Effect of BLG gene variants on milk-related traits in small ruminants: a meta-analysis

Abstract

This study aimed to investigate the effect of A and B alleles of beta-lactoglobulin (BLG) gene on milk-related traits in small ruminants by using data reported in 26 potential articles. Records from 9439 genotyped sheep and goats were analysed by utilising four genetic models, including dominant (AA + AB vs BB), recessive (AA vs AB + BB), additive (AA vs BB), and co-dominant (AA + BB vs AB). The effect size of each genotype on daily milk yield, fat percentage, and protein percentage was measured as a standardised mean difference (SMD). The fixed-effects or random-effects model was used to analyse data based on the results of the heterogeneity test. The results showed that B allele of BLG gene positively, but slightly increased the fat percentage of milk in combined data of sheep and goat under dominant (SMD = 0.207, p = .018), recessive (SMD = 0.190, p = .000) and additive (SMD = 0.699, p = .003) genetic models. Also, a statistically significant effect of B allele on daily milk yield of goat was found under dominant (SMD = 0.208, p = .001) and co-dominant (SMD = −0.149, p = .002) models. There was no association between studied alleles and milk protein percentage in sheep and goat. Results of publication bias tests showed a lack of bias and sensitivity analyses suggested additive model as the best one and animals with BB genotype showed highest performance in milk fat production with a SMD equal to 0.699. Highlights Meta-analyses results indicated a small to medium association between BLG variants and daily milk yield in goats The B allele of BLG gene positively affect milk fat percentage in small ruminants The sensitivity analysis suggested additive genetic models for analysing data of fat percentage in small ruminants, based on the absence of outlier studies No association between BLG variants and milk protein was found