Abstract: [Objective] To explore the estimation of genetic parameters of reproductive traits and environmental influencing factors in Booroola Merino sheep, to analyze the genetic patterns of reproductive traits in polytocous sheep, and to provide a basis for the selection and breeding of polytocous lines of Booroola Merino sheep. [Methods] Booroola Merino sheep from a commercial company were used as the research subject, and their reproductive traits were subjected to genetic parameter estimation and model selection. A total of 2,048 phenotypic data of reproductive traits were collected, covering average birth weight per litter （ABW）, total birth weight per litter （TBW）, gestation days （GD）, number of lambs born per litter （NLF）, and number of lambs born alive per litter （NSLF）. The GLM procedure of SAS 9.2 software was used to analyze the fixed effects of lambing year, lambing season, ewe age, lambing type, and farm/flock. Based on the ASReml-R package of R software, four different single-trait animal models were fitted [Model 1: y=Xb+Z₁a+e; Model 2: y=Xb+Z₁a+Z₂m+e; Model 3: y=Xb+Z₁a+Z₂m+Z₃c+e （δa,m=0）; Model 4: y=Xb+Z₁a+Z₂m+Z₃c+e（δa,m≠0）], the genetic parameters of reproductive traits were estimated, and the optimal model for genetic evaluation was screened by Akaike information criterion （AIC）, Bayesian information criterion （BIC）, and likelihood ratio test. [Results] Ewe age, lambing year, lambing season, farm/flock, and lambing type significantly influenced ABW, TBW, GD, NLF, and NSLF to varying degrees. Direct heritability estimates for these traits ranged from 0.010 to 0.174. Model 4 was identified as the optimal model for evaluating ABW, GD, and NLF, while Model 3 was the optimal model for evaluating TBW and NSLF. [Conclusion] Reproductive traits of Booroola Merino sheep are significantly influenced by environmental factors, with permanent environmental effects playing a non-negligible role in sheep reproduction studies. These findings provide important support for the selection and breeding of low-heritability reproductive traits in Multi-fetal Fine-wool sheep, facilitating the development of more scientific breeding strategies to enhance sheep reproductive performance in practical farming.

Key words: Booroola Merino sheep, animal model, reproductive traits, genetic parameters