Effect of Acacia mearnsii as a source of tannins on rumen fermentation in vivo and gas production kinetics in vitro

This study investigated the effect of Acacia mearnsii forage (AMF) inclusions in maize silage on the rumen volatile fatty acids (VFAs) (acetic, propionic and butyric acid); and AMF inclusions in maize silage and A. mearnsii tannin extract (ATE) in pellets on in vitro gas production kinetics. To determine the VFA profile, twenty-four crossbred (Holstein-Friesian and Jersey) cows were equally assigned to four treatments; 0, 5, 15 or 25 % (as fed) AMF in maize silage in a completely randomized study design. Cows were subjected to 14 d adaptation period to treatments then 21 d of weekly rumen fluid sampling per treatment followed. The above-mentioned treatments were assessed for their effect on the in vitro gas production kinetics along with 0, 0.75 , 1.5 or 3 % (as fed) ATE inclusion in concentrate pellets and incubated for 0, 2, 4, 6, 8, 12, 24, 36, 48, 72 and 96 h. Dietary AMF inclusions did not affect (P>0.05) total rumen volatile fatty acids but linearly increased (P<0.05) propionic and butyric acid. Similarly, it did not change (P>0.05) the in vitro gas production kinetics, while ATE decreased the gas production rate linearly (P<0.05). In conclusion, AMF and ATE slightly affected rumen fermentation since AMF inclusions increased propionic and butyric acid linearly up to the 25% inclusion while ATE inclusions decreased the gas production rate.