Animal Science Department, McGill University, Ste-Anne-de-Bellevue, Montreal, QC, Canada, H9X 3V9; Council for Scientific and Industrial Research - Animal Research Institute, Accra, Ghana, 00233.
Dairy consultant, Montreal, QC, Canada.
J Dairy Sci. 2021 Feb;104(2):1951-1966. doi: 10.3168/jds.2019-17938. Epub 2020 Dec 11.
Estimated breeding values of a selection index, production, durability, health, and fertility traits from Canadian Ayrshire, Jersey, and Brown Swiss bulls and cows were used to study genetic selection differentials (GSD). The bulls and cows were born from 1950 and 1960, respectively. The GSD for the 3 Canadian dairy populations were studied along the 4-path selection model: sire-to-bull (SB), dam-to-bull (DB), sire-to-cow (SC), and dam-to-cow (DC) pathways. We also determined the variations in realized GSD due to herd and herd × year of conception in addition to the effects of some environmental factors on realized GSD of the SC and DC paths. The mean realized GSD of the DB were higher than those of other paths and were increasing for lifetime performance index, 305-d milk yield, 305-d fat yield, and 305-d protein yield in all 3 dairy cattle populations. We observed no clear trends in realized GSD for type traits in all 3 dairy cattle breeds except for the apparent increasing trends in realized GSD of mammary system, dairy strength, and feet and legs in the DB and SC paths of the Ayrshire breed. No clear patterns were observed in the realized GSD of daughter fertility in the SB, DB, and SC paths of all dairy cattle breeds. Realized GSD for somatic cell score showed increasing and favorable trends in the 3 most influential selection paths (SB, DB, and SC). Year of conception influenced realized GSD of artificial insemination bulls in Ayrshire, Jersey, and Brown Swiss dairy populations. Selection emphases for the SC path generally increased with time. There was considerable variation among herds in selection pressures applied in the SC and DC pathways but no clear association with housing system or region. This study demonstrates that variations exist among herds of minor dairy cattle breeds in their selection for economically important traits. These variations offer opportunities for further improvements in these populations.
利用加拿大亚士厘牛、娟姗牛和瑞士褐牛公牛和母牛的选种指数、生产、持久力、健康和繁殖性状的估计育种值来研究遗传选择差异（GSD）。这些公牛和母牛分别于 1950 年和 1960 年出生。研究了加拿大 3 个奶牛群体的 GSD 沿着 4 条途径选择模型：父本公牛（SB）、母本公牛（DB）、父本母牛（SC）和母本母牛（DC）途径。我们还确定了由于牛群和牛群受孕年份的变化以及一些环境因素对 SC 和 DC 途径的实际 GSD 的影响而导致的实际 GSD 的变化。DB 的平均实际 GSD 高于其他途径，并且在所有 3 个奶牛群体中，终生性能指数、305 天产奶量、305 天脂肪产量和 305 天蛋白质产量都在增加。除了在亚士厘牛 DB 和 SC 途径中发现乳腺系统、奶牛强度和蹄腿的实际 GSD 呈明显增加趋势外，我们没有观察到所有 3 个奶牛品种的体型性状的实际 GSD 有明显的趋势。在所有奶牛品种的 SB、DB 和 SC 途径中，女儿生育力的实际 GSD 没有明显的模式。体细胞评分的实际 GSD 在 3 个最具影响力的选择途径（SB、DB 和 SC）中呈增加和有利的趋势。牛群受孕年份影响了亚士厘牛、娟姗牛和瑞士褐牛奶牛群体的人工授精公牛的实际 GSD。在 SC 途径中，选择重点一般随时间而增加。在 SC 和 DC 途径中，牛群之间的选择压力存在相当大的差异，但与住房制度或地区没有明显的关系。本研究表明，在经济重要性状的选择方面，小奶牛品种的牛群之间存在差异。这些差异为这些群体的进一步改进提供了机会。
