Pereira R J, Verneque R S, Lopes P S, Santana M L, Lagrotta M R, Torres R A, Vercesi Filho A E, Machado M A
Departamento de Zootecnia, Faculdade de Ciências Agrárias e Veterinárias, Universidade Estadual Paulista "Júlio de Mesquita Filho", Jaboticabal, SP, Brasil.
Genet Mol Res. 2012 Jun 15;11(2):1599-609. doi: 10.4238/2012.June.15.9.
With the objective of evaluating measures of milk yield persistency, 27,000 test-day milk yield records from 3362 first lactations of Brazilian Gyr cows that calved between 1990 and 2007 were analyzed with a random regression model. Random, additive genetic and permanent environmental effects were modeled using Legendre polynomials of order 4 and 5, respectively. Residual variance was modeled using five classes. The average lactation curve was modeled using a fourth-order Legendre polynomial. Heritability estimates for measures of persistency ranged from 0.10 to 0.25. Genetic correlations between measures of persistency and 305-day milk yield (Y305) ranged from -0.52 to 0.03. At high selection intensities for persistency measures and Y305, few animals were selected in common. As the selection intensity for the two traits decreased, a higher percentage of animals were selected in common. The average predicted breeding values for Y305 according to year of birth of the cows had a substantial annual genetic gain. In contrast, no improvement in the average persistency breeding value was observed. We conclude that selection for total milk yield during lactation does not identify bulls or cows that are genetically superior in terms of milk yield persistency. A measure of persistency represented by the sum of deviations of estimated breeding value for days 31 to 280 in relation to estimated breeding value for day 30 should be preferred in genetic evaluations of this trait in the Gyr breed, since this measure showed a medium heritability and a genetic correlation with 305-day milk yield close to zero. In addition, this measure is more adequate at the time of peak lactation, which occurs between days 25 and 30 after calving in this breed.
为了评估产奶持续性指标，利用随机回归模型对1990年至2007年间产犊的3362头巴西吉尔牛首次泌乳期的27000条测定日产奶量记录进行了分析。分别使用4阶和5阶勒让德多项式对随机、加性遗传和永久环境效应进行建模。残差方差使用五类进行建模。平均泌乳曲线使用四阶勒让德多项式进行建模。持续性指标的遗传力估计值在0.10至0.25之间。持续性指标与305天产奶量（Y305）之间的遗传相关性在-0.52至0.03之间。在对持续性指标和Y305进行高强度选择时，共同被选中的动物很少。随着对这两个性状选择强度的降低，共同被选中的动物比例更高。根据奶牛出生年份，Y305的平均预测育种值有显著的年度遗传进展。相比之下，未观察到平均持续性育种值有改善。我们得出结论，在泌乳期对总产奶量进行选择并不能识别出在产奶持续性方面具有遗传优势的公牛或母牛。在吉尔牛品种对该性状的遗传评估中，应优先选择用第31天至280天估计育种值相对于第30天估计育种值的偏差之和表示的持续性指标，因为该指标显示出中等遗传力，且与305天产奶量的遗传相关性接近零。此外，该指标在泌乳高峰期（该品种产犊后第25天至30天之间）更为适用。
