In situ disappearance of individual proteins and nitrogen from legume forages containing varying amounts of tannins

In situ degradability of N and proteins were studied in one cultivar of alfalfa and red clover and two cultivars each of birdsfoot trefoil and sericea lespedeza. Concentrations of tannic acid equivalents (percentage of DM) were 0.68 in one cultivar of birdsfoot trefoil and 1.77 and 2.78 in the two cultivars of lespedeza. The other forages contained essentially no tannins. Forage samples were digested in situ for 0, 2, 4, 6, and 12 h. The amount of N remaining at 12 h was positively correlated with concentrations of tannin. About 38% of the N remained after 12 h in forages with no or low concentrations of tannins, and 86% remained in the two cultivars of lespedeza. Total electrophoretically identified proteins followed similar trends, but the percentage remaining was less than that for N. For all forages, bands were found at molecular masses of 15, 30, 45, 47, and 54 kDa. The percentage of 54-kDa protein that remained after 12 h was less than that for the other four proteins (23% vs. 37%). No interaction was found between forage cultivar and protein species. These results showed that tannins reduced ruminal degradation of proteins and that specific forage proteins degraded at different rates that were independent of tannin concentration.