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：牛奶产量在奶牛养殖体系中具有极高的经济价值，因此将其纳入遗传育种计划具有充分合理性。本研究旨在评估北里奥格兰德州（RN）吉尔牛（Gyr，167个泌乳期）与古泽西牛（Guzerá，148个泌乳期）的泌乳性状遗传趋势与表型趋势。本研究评估的性状为通过月度泌乳记录获取的牛奶产量、乳脂产量与乳蛋白产量。采用动物模型估算上述性状的后代期望差异（DEPs）。基于表型值均值与后代期望差异，以动物产犊年份为自变量，通过线性回归估算遗传趋势与表型趋势。结果显示，吉尔牛的遗传与表型趋势分别为26.8千克/年与88.7千克/年，古泽西牛则分别为8.44千克/年与37.68千克/年。吉尔牛的乳脂产量（1.08千克/年）与乳蛋白产量（0.45千克/年）均呈现正向遗传趋势，古泽西牛的乳脂产量（0.36千克/年）与乳蛋白产量（0.25千克/年）亦呈现正向遗传趋势。本研究所涉及牛群所实施的选择育种，已在牛奶、乳脂与乳蛋白产量方面取得了令人满意的遗传与表型进展。