Meta-analysis of Genetic Structure and Association of Prolactin Gene with Performance Traits in Dairy Cattle in India.

The present meta-analysis was carried to provide the more reliable estimates of gene frequency and association of Rsa 1 generated candidate genotype of prolactin gene within exon-3 with performance traits in 1198 Indian dairy cows using data from 15 published studies. Six genetic models viz., codominant (AA vs. AB, AA vs. BB and AB vs. BB), dominant (AA+AB vs. BB), completely over dominant (AA+BB vs. AB) and recessive (AA vs. AB+BB) were used to obtain standardized mean difference (SMD) between genotypes. Meta-analysis showed that the gene frequency of A allele (156 bp) was 0.60 (95% confidence interval (CI) 0.54, 0.65). In association analysis, cows with AB genotype [SMD = 0.65, 95% CI 0.00, 1.30] had significantly (P < 0.05) higher lactation milk yield (LMY) as compared to BB genotype, whereas AA and AB genotypes had similar trend. Likewise, AA + AB also had larger effect [SMD = 2.31, 95% CI 0.21, 4.10] on LMY as compared to BB. Cows with AB genotype had significantly lower age at first calving (AFC) with small effect [SMD (AA vs. AB) = 1.38, 95% CI 0.06, 2.70] and medium effect [SMD (AB vs. BB) =  - 3.83, 95% CI - 6.41, - 1.24] as compared to cows with AA and BB genotypes, respectively. This finding was confirmed under dominant and completely over dominant models. In case of fat%, AA genotype showed negative effect (SMD =  - 0.51, 95% CI - 0.84, - 0.17) under recessive model. It was concluded that the propagation of allele A is promising to help dairy farmers to improve the genetic quality of their dairy cows.