Meta-analysis of garlic in small ruminant nutrition: dry matter intake, rumen fermentability, nutrient digestibility, and blood biochemical indices

Context The effects of garlic (Allium sativum L) intervention on ruminant productivity have been studied with inconsistent results, thus making it hard to utilize this data in decision-support systems in the ruminant industry. Aim This meta-analysis assessed the effectiveness of garlic in improving dry matter intake (DMI), rumen fermentability, nutrient digestibility, blood biochemical indices, and reducing methane emissions in small ruminants. Methods Nineteen (19) articles were identified via systematic searches performed in PubMed, Web of Science, Google Scholar, and Scopus databases. The Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines were used for the analysis. Data was pooled using the random-effects model, and results were expressed as mean differences (MD) at a 95% confidence interval. Subgroup analyses were conducted to explore the impact of small ruminant types (sheep versus goats) on response variables. Mixed-effect meta-regression analysis was performed to quantify the impact of moderators [breeds, body weight (BW) at the beginning of the study, duration of garlic intervention, sex, diet types, small ruminant types, and dosage] on the observed heterogeneity on volatile fatty acid (VFA). Heterogeneity and publication bias were assessed using standard methods. Key results The pooled result indicates that garlic increased the concentrations of ruminal VFA (P = 0.039), acetate (P < 0.001), and propionate (P < 0.001), and decreased methane emissions (P < 0.001). The results show that garlic increased the digestibility of dry matter (DM) (P = 0.008), ether extract (EE) (P = 0.001), crude fiber (CF) (P < 0.001), and neutral detergent fiber (NDF) (P = 0.002). Pooled estimates also revealed that garlic decreased concentrations of blood cholesterol (P = 0.004) and low-density lipoprotein (LDL) (P < 0.001). Subgroup analysis showed that small ruminant types influenced the results of the meta-analysis. Meta-regression showed that small ruminant types, breeds, diet types, and BW were the drivers of inconsistent results in small ruminants on garlic intervention. Egger’s regression asymmetry test showed the absence of publication bias, indicating that the results were valid and reliable. Conclusion This meta-analysis highlights the potential of garlic intervention in small ruminants to enhance the digestibility of DM, EE, CF, and NDF, increase the levels of ruminal VFA, acetate, and propionate, and decrease blood cholesterol, LDL, and ruminal methane emissions. Implications The current study sets guidelines for standardized experimental designs on the use of garlic in ruminant nutrition in the future.