Lopez-Villalobos N, Garrick D J, Blair H T, Holmes C W
Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Pamerston North, New Zealand.
J Dairy Sci. 2000 Jan;83(1):154-63. doi: 10.3168/jds.S0022-0302(00)74866-1.
A deterministic model was developed to evaluate the concurrent effects of selection and crossbreeding on the rate of genetic gain and productivity of New Zealand dairy cattle over 25 yr. Selection was based on an index, which included estimated breeding values for mature cow live weight and lactation yields of milk, fat, and protein. Mating strategies involving Holstein-Friesian, Jersey, and Ayrshire breeds were evaluated. Effects of heterosis and age were included to calculate live weight and yields of milk, fat, and protein per cow. Feed requirements were estimated for maintenance, lactation, and pregnancy and for replacement heifers. Stocking rate was calculated by assuming 12,000 kg of dry matter annually utilized per hectare. Upgrading to either Jersey or Holstein-Friesian increased the number of potential bull mothers and resulted in genetic gains of 0.27 genetic standard deviations/yr for both options. Rotational crossbreeding of Holstein-Friesian x Jersey decreased the number of potential bull mothers and resulted in a genetic gain of 0.24 genetic standard deviations/yr. Upgrading to Jersey resulted in the least increase in milk (5%) and the greatest increase in fat (16%) and protein (27%) per hectare with a small decrease in stocking rate (0.4%). Upgrading to Holstein-Friesian reduced the stocking rate by 11% and increased production of milk, fat, and protein per hectare by 10, 8, and 21%, respectively. Rotational crossbreeding of Holstein-Friesian x Jersey resulted in greater production per hectare than the intermediate production between upgrading to Jersey and upgrading to Holstein-Friesian. Crossbreeding can be used in combination with selection to exploit the effects of heterosis while maintaining genetic diversity to cover changes in market conditions.
开发了一个确定性模型，以评估选择和杂交育种对新西兰奶牛25年期间遗传增益率和生产力的协同影响。选择基于一个指数，该指数包括成年母牛活重以及牛奶、脂肪和蛋白质泌乳量的估计育种值。评估了涉及荷斯坦-弗里生、泽西和艾尔郡品种的交配策略。纳入杂种优势和年龄的影响，以计算每头母牛的活重以及牛奶、脂肪和蛋白质产量。估计了维持、泌乳和怀孕以及后备小母牛的饲料需求。通过假设每公顷每年利用12,000千克干物质来计算载畜率。升级为泽西或荷斯坦-弗里生都会增加潜在公牛母亲的数量，两种选择的遗传增益均为每年0.27个遗传标准差。荷斯坦-弗里生×泽西的轮回杂交减少了潜在公牛母亲的数量，遗传增益为每年0.24个遗传标准差。升级为泽西导致每公顷牛奶增加最少（5%），脂肪增加最多（16%）和蛋白质增加最多（27%），载畜率略有下降（0.4%）。升级为荷斯坦-弗里生使载畜率降低了11%，每公顷牛奶、脂肪和蛋白质产量分别增加了10%、8%和21%。荷斯坦-弗里生×泽西的轮回杂交导致每公顷产量高于升级为泽西和升级为荷斯坦-弗里生之间的中间产量。杂交育种可与选择结合使用，以利用杂种优势的影响，同时保持遗传多样性以应对市场条件的变化。
