A Meta-analysis of Responses of Broiler Chickens to Dietary Zinc Supplementation: Feed Intake, Feed Conversion Ratio and Average Daily Gain.

The importance of zinc (Zn) in broiler chicken nutrition is gaining attention due to the realization of its role in several enzymes and metabolic functions. This meta-analysis, therefore, aimed to synthesize pooled evidence on the effectiveness of Zn supplementation on enhancing feed intake, feed conversion ratio (FCR) and average daily gain (ADG) in broiler chickens. Thirty-seven peer-reviewed studies out of 436 identified from the search carried out in Scopus, Google Scholar and PubMed databases met the criteria for inclusion in this meta-analysis. Data were pooled and then disaggregated for moderators: broiler strains, sources of Zn, duration of Zn supplementation and Zn supplementation levels. All the analyses were conducted in Open Meta-analyst for Ecology and Evolution (OpenMEE) software. Pooled results indicate that Zn supplementation increased feed intake [standardised mean differences (SMD) = 0.34 g/bird/day; 95% confidence interval (CI) 0.27, 0.42)] and ADG (SMD = 0.43 g/bird/day; 95% CI 0.35, 0.50) in broiler chickens in comparison with the controls. Dietary Zn supplementation improves FCR (SMD =  - 0.16 g/g; 95% CI 0.20, - 0.11), taking heterogeneity and publication biases into account. Restricted subanalysis showed that studied moderators influenced the outcomes of the meta-analysis. Meta-regression revealed that moderators explain about 38% of the sources of variations in the present study. This meta-analysis suggests that dietary zinc supplementation had a positive effect on growth performance indices in broiler chickens.