A meta-analysis for association between DGAT1 and Leptin genes polymorphisms with some milk production traits in dairy cows

Meta-analysis is a statistical approach for combining the results from independent studies with the same assumptions, that is able to increase the statistical analysis power and the repeatability of the results in the livestock researches, comparing to single-study analysis. The polymorphism in the major genes of Diacylglycerol O-Acyltransferase 1 (DGAT1) and Leptin have drawn much attention from animal scientists during recent years, for their possible roles in the economically important traits. However, the relationships between these genes and milk production traits have been incompatible in dairy cows, it means sometimes significant and some other times no significant association has been reported. The purpose of this study was to investigate the overall effect of DGAT1 and Leptin genes on some economically important traits including milk yield, fat and protein content and percentages in dairy cows by using meta-analysis.

in this study, all researches published in the validated journals and thesis up to 2018 were used. Following to quality control, 9 and 4 studies reported for K232A and Sau3AI polymorphisms of DGAT1 and Leptin genes were used, respectively. The analysis was carried out using the Stata v. 15. Non conformance index (I 2) was significant for all parameters, so that a random risk model was used. Data were analyzed for each variable using these models for measuring the effect size, 95% confidence interval and statistical significance level of the measurements. All variables were continuously in this study. The measurement of the effect size for continuous data was carried out using the standardized mean difference (SMD) that calculated for the polymorphisms of K232A and Sau3AI loci in DGAT1 and Leptin genes on the milk yield, fat and protein content and percentage.

the results of this study showed that the polymorphism in the K223A locus of DGAT1 gene, has a significant effect on lipid content and percentage, and can play an important role in increasing of their amounts, but its relationship with milk yield and protein content and percentage is not significant. Also, the results for Sau3AI polymorphism in the Leptin revealed that this locus had no significant effect on the traits investigated in this study.

Overall, the results of this study with identifying the overall effects of the studied genotypes of DGAT1 and Leptin genes on milk production traits in dairy cows can play an important role for planning next researches in this field.