Meta-analysis and systematic review of genetic parameter estimates and candidate genes for growth traits in sheep

ABSTRACT The objective of this study was to unravel the genetic architecture of growth traits in sheep through a meta-analysis of genetic parameters (i.e., direct, maternal, and total heritability estimates, as well as genetic correlations), a systematic review, and a functional analysis to identify candidate genes and metabolic pathways related to growth traits. A random effects model was used to obtain the pooled effect estimates for the genetic parameters, and heterogeneity was assessed using both I2 and Cochran’s Q statistics. For the systematic review, genomic regions were searched in the selected scientific papers, and genes were identified using the Biomart tool. After quality control, 118 articles comprising nine traits, 504 heritability estimates, and 74 genetic correlation estimates were used for the meta-analysis, and 14 articles remained for the systematic review of the genomic regions. The pooled direct heritability estimates across studies ranged from 0.07 (±0.04) for weaning weight to 0.29 (±0.03) for weight at nine months. The systematic review identified 461 genes in the significant genomic regions. These genes were distributed across all chromosomes, with most of them located on OAR11. Some regions on chromosomes 6, 15, and 21 exhibited pleiotropic effects across traits. Pathways were mainly associated with developmental and lipid metabolic processes. Growth traits in sheep are complex, have low to moderate heritabilities, and are influenced by several genes of small effect, some of which of pleiotropic effect.