Effects of Essential Oils and Their Derivatives on Rumen Fermentation Characteristics and PUFA Biohydrogenation: A Meta-Analysis of In Vitro Studies

The present meta-analysis study was aimed to determine effects of essential oil and their derivatives (EOD) supplementation as natural additives on rumen fermentation characteristics and rumen biohydrogenation (BH) activity in vitro. A meta-analysis database was built from the 28 verified scientific articles and further all data were analysed through the continuous random effects model using OpenMEE. It was evaluated that the EOD levels up to 500 mg/L. It showed that high EOD levels increased pH and acetate concentration (P < 0.001) but reduced ammonia, propionate, the acetate to propionate ratio, total volatile fatty acid, and rumen gas production in vitro (P < 0.001). On the perspective of rumen fatty acids profile, the increased EOD levels also positively accumulating n-9 monounsaturated fatty acid, conjugated linoleic acid c9 t11, as well as n-6 and n-3 polyunsaturated fatty acid (PUFA) in the rumen after in vitro fermentation (P < 0.001), and consequently inhibited rumen biohydrogenation (BH) of n-6 and n-3 PUFA (P < 0.001). Meta-regression analysis also showed a negative correlation between EOD supplementation levels and the BH of C18:2 n-6, C18:3 n-3, C20:5 n-3, and C22:6 n-3. It was suggested that the EOD supplementation at 300 mg/L indicated a positive effect on modulating the rumen PUFA metabolism. Above all evidences, it can be concluded that EOD treatment can reduce rumen fermentability but increase the proportion of beneficial fatty acids and inhibit the rate of BH PUFA.