The relationships between PRL/Rsa I polymorphism in prolactin gene and milk production in cattle: A Meta-analysis
Numerous studies have examined the association between prolactin gene polymorphisms with different traits of milk production in cow, often with conflicting results. This study was performed to investigate the association between PRL/Rsa I polymorphism and milk production by meta-analysis of various published research results. In this meta-analysis the Metafor package of R software was used to analyze the data. Based on these results, the overall effect of this gene on milk production is 0.533 with a 95% confidence interval between 0.179 to 0.887 and animals with AA genotype have higher production than animals with BB genotype (P <0.01). Subgroup analysis revealed that this difference in the function of genotypes is related to non-Holstein cows, so that cows with AA genotypes are better than BB genotype (0.66, CI 0.113 1.119, I2=80.04%), while this difference is not significant for Holstein cows (0.37, CI -0.035 0.779, I2=41.08%). It was also found that in additive, dominance, codominance, and recessive models when Holstein cows were studied, the difference in animal performance with different PRL/Rsa I genotypes was not significant. Based on these results, no association was found between PRL/Rsa I polymorphism with fat percentage and milk protein percentage in the studied populations. It is suggested that instead of focusing on variants on this gene as direct markers for the selection of dairy cows, the effect of this gene in combination with other genes in the framework of genomic selection should be considered.