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.

The improvement of the reproductive traits of animals is of great interest for livestock production. Due to its positive impact on the sheep industry’s profitability, prolificacy is one of the most economically significant biological traits, showing variation between and within breeds of domestic sheep (Ovis aries). Different mutations in BMPR-1B, BMP15 and GDF9 genes coding for the transforming growth factor-β (TGFβ) superfamily have been shown to influence the ovulation rate and litter size. Numerous single-nucleotide polymorphisms (SNPs) in the bone morphogenetic protein 15 (BMP15) gene have been linked to ewe fecundity. Using targeted PCR amplification and Sanger sequencing, we were able to identify heterozygous SNPs in exon 2 of BMP15 in three sheep breeds reared in Romania: Tsigai, Cluj Merino and Tsurcana. The sequence analysis revealed three previously documented mutations, namely the missense mutation c.755T>C (L252P), which is predicted to change the tertiary structure of the BMP15 protein, and two silent mutations, c.747T>C (P249P) and c.1047G>A (V349V). In addition, we also identified one novel silent mutation, c.825G>A (S275S). Based on our findings and publicly available data, we indicate four putative mutational hotspots within exon 2 of BMP15 that could be considered for improving the indigenous sheep breeds through targeted gene editing and SNP genotyping strategies.