Estimation of genetic parameters and genetic trends for growth traits in Lori Bakhtiari sheep using structural equation models

In order to estimate genetic parameters and genetic trends of growth traits in Lori Bakhtiari sheep using structural equation models and standard multivariate models, pedigree and phenotypic data which were collected from 1994 to 2011 in Lori Bakhtiari sheep breeding station were used. The studied growth traits included birth weight (BW), average daily gain from birth to weaning (ADG1), weaning weight (WW), average daily gain from weaning to six-month weight (ADG2) and six-month weight (6MW). Three different models including standard multivariate model (SMM), multivariate temporal recursive model (TRM) and multivariate fully recursive model (FRM) were considered. Based on DIC values, TRM had the highest plausibility. Under TRM, structural coefficients between BW-ADG1, ADG1-WW, WW-ADG2 and ADG2-6MW were estimated to be 9.343, 0.03, 10.632 and 0.14, respectively. Direct heritability estimates for mentioned traits were 0.32-0.29, 0.2-0.22, 0.17-0.18, 0.11-0.11 and 0.16-0.16, respectively. The estimated values for genetic trends under SMM and TRM were 6-23, 0.7-3, 69-129, 0.4-1.2 and 110-187 grams per year for BW, ADG1, WW, ADG2 and 6MW, respectively. The results of genetic analyses of growth traits indicated the necessity of considering causal relationships between the studied traits for developing efficient breeding program in Lori Bakhtiari sheep