Abstract: The objective of this study was to examine the interaction effect of additions
cattle feed supplement (CFS) with feed concentrate on rumen fermentability and fiber
degradability of low-quality tropical forages. The forage used is Paspalum conjugatum
contain 5.44% of crude protein, feed concentrate contains 7.52% of crude protein and the
CFS is containing 22.07% crude protein and 1.17% condensed tannin. The study was
conducted in vitro using a split plot design with 2 main plots of full forage ration (FF) and
forage + concentrate ration 60: 40% DM basis (FC), each plot was split with 4 levels of
CFS (0, 5, 10 and 15% DM basis). The results showed the interaction effect of CFS
addition and concentrate to crude fiber and fiber fraction degradation (P<0.05), but no interaction on rumen fermentability (P>0.05). The addition of CFS had a linear effect to
increasing the rumen pH (P = 0.01), decreasing the VFA total (P = 0.03), decreasing the
iso-VFA (P = 0.03) and decreasing the ratio of acetate / propionate (P=0.03). Dry matter
degradability increased in CFS 10% (P <0.01), but not significant on organic matter
degradability (P = 0.18). The interaction effect of CFS and concentrate was shown by
decreased degradability of ADF (P = 0.03) and cellulose (P <0.01) in FF ration but an
increase in FC ration and a higher linear increase to degradability of crude fiber, NDF and
hemicellulose in FC than FF ration (P <0.01). The best, the CFS are given with feed
concentrate at the level of 10%.