Litter size is one of the most important traits in goat production and breeding. The most common and presumed single nucleotide polymorphism (SNP) detected in the Growth Differentiation Factor 9 gene is c.1189G > A (rs637044681, Ensembl) which results in an altered sequence of the encoded protein. In some studies, there was no effect of this SNP on litter size, while in other studies there was an effect. In the present study there was a meta-analysis conducted by pooling results from 11 eligible published studies to investigate effects of c.1189G > A polymorphism on litter size using four different genetic models including dominant (AA + AG compared with GG), recessive (AA compared with AG + GG), additive (AA compared with GG) and co-dominant (AA + GG compared with AG). Data were analyzed using fixed and random-effect models based on the I-squared value. Results indicate the c.1189G > A polymorphism is positively associated with litter size with use of the dominant model (SMD = 0.093, 95% CI = 0.028 to 0.158, PValue = 0.005). There, however, was no effect of the c.1189G > A polymorphism using the recessive (SMD = 0.065, 95% CI = -0.164 to 0.295, P-Value = 0.577), additive (SMD = 0.172, 95% CI = -0.169 to 0.513, P-Value = 0.324) and co-dominant (SMD = -0.083, 95% CI = -0.200 to 0.034, P-Value = 0.164) genetic models. Results from use of the sensitivity analysis indicate the GG genotype affect litter size with use of the additive model (P < 0.01). The results from this meta-analysis indicate the GG genotype is associated with litter size in goats.
