Appropriate mathematical models to describe the lactation curves of milk production traits of Iranian Holstein dairy cattle

ABSTRACT. The objective of this study was to compare the goodness of fit of lactation curve models; Wood, Wilmink, Linear Splines (SPL), Cubic Splines (SPC), Quadratic Splines (SPQ), Cobby and Le Du, Ali Schaeffer and Legendre Polynomial (LEG), in random regression model (RRM) for milk production traits of Iranian Holstein dairy cattle. For this purpose the records obtained from Test-day (TD) regarding milk (928513), fat (788577) and protein (653317) yields related to their first parity were used. These data collected from the years of 2003 to 2011 by the Karaj breeding center of Iran. The genetic parameters were estimated using REML method using WOMBAT software. Based on obtained results, RRM with SPL6 (6,6), SPC6 (6,6) and LEG (3,5) for milk yield, SPL6 (6,6), SPQ6 (6,6), LEG (3,5) for fat yield and SPL5 (5,5), SPQ4 (4,4) and LEG (3,4) for protein yield, were selected as better model to describe the lactation curves. The estimated heritabilities by best models were lower in the beginning lactation than other during lactation. The genetic trend of milk yields was showed an increasing during the 10 past years, which indicated Iranian Holstein dairy cattle population genetically was improved for milk yields.

摘要：本研究旨在针对伊朗荷斯坦奶牛的产奶性状，比较随机回归模型（random regression model, RRM）中各泌乳曲线模型的拟合优度，所涉模型包括Wood、Wilmink、线性样条（Linear Splines, SPL）、三次样条（Cubic Splines, SPC）、二次样条（Quadratic Splines, SPQ）、Cobby与Le Du模型、Ali Schaeffer模型以及勒让德多项式（Legendre Polynomial, LEG）。本研究所用数据来自伊朗卡拉育种中心2003至2011年的采集记录，涵盖第一胎次奶牛的乳产量（928513条）、乳脂产量（788577条）及乳蛋白产量（653317条）的测定日（Test-day, TD）记录。本研究采用WOMBAT软件，通过限制性最大似然法（REML）估算遗传参数。基于研究结果，针对乳产量，拟合效果最优的随机回归模型为SPL6(6,6)、SPC6(6,6)及LEG(3,5)；针对乳脂产量，最优模型为SPL6(6,6)、SPQ6(6,6)及LEG(3,5)；针对乳蛋白产量，最优模型为SPL5(5,5)、SPQ4(4,4)及LEG(3,4)，上述模型均可较好地描述泌乳曲线。通过最优模型估算的遗传力在泌乳初期低于泌乳期其他阶段。近10年来乳产量的遗传趋势呈上升态势，表明伊朗荷斯坦奶牛种群的乳产量遗传性状已得到改良。