Estimation of genetic and phenotypic trends for dairy traits of Gyr and Guzerá breeds

ABSTRACT. Milk production has high economic importance in dairy cattle production systems, which justifies its inclusion in genetic breeding programs. The objective of this study was to evaluate the genetic and phenotypic trends of dairy traits in Gyr (167 lactations) and Guzerá (148 lactations) breeds in the State of Rio Grande do Norte (RN). Milk, fat and protein production obtained from monthly dairy controls were the traits evaluated. The expected differences in progeny (DEPs) for these traits were estimated using an animal model. From the means of phenotypic values and DEPs, we estimated the genetic and phenotypic trends in linear regressions as a function of the year of calving of the animal. Positive genetic and phenotypic trends were observed for Gyr (26.8 and 88.7 kg year-1) and Guzerá (8.44 and 37.68 kg year-1). Gyr breed presented positive genetic trends for fat (1.08 kg year-1) and protein (0.45 kg year-1) production and the Guzerá breed showed positive genetic trends for fat (0.36 kg year-1) and protein (0.25 kg year-1) production. The selection applied in the evaluated herds has produced satisfactory genetic and phenotypic progress for milk, fat and protein production.

摘要。乳用牛生产体系中，牛乳产量具有极高的经济价值，故将其纳入奶牛遗传育种计划具有充分依据。本研究旨在评估北里奥格兰德州（RN）内吉尔牛（Gyr，167次泌乳记录）与古泽拉牛（Guzerá，148次泌乳记录）的乳用性状遗传趋势与表型趋势。本次研究评估的性状为通过月度泌乳检测获得的产奶量、乳脂量与乳蛋白量。研究采用动物模型，估算了上述性状的预期后代差异（Expected Differences in Progeny，DEPs）。基于表型值与DEPs的均值，本研究以动物产犊年份为自变量，通过线性回归分析估算遗传趋势与表型趋势。结果显示，吉尔牛与古泽拉牛均呈现正向遗传趋势与表型趋势：吉尔牛的对应趋势分别为26.8 kg·年⁻¹与88.7 kg·年⁻¹，古泽拉牛则分别为8.44 kg·年⁻¹与37.68 kg·年⁻¹。此外，吉尔牛的乳脂产量（1.08 kg·年⁻¹）与乳蛋白产量（0.45 kg·年⁻¹）均呈现正向遗传趋势，古泽拉牛的乳脂产量（0.36 kg·年⁻¹）与乳蛋白产量（0.25 kg·年⁻¹）同样呈现正向遗传趋势。本次评估牛群所实施的选育工作，在产奶量、乳脂量与乳蛋白量性状上均取得了令人满意的遗传与表型进展。