A meta‐analysis on association between CSN3 gene variants and milk yield and composition in cattle

Summary A meta‐analysis on the effects of A and B alleles, the most frequent alleles of CSN3 gene, on milk yield and composition traits was conducted by pooling a large dataset consisting of 30 471 genotyped cattle. Four genetic models, comprising dominant (AA + AB vs. BB), recessive (AA vs. AB + BB), additive (AA vs. BB) and co‐dominant (AA + BB vs. AB), were employed to analyze data. Standardized mean difference (SMD) was used to measure the size of the effects of A and B alleles of CSN3 on studied traits. Effect sizes of 0.2, 0.5 and 0.8 represent small, medium and large effects, respectively. The results indicate that B allele, in the form of BB genotype, has a significant, but medium effect on lactation yield under dominant (SMD = 0.259, P‐value = 0.006) and additive (SMD = 0.279, P‐value = 0.035) models. Moreover, a small decrease in the fat percentage occurred in cows having A allele under dominant (SMD = −0.077, P‐value = 0.006) and additive (SMD = −0.106, P‐value = 0.035) models. Furthermore, CSN3 variants significantly but slightly affect protein percentage under dominant (SMD = −0.146, P‐value = 0.000), recessive (SMD = −0.077, P‐value = 0.000) and additive (SMD = −0.219, P‐value = 0.000) models, showing the negative effect of A allele on this trait. Meta‐analysis results reveal that daily milk yield is slightly affected by CSN3 variants under recessive (SMD = 0.056, P‐value = 0.033) and additive (SMD = 0.061, P‐value = 0.013) genetic models. There is no effect of CSN3 variants on either protein or fat yield. In addition, the effects of CSN3 variants on milk‐related traits were not observed under the co‐dominant model. Sensitivity and publication bias analyses were carried out to confirm the stability of meta‐analyses results.