Nonlinear mixed effects models for comparing growth curves for Guzerá cattle

ABSTRACT The objective of the present work was to evaluate the accuracy of the fitted Gompertz and von Bertalanffy models for male and female Guzerá cattle, respectively. Four production regions in Northeast Brazil were included in the models as a fixed effect, and the animals were included as a random effect. In addition, the coefficients of the growth models in the production regions were compared. The accuracy of the fit equations was assessed with the Akaike information criterion, Bayesian information criterion, mean absolute deviation, mean squared error, and coefficient of determination. Confidence intervals were used for comparing the production regions. The Guzerá males in the Gado-Algodão and Serra Geral da Bahia production regions were statistically equal in asymptotic weight, and the animals in the Itapetinga-Valadares and Mata-Agreste regions had equivalent maturity rates. The Guzerá females in the Itapetinga-Valadares and Serra Geral da Bahia regions had the same asymptotic weight. The maturity rates in Itapetinga-Valadares were equal to those estimated for Mata-Agreste and Serra Geral da Bahia. The inclusion of the fixed effect of the production region and the random effect of the animals in the models improved the fit quality and increased the possibility of generating growth curves for each region.

摘要 本研究旨在分别评估龚珀兹模型（Gompertz）与冯·贝塔朗菲模型（von Bertalanffy）对公、母古兹拉牛的拟合精度。本研究将巴西东北部4个生产区域纳入模型作为固定效应，以个体动物作为随机效应，并对各生产区域内生长模型的参数开展对比分析。拟合方程的精度通过赤池信息准则（Akaike information criterion）、贝叶斯信息准则（Bayesian information criterion）、平均绝对偏差、均方误差及决定系数进行评估，同时采用置信区间对各生产区域进行对比分析。巴伊亚州Gado-Algodão与Serra Geral da Bahia产区的古兹拉公牛渐近体重无统计学差异，Itapetinga-Valadares与Mata-Agreste产区的公牛成熟速率相当；Itapetinga-Valadares与Serra Geral da Bahia产区的古兹拉母牛渐近体重一致，该产区母牛的成熟速率与Mata-Agreste及Serra Geral da Bahia产区的估算值无显著差异。在模型中纳入生产区域固定效应与个体动物随机效应，可提升模型拟合质量，同时为各产区生成专属生长曲线拓展了可行空间。