Effect of BMPRIB gene on litter size of sheep in China: A meta-analysis.

Genes or genetic markers related to litter size have been studied for many years in gene selection or marker-assisted selection experiments. The bone morphogenetic protein receptor IB (BMPRIB) gene is one of the candidate genes for increasing litter size of sheep. Results of studies with different sheep breeds in China have been inconsistent with some confirming significant associations between the BMPRIB gene polymorphism and litter size and with other results being inconsistent with there not being an association. In the present study, a meta-analysis was conducted evaluating 21 studies in which 5089 samples were utilized to analyze the genetic effects of BMPRIB genes on litter size in different sheep breeds in China. Results for weighted mean differences (WMD) among BMPRIB genotypes indicated there was an association between the BPRIB gene polymorphism and litter size. Effects of the BMPRIB gene on litter size are remarkably consistent in many sheep populations of China, with each gene copy being associated with an increase in litter size of 0.4 to 0.5 lambs. There are, however, some populations in which there is no effect of a second copy of the B allele. An example is the Zeller black sheep. Furthermore, in the Tan sheep and its crosses, there was no effect of the BMPRIB gene on litter size. In conclusion, with this study, there is a summarizing of magnitude of BMPRIB gene effects on litter size for sheep breeds in China, and these results provide reference information for consideration in indigenous sheep breeding programs.