组和HPY组中为正，而在LMP组和LCM组中为负。HMP组的所有3种疾病的遗传趋势均呈上升趋势，可以说是在选择提高牛奶产量后出现的相关反应，而LCM组的CM、KET和RP的遗传趋势呈下降趋势。LCM组中KET和RP的遗传趋势很可能是在针对CM进行选择后的相关反应。经过5个母牛世代后，HPY组和LCM组之间的遗传差异为CM 10个百分点、KET 1.5个百分点和RP 0.5个百分点。
