Hossein-Zadeh Navid Ghavi
Department of Animal Science,Faculty of Agricultural Sciences,University of Guilan,Rasht,41635-1314,Iran.
J Dairy Res. 2016 Aug;83(3):334-40. doi: 10.1017/S0022029916000340.
The aim of this study was to compare seven non-linear mathematical models (Brody, Wood, Dhanoa, Sikka, Nelder, Rook and Dijkstra) to examine their efficiency in describing the lactation curves for milk fat to protein ratio (FPR) in Iranian buffaloes. Data were 43 818 test-day records for FPR from the first three lactations of Iranian buffaloes which were collected on 523 dairy herds in the period from 1996 to 2012 by the Animal Breeding Center of Iran. Each model was fitted to monthly FPR records of buffaloes using the non-linear mixed model procedure (PROC NLMIXED) in SAS and the parameters were estimated. The models were tested for goodness of fit using Akaike's information criterion (AIC), Bayesian information criterion (BIC) and log maximum likelihood (-2 Log L). The Nelder and Sikka mixed models provided the best fit of lactation curve for FPR in the first and second lactations of Iranian buffaloes, respectively. However, Wood, Dhanoa and Sikka mixed models provided the best fit of lactation curve for FPR in the third parity buffaloes. Evaluation of first, second and third lactation features showed that all models, except for Dijkstra model in the third lactation, under-predicted test time at which daily FPR was minimum. On the other hand, minimum FPR was over-predicted by all equations. Evaluation of the different models used in this study indicated that non-linear mixed models were sufficient for fitting test-day FPR records of Iranian buffaloes.
本研究的目的是比较七种非线性数学模型（布罗迪模型、伍德模型、达诺阿模型、西卡模型、内尔德模型、鲁克模型和迪杰斯特拉模型），以检验它们在描述伊朗水牛乳脂肪与蛋白质比率（FPR）泌乳曲线方面的效率。数据来自伊朗水牛前三个泌乳期的43818条FPR测定日记录，这些记录由伊朗动物育种中心于1996年至2012年期间在523个奶牛场收集。使用SAS中的非线性混合模型程序（PROC NLMIXED）将每个模型拟合到水牛的月度FPR记录，并估计参数。使用赤池信息准则（AIC）、贝叶斯信息准则（BIC）和对数最大似然值（-2 Log L）对模型的拟合优度进行检验。内尔德混合模型和西卡混合模型分别对伊朗水牛第一个和第二个泌乳期的FPR泌乳曲线拟合效果最佳。然而，伍德混合模型、达诺阿混合模型和西卡混合模型对第三个泌乳期水牛的FPR泌乳曲线拟合效果最佳。对第一个、第二个和第三个泌乳期特征的评估表明，除第三个泌乳期的迪杰斯特拉模型外，所有模型都低估了每日FPR最低时的测定时间。另一方面，所有方程都高估了最低FPR。对本研究中使用的不同模型的评估表明，非线性混合模型足以拟合伊朗水牛的测定日FPR记录。
