Medium-chain fatty acids from coconut or krabok oil inhibit in vitro rumen methanogenesis and conversion of non-conjugated dienoic biohydrogenation intermediates

Myristic (C14:0) and lauric (C12:0) acid have been suggested to synergistically influence rumen methanogenesis. This experiment compared the effect of krabok and coconut oil on rumen fermentation, in an attempt to assess this synergism using two natural oil sources which contain similar amounts of C12:0 but with krabok oil containing greater proportions of C14:0 than coconut oil. As a simultaneous action on both rumen methanogenesis and biohydrogenation has been reported for another medium chain fatty acid (C10:0), rumen biohydrogenation also was monitored during the current in vitro study. Five treatments were used: one control (CON), without supplementation of coconut or krabok oil, two coconut oil and two krabok oil supplemented incubations. Coconut and krabok oil were supplemented in two doses, providing either 80 (C80 and K80) or 120 mg (C120 and K120) of C12:0 + C14:0 per 100 ml of incubation fluid. A standard concentrate typically fed to ruminant livestock in Thailand (200 mg), buffer (20 ml) and rumen fluid (5 ml) were added to each incubation flask, with or without an external PUFA source (20 mg of a mixture of sunflower and linseed oil). All flasks were incubated at 39 °C for 24 h. Both krabok and coconut oil reduced methane production (P<0.05) and increased propionate production (P<0.05) at the expense of acetate (P<0.05) and butyrate production (P<0.05). Krabok and coconut oil induced similar changes and effects were stronger in combination with linseed and sunflower oil, whereas the latter, in the amounts supplemented here, did not change methane production nor induced shifts in the production of any of the VFA. A trend for lower amounts of C18:2 n-6 and C18:3 n-3 after 24 h incubation was observed indicating a higher rate of lipolysis and isomerization of C18:2 n-6 and C18:3 n-3, as the inclusion levels of krabok oil increased. Overall, the effect of krabok and coconut oil on rumen biohydrogenation was limited.