Buckley F, Dillon P, Rath M, Veerkamp R F
Department of Animal Science, Faculty of Agriculture, University College Dublin, Belfield, Ireland.
J Dairy Sci. 2000 Aug;83(8):1878-86. doi: 10.3168/jds.S0022-0302(00)75060-0.
The objectives of this study were to estimate the effects of genetic merit for milk yield on energy balance, DM intake (DMI), and fertility for cows managed on three different grass-based feeding systems and to estimate possible interactions between genetic merit and feeding system. Individual animal intake estimates were obtained at pasture on 11 occasions across three grazing seasons. The data set contained 96 first lactation, 96 second lactation, and 72 third lactation cows in 1995, 1996, and 1997, respectively. Half of these cows were of high genetic merit, and half were of medium genetic merit for milk solids production. Genetic effects for the traits of interest were estimated as the contrast between the two genetic groups and by the genetic regression of phenotypic performance on the estimated breeding value for fat and protein yield, based on pedigree index. Significant effects of feeding system were observed on yields, DMI, and energy balance, with no effect on live weight, condition score, or reproductive performance. The interaction between genetic merit and feeding system was not significantly different from zero for any of the traits. Yields, grass DMI, and total DMI were all higher for cows of high genetic merit than for those of medium genetic merit and were positively correlated (P < 0.001) with pedigree index. Furthermore, condition score, conception to first and second services, and pregnancy rate were significantly negatively correlated with pedigree index. While at pasture, energy balance was positively (P < 0.01) correlated with pedigree index, although the contrast between high genetic merit and medium genetic merit was not significantly different from zero. This positive energy balance was unexpected and was probably due to the lactation stage that intake was measured. Condition score changes and energy balance measures on a small subgroup of the animals, while indoors offered a diet of silage and concentrates (n = 33), demonstrated that high genetic merit had a more negative energy balance than did medium genetic merit. The results clearly illustrate the production potential of high genetic merit cows on grass-based systems. The reduced reproductive performance questions the suitability of high yield for seasonal calving systems.
本研究的目的是评估产奶量的遗传优势对采用三种不同的基于牧草的饲养系统管理的奶牛能量平衡、干物质摄入量（DMI）和繁殖力的影响，并评估遗传优势与饲养系统之间可能存在的相互作用。在三个放牧季节的11个不同时间点，在牧场获取了个体动物的摄入量估计值。该数据集分别包含1995年、1996年和1997年的96头头胎泌乳奶牛、96头二胎泌乳奶牛和72头三胎泌乳奶牛。这些奶牛中有一半具有较高的遗传优势，另一半在乳固体产量方面具有中等遗传优势。基于系谱指数，通过两个遗传组之间的对比以及表型性能对脂肪和蛋白质产量估计育种值的遗传回归，估计了目标性状的遗传效应。观察到饲养系统对产量、DMI和能量平衡有显著影响，对体重、体况评分或繁殖性能没有影响。对于任何性状而言，遗传优势与饲养系统之间的相互作用与零无显著差异。遗传优势高的奶牛的产量、牧草DMI和总DMI均高于遗传优势中等的奶牛，并且与系谱指数呈正相关（P < 0.001）。此外，体况评分、首次和第二次输精受胎率以及妊娠率与系谱指数呈显著负相关。在牧场时，能量平衡与系谱指数呈正相关（P < 0.01），尽管遗传优势高的奶牛与遗传优势中等的奶牛之间的对比与零无显著差异。这种正能量平衡出乎意料，可能是由于测量摄入量时的泌乳阶段。对一小部分在室内饲喂青贮饲料和精饲料的动物（n = 33）进行的体况评分变化和能量平衡测量表明，遗传优势高的奶牛的能量平衡比遗传优势中等的奶牛更负。结果清楚地说明了遗传优势高的奶牛在基于牧草的系统中的生产潜力。繁殖性能的降低对高产是否适合季节性产犊系统提出了质疑。
