Meta-analysis of the responses of laying hens to garlic (Allium sativum) supplementation

The potential of phytobiotics, also referred phytogenics or botanical to improve animal productivity has been highlighted. However, consensus has not been reached on the use of garlic, one of such phytobiotics to boost productivity of laying hens. The objectives of this meta-analysis were to assess the effectiveness of supplementation with garlic on feed intake (FI), feed conversion ratio (FCR), hen day egg production (HDEP) and egg quality attributes of lay hens. Databases [Scopus, Google scholar, and Access to Global Online Research in Agriculture (AGORA)] were searched for peer-reviewed randomized controlled trials (RCTs) published in English. Criteria for inclusion in the meta-analysis were information on moderators (breed, preparation form of garlic, treatment duration, age of hen at the beginning of garlic intervention, country where the study was performed, number of chickens included in the study, inclusion level of garlic), an adequate description of randomization, egg production and egg quality data, and associated measures of variance such as standard deviation (SD), standard error (SE) and P - values. Nineteen (19) out of 53 research papers met the criteria for inclusion in the meta-analysis. All analyses were conducted using the Open Meta-analyst for Ecology and Evolution (OpenMEE) software. Overall pooled results revealed that garlic supplementation increased HDEP by 0.322% [95% confidence interval (CI) = 0.211 to 0.432], egg mass by 0.486 g/day/hen [95% CI = 0.163 to 0.810], egg weight by 0.069 g [95% CI = 0.001 to 0.136], egg shell thickness by 0.259 mm [95% CI = 0.160 to 0.358] and egg shell weight by 0.219 g [95% CI = 0.087 to 0.350] relative to controls, taking cognizance of publication bias and heterogeneity. Chickens fed diets with or without garlic had comparable FCR. Results suggest that there was no evidence of treatment effect on FI and Haugh unit. Subgroup analysis found that studies that used garlic extract had significant egg weight while studies that used garlic powder and oil had similar egg weight. Meta-regression analysis showed that study country, breed, hen?s age, garlic preparation form, inclusion level of garlic, number of hens included in the study and treatment duration were predictors of the study effect. The results of