Associations between STAT5A Gene Polymorphisms and Some Milk Production Traits in Dairy Cows: A Systematic Review and Meta-Analysis

The current study aimed to investigate and compare STAT5A/AvaI gene polymorphisms and their relationship with milk production traits including milk yield, fat, and protein contents by meta-analysis. A total of 11 studies from 2008 to 2023 were included in the comprehensive search. Three co-dominant models (CT vs. CC), (CT vs. TT) and (CC vs. TT) were used to analyze data. The standardized mean difference (SMD) was used to measure the size effects. 95% confidence intervals were calculated using random/fixed effect models. Heterogeneity among studies and statistical stability of overall estimates were assessed using I-2 tests by Stata 11.2 software. The association analysis found higher heterogeneity among the studies indicating higher genetic variability. In the results, a significant association was found between the additive model (CT vs. CC) and protein content (P < 0.05). No significant associations were found between STAT5A/AvaI gene polymorphisms with lactation milk yield and fat content. It was concluded that STAT5A gene polymorphisms in dairy cattle breeds could be used as good markers for protein improvement. Several studies reported by the authors contradicted this study. Therefore more investigation should be done to determine the polymorphism of the STAT5A gene and its effect on milk yield and fat content in dairy cattle.