Effect of <i>Acacia mearnsii</i> forage or tannin extract on rumen dry matter and crude protein degradation

This study investigated rumen degradation kinetics of dry matter (DM) and crude protein (CP) in compound feed with different tannin extract inclusions and Acacia mearnsi forage (AMF) relative to dairy feeds (perennial ryegrass+white clover mixture pasture, maize silage, lucerne hay and Themeda triandra hay). The compound feed had 0.75%, 1.5% and 3% tannins extract inclusions while the control was a commercial compound feed. Triplicates of each feed per incubation period were incubated in two fistulated Jersey cows for 0, 6, 24, 48, 72, 96 and 120 h, resulting in six replicates per feed. Tannin extract inclusions in compound feed only affected (p < 0.05) the (a) fraction, degradation rate and potential degradability (PD) for DM degradation, and affected (p < 0.05) the (a) and (b) fractions, as well as PD for CP degradation. The (a) fraction and degradation rate for DM degradation changed linearly (p < 0.05). The (a) fraction, PD and effective degradability (ED) of DM degradation changed quadratically (p < 0.05). Except for the degradation rate, the feed type affected (p < 0.05) the degradation parameters in both DM and CP degradations. For DM and CP degradations, (a) fraction was similarly the least in Themeda triandra hay and AMF but similarly the highest in maize silage, perennial ryegrass+white clover mixture pasture and lucerne hay. The (b) fraction was the least in AMF for both DM and CP degradations but the highest for pasture's DM degradation and similarly the highest in maize silage, lucerne hay and T. triandra hay for CP degradation. The PD was the least in AMF for both DM and CP degradations and similarly the highest in pasture DM but similarly the highest in perennial ryegrass+white clover mixture pasture, maize silage and lucerne hay for CP degradation. Furthermore, the ED was the lowest in AMF and the highest for perrenial ryegrass + white clover mixture pasture for DM degradation and same trend was observed for CP degradation whereby perrenial ryegrass + white clover mixture pasture, maize silage and lucerne had the highest ED. Digestible undegraded protein was the highest in AMF and similarly the least in dairy feeds. Tannin source inclusion in ruminant diets should be moderate to prevent rumen DM or CP degradation limitation.