This study aimed to infer the causal effects of birth weight on growth curve traits as well as, assessment of causal relationships among the growth curve traits in Lori-Bakhtiari sheep using structural equation modeling. The body weight-age records were collected from birth to 390 days of age from 1995 to 2012 in Shooli Breeding Station of Lori-Bakhtiari sheep, Shahr-e Kord, Iran. Initially, five non-linear models including Brody, Logistic, Negative exponential, Gompertz and von Bertalanffy were fitted on 22,546 body weight-age records for determining the best model describing the growth curve. Among the tested non-linear growth models, Brody model showed the best goodness of fit. Then, data on growth curve traits of 3,168 lambs from 217 rams and 1,211 ewes were considered for genetic evaluation of growth curve traits including asymptotic weight (A), integration constant related to initial animal weight (b), and maturation rate (k).The causal effect of birth weight (BW) on growth curve traits under two models including standard multivariate model (SMM) and fully recursive model (FRM) were fitted via a Bayesian approach. The posterior means of heritability for the growth curve traits were similar under both SMM and FRM, while the posterior means of genetic correlations among the traits were statistically different under both SMM and FRM. Structural coefficients related to causal effects of BW on b, k and A, were statistically significant with values −0.19, 0.01and 12.58, respectively. Therefore, considering the causal effects of BW on growth curve traits is essential for accurate genetic analysis of growth curve traits of Lori-Bakhtiari sheep.

本研究旨在推断出生体重对生长曲线性状的因果影响，并使用结构方程模型评估 Lori-Bakhtiari 绵羊生长曲线性状之间的因果关系。1995 年至 2012 年在伊朗 Shahr-e Kord 的 Lori-Bakhtiari 羊 Shooli 育种站收集了从出生到 390 日龄的体重-年龄记录。最初，包括 Brody、Logistic、负指数、Gompertz 和 von Bertalanffy 在内的五个非线性模型被拟合到 22,546 个体重-年龄记录上，以确定描述生长曲线的最佳模型。在测试的非线性增长模型中，Brody 模型表现出最佳的拟合优度。然后，来自 217 只公羊和 1 只公羊的 3,168 只羔羊的生长曲线性状数据，211 只母羊被考虑用于生长曲线性状的遗传评估，包括渐近体重 (A)、与初始动物体重相关的积分常数 (b) 和成熟率 (k)。出生体重 (BW) 对生长曲线性状的因果影响通过贝叶斯方法拟合了包括标准多元模型（SMM）和完全递归模型（FRM）在内的两个模型。SMM和FRM下生长曲线性状遗传力的后验均值相似，而SMM和FRM下各性状间遗传相关性的后验均值差异有统计学意义。与 BW 对 b、k 和 A 的因果效应相关的结构系数在统计上显着，分别为 -0.19、0.01 和 12.58。因此，