The aim of this study was to evaluate the heterosis effects for 305-day milk yield (305MY) in different lactation orders of Girolando cows, by fitting test-day milk yield records to Wood's, Mixed Log, and Wilmink's non-linear models. A total of 400,328 test-day milk yield records of 39,077 Holstein (H), Gyr (G), and Girolando (1/2 H, 1/4 H, 3/4 H, 3/8 H, 5/8 H, and 7/8 H genetic groups) cows from 822 herds were collected in the state of Minas Gerais, Brazil, from 1998 to 2014. The pedigree file comprised 36,640 animals, including 3677 sires and 24,472 cows. Genetic parameters were obtained by single-trait analysis using the AIREMLF90 software. Heritability estimates of 305MY and of 305MY fitted to the different non-linear models were higher in the first lactation and ranged from 0.10 to 0.29. We observed a greater heterosis effect for 305MY (and 305MY fitted) verified in cows of genetic group 1/2H, which presented average production superior to the average of their parents (of pure breeds) in the first (1034.33 kg) and second (1303.94 kg) lactation, respectively. Both Wood's and Wilmink's models stood out in quality of fit, presenting the best estimates for 305MY adjusted for different lactation orders. Wood's model is the most suitable to estimate 305MY of cows with a higher proportion of H genes. However, Wilmink's model allows estimating heterosis effects for 305MY and components of the lactation curve more similar to those observed in 305MY in the different genetic groups. The results indicate that local breeders can promote an improvement in milk production through exploitation of the heterosis effect, making choices of genetic combinations (breeders) more suitable for mating to obtain greater economic and productive efficiency of their herds during lactations.

这项研究的目的是通过将测试日奶量记录拟合到Wood's，Mixed Log和Wilmink的非线性模型，评估吉罗兰多奶牛不同泌乳顺序下305天奶量（305MY）的杂种优势。共有400328个测试日的牛奶产量记录，分别为39077荷斯坦（H），吉尔（Gyr）和吉罗兰多（1/2 H，1/4 H，3/4 H，3/8 H，5/8 H，和7/8 H基因组），从1998年至2014年在巴西米纳斯吉拉斯州（Minas Gerais）收集了来自822个牛群的母牛。家谱档案包括36,640只动物，包括3677头公牛和24,472头牛。使用AIREMLF90软件通过单性状分析获得遗传参数。305MY和适用于不同非线性模型的305MY的遗传力估计值在第一次哺乳期较高，范围在0.10至0.29之间。我们观察到在基因组1 / 2H的奶牛中验证的305MY（和305MY拟合）的杂种优势更大，在第一个（1034.33千克）和第二个（1303.94）种中，平均产量要高于其纯种的父母平均水平。公斤）泌乳。Wood和Wilmink的模型在贴合质量上均脱颖而出，提出了针对不同泌乳期调整后的305MY的最佳估算值。伍德模型最适合估算H基因比例较高的母牛的305MY。但是，Wilmink模型可以估算305MY的杂种优势，而泌乳曲线的组成与不同基因组中305MY所观察到的相似。结果表明，本地育种者可以通过利用杂种优势效应来促进牛奶产量的提高，