Breed, heterosis, and recombination effects for lactation curves in Brazilian cattle

ABSTRACT The objective of this study was to estimate the breed, heterosis, and recombination effects on different components of the lactation curve of Girolando cattle. The dataset used consisted of 12,121 purebred cows of Holstein (H) and Gyr (G) breeds, and six H×G crossbred cows (Girolando). The model used presents random effects of herd and cow, regression coefficient associated with linear effect of proportion of H breed, regression coefficient associated with the linear effect of heterosis between H and G breeds, regression coefficient associated with the linear effect of recombination between H and G breeds, and random effect of residual. Dijkstra's (DJ), Nelder's (ND), Wilmink's (WL), and Wood's (WD) models were tested to fit production records of these different genetic groups. These models were then tested according to evaluation criteria of quality of fit (AIC, BIC, and RMSE), and the two best models (WD and WL) were chosen for estimation of 305-day milk yield (MY305), peak yield, time to peak, and persistency of milk yield. The breed effect was significant for all traits and components of the lactation curve. The heterosis effect was significant for all traits, and was more significant for MY305 (945.62±79.17 kg). Peak yield was the component of lactation curve that presented the most significant heterosis effect, partially explaining the heterosis effect (12 to 21%) found for MY305. The recombination effect was positive only for lactation period and time to peak of lactation in Girolando cows.

摘要 本研究旨在评估品种效应、杂种优势效应及重组效应对吉洛兰多（Girolando）奶牛泌乳曲线各组分的影响。所用数据集包含12121头纯种荷斯坦（Holstein，H）与吉尔（Gyr，G）奶牛，以及6头H×G杂交奶牛（吉洛兰多）。本研究采用的模型包含畜群与奶牛的随机效应，与荷斯坦品种比例线性效应相关的回归系数、荷斯坦与吉尔品种间杂种优势线性效应对应的回归系数、二者间重组效应线性效应对应的回归系数，以及残差随机效应。本研究选取Dijkstra（DJ）模型、Nelder（ND）模型、Wilmink（WL）模型与Wood（WD）模型，对不同遗传群体的产奶记录进行拟合；随后基于拟合优度评价指标（AIC、BIC及均方根误差RMSE）对各模型进行检验，最终筛选出表现最优的两个模型（WD与WL），用于估计305天产奶量（MY305）、峰值产奶量、泌乳峰值时间以及产奶持续性。结果显示，品种效应对所有泌乳曲线性状及组分均具有显著影响；杂种优势效应对所有性状均显著，且在305天产奶量上的效应最为显著（945.62±79.17 kg）。峰值产奶量是泌乳曲线各组分中杂种优势效应最显著的指标，可部分解释305天产奶量所观测到的12%~21%杂种优势效应。重组效应仅在吉洛兰多奶牛的泌乳时长及泌乳峰值时间上呈现正向作用。