Effect of chelated zinc on milk production in dairy cows: Meta-analysis

In this review, a systematic meta-analysis on randomized controlled trials that evaluate the effectiveness of supplementation of chelated zinc (Zn) on milk production in dairy cow has been performed. A total of 2106 transition dairy cows belonging to 23 studies from 7 papers were finally selected (treated, n = 1053; control, n = 1053). A meta-analysis of the effect of chelated Zn on milk production in dairy cow during lactation period was conducted following a search of literature. The data of cows either treated or controlled were extracted and analyzed by using comprehensive meta-analysis software program. I 2 statistic was used to estimate the degree of heterogeneity. Forest plot was used to present the means and their confidence intervals in a graphic manner and heterogeneous degree were explored with meta-regression; also, Begg’s test was conducted to investigate the publication bias. Overall, trial analysis of trials revealed that there was no significant effect of chelated Zn on milk production based on effect size (ES) and the confidence interval (95% CI) in comparison with the control cows (milk production ES = (0.941–1.183) 1.057, p value =0.337). A forest plot for the impact of chelated Zn on milk production was presented. The forest plots indicated that there is no heterogeneity between treated and control cows in response to supplementation of chelated Zn on milk production. The results of Begg’s test for publication bias were not significant. In conclusion, chelated Zn supplementation among dairy cows during lactation period provided a non-significant impact on milk yield.