An in vitro study on the ability of tannic acid to inhibit methanogenesis and biohydrogenation of C18 PUFA in the rumen of goats

An in vitro gas production technique, using rumen fluid from four Kacang × Boer crossbred adult goats was used to study the effects of commercial tannic acid (TA, a hydrolysable tannin) on methanogenesis, fatty acid composition and biohydrogenation (BH) of C18 polyunsaturated fatty acids (PUFA) in the rumen. Treatments were control (CON, 50% alfalfa hay (AH) + 50% concentrate), 25 mg TA/250 mgDM (LTA, low TA) and 50 mg TA/250 mgDM (HTA, High TA), which were mixed with 30 mL of buffered rumen fluid and incubated for 24 h. The study revealed that TA supplementation had no negative effect on rumen fermentation parameters such as pH, NH₃N, acetic/propionic ratio and total volatile fatty acid (tVFA). Methane (CH₄) production (mL/250 mg DM) decreased (P<0.05) with increasing levels of TA. Greatest CH₄ reduction (%) was recorded for MTA (20.30%) and LTA (13.00%) compared with CON. Supplementation of the diet with TA did not affect the rate of rumen BH (%) of C18:1n-9 (oleic acid; OA), C18:2n-6 (linoleic acid; LA), C18:3n-3 (linolenic acid; LNA) and the concentration of fatty acids after 24 h of in vitro incubation. Based on this study, the addition of TA in vitro reduced rumen methanogenesis without negative effect of rumen fermentation characteristics, but in vivo studies need to be performed to determine if concentrations that inhibit methane are below toxic levels.