Spurlock D M, Stock M L, Coetzee J F
Department of Animal Science, and College of Veterinary Medicine, Iowa State University, Ames 50011.
Department of Veterinary Diagnostic and Production Animal Medicine, College of Veterinary Medicine, Iowa State University, Ames 50011.
J Dairy Sci. 2014;97(8):5265-74. doi: 10.3168/jds.2013-7746. Epub 2014 Jun 7.
Dehorning in cattle has been associated with behavioral, physiological, and neuroendocrine responses indicative of pain. Unaddressed, the pain associated with a routine production procedure could contribute to a negative public perception of livestock production practices. Alternative considerations of dehorning include the selection of polled cattle within herds, thereby avoiding pain and production loss. As polledness results from an autosomal dominant pattern of inheritance, genetic selection for polled cattle could reduce the prevalence of the horned trait. Herein we discuss 3 strategies to incorporate polled genetics into a cow herd and the estimated impact on the overall genetic merit of the herd. Furthermore, the availability and genetic merit of polled artificial insemination bulls in the United States is summarized. Both Holstein and Jersey dairy bulls registered with the National Association of Animal Breeders from December 2010 through April 2013 were queried. Polled bulls were identified as either being homozygous (PP) or heterozygous (Pp) and the average net merit (NM) predicted transmitting ability (PTA) of each sire group was calculated. The percentage of polled calves born each year over a 10-yr period was calculated for the following 3 scenarios: (A) various percentages of horned cows were randomly mated to Pp bulls, (B) various percentages of horned cows were preferentially mated to Pp bulls, and (C) horned cows were selectively mated to PP bulls, heterozygous cows to Pp bulls, and homozygous polled cows to horned bulls. Additionally, the change in NM PTA of the cow herd was calculated over the same period. The highest percentage of polled animals (87%) was achieved in scenario C. An evaluation of the herd NM PTA highlights the trade-offs associated with increasing polled genetics. Given the current genetic merit of horned and polled bulls, increasing the percentage of polled calves will decrease the NM PTA in Holstein, but may have minimal impact in Jersey herds. Decisions regarding selective breeding to increase polled genetics will need to be evaluated in the context of production objectives, cost of dehorning, and impact on overall genetic merit.
给牛去角与表明疼痛的行为、生理和神经内分泌反应有关。若不加以处理，与常规生产程序相关的疼痛可能会导致公众对畜牧生产方式产生负面看法。去角的替代方案包括在牛群中选择无角牛，从而避免疼痛和生产损失。由于无角性状是由常染色体显性遗传模式决定的，对无角牛进行基因选择可以降低有角性状的发生率。在此，我们讨论将无角基因纳入奶牛群的三种策略以及对牛群整体遗传价值的估计影响。此外，还总结了美国无角人工授精公牛的可用性和遗传价值。查询了2010年12月至2013年4月在全国动物育种者协会注册的荷斯坦和泽西奶牛公牛。将无角公牛鉴定为纯合子（PP）或杂合子（Pp），并计算每个父本群体的平均净遗传价值（NM）预测传递能力（PTA）。计算了以下三种情况下10年期间每年出生的无角犊牛的百分比：（A）不同比例的有角母牛随机与Pp公牛交配，（B）不同比例的有角母牛优先与Pp公牛交配，（C）有角母牛与PP公牛选择性交配，杂合母牛与Pp公牛交配，纯合无角母牛与有角公牛交配。此外，还计算了同一时期牛群NM PTA的变化。在情况C中实现了最高比例的无角动物（87%）。对牛群NM PTA的评估突出了增加无角基因相关的权衡。鉴于目前有角和无角公牛的遗传价值，增加无角犊牛的比例将降低荷斯坦牛群的NM PTA，但对泽西牛群的影响可能最小。关于通过选择性育种增加无角基因的决策需要在生产目标、去角成本以及对整体遗传价值的影响的背景下进行评估。
