The effects of garlic as a feed additive on ruminal fermentability and ruminant performance: A meta-analysis

Garlic exhibits antimicrobial activity and it may serve as a feed additive for ruminants, yet quantitative summaries of its effects are lacking. Therefore, the current study evaluated the addition of various garlic products as feed additives on ruminal fermentability and ruminant performance using a meta-analysis method. The database was compiled from 37 articles with 157 comparison studies in Scopus and PubMed. The data sets were analysed using a random-effects model in OpenMEE software and the bias publication was evaluated by using Jeffreys's Amazing Statistics Program (JASP) software. The results revealed that garlic significantly increased the percentage of propionate, butyrate, valerate and iso-butyrate, as well as the total number of rumen bacteria, dry matter intake, crude protein intake and ruminant average daily gain (p < 0.05). In contradiction, garlic addition in ruminant feeds led to decreases in methane production, percentage of acetate, the ratio of acetate to propionate, in vitro neutral detergent fibre digestibility and the total number of protozoa (p < 0.05). The subgroup analysis indicated that garlic oil, garlic powder and garlic bulb decreased methane emissions, while garlic powder and garlic bulb raised the percentage of propionate. In conclusion, garlic products altered the percentage of total volatile fatty acids and total number of rumen microflora, while increasing the feed intake and body weight gain. Thus, garlic products could be used as a dietary additive to support sustainable ruminant animal production. • The meta-analysis indicates that incorporating garlic as a ruminant feed additive reduces methane emissions. • Due to reduced methane gas production, the average daily gain in ruminant has increase. • Garlic oil, garlic powder and garlic bulb have been observed to decrease methane gas production in the rumen. • Both garlic powder and garlic bulb enhance the propionate percentage, a precursor for meat formation in ruminants.