Methods of Improving Reproductive Parameters in Sheep and The Major Genes Associated with Prolificacy: A Review

Farm profitability is heavily influenced by reproductive capacity. Fertility, prolificacy, and fecundity are all indicators of reproductive efficiency. In sheep with high economic value, prolificacy is a key reproduction parameter (Notter, 2008). Because most sheep breeds are monotocous, similar to Mouflon wild sheep (Garel et al., 2005), improving fecundity is a serious concern (Tang et al., 2019). This review aims to study genes and the genetic means of improving sheep reproduction parameters. Numerous mutations in the transforming growth factor (TGF) superfamily have been reported to influence sheep reproductive parameters. As a result, molecular genetics and marker-assisted selection (MAS) are essential in improving reproduction efficiency. If these mutations are not present in the population, introgression of the beneficial mutations to indigenous breeds is possible. Because within-breed selection has been considered relatively inefficient, due to the low heritability of the trait, crossbreeding of native breeds with prolific breeds has been the major means of genetically improving prolificacy. Studying fecundity genes is important in order to increase production efficiency and stabilizing optimal litter sizes. Different studies based on whole-genome sequencing (WGS), which are called genome-wide association studies (GWAS), and also proteomic studies, transcriptome analysis, and mitochondrial DNA analysis have revealed further genetic variation with medium or minor effects on reproduction.