Meta-analysis of MspI derived variants of growth hormone gene associated with milk yield in dairy cattle

Objective

The present work aimed to obtain common effect sizes for the gene frequency and association of MspI derived variants of growth hormone (GH) gene with milk yield in dairy cows.

Methods

We performed a systematic review and meta-analysis of 35 published studies identified in literature search from 2000 to 2020 (n = 4164). These studies were specific to fragment size (329) for genotypes viz., CC (224, 105 bp), CD (329, 224, 105 bp) and DD (329 bp). Pooled standard mean differences (SMDs) as effect sizes between allele pairs were derived using different genetic models. The heterogeneity between effects sizes across studies was estimated using I² Index (%).

Results

The common effect size for gene frequency of allele C (224, 105 bp) was significantly (P < 0.05) higher in 2881 Bos taurus/cross cows (0.82; 95% CI: 0.74, 0.89; I² = 97.81%) than 1283 Bos indicus cows (0.15; 95% CI: 0.12, 0.18; I² = 71.90%), with overall gene frequency was 0.33 (95% CI: 0.21, 0.46; I² = 99.29%). Additive (CC vs. DD) and dominant (CC + CD vs. DD) did not revealed significant (P > 0.05) association with milk yield. However, completely over dominant (CC + DD vs. CD) and recessive (CC vs. CD + DD) models showed significant (P < 0.05) and positive SMDs with milk yield specially at early lactations. There was no evidence of heterogeneity (I² = 0.00%) between SMDs across studies.

Conclusions

This meta-analysis suggested potential association of C allele for enhancing milk production of dairy cows.