Tannins in tree legumes: Effects on growth, intake digestibility and nitrogen utilization in Indonesian lambs

The effect of phenolic compounds and proanthocyanidins present in three tree legumes, Paraserianthes falcatoria, Calliandra calothyrsus and Gliricidia sepium, upon growth, intake and diet utilization were evaluated. Tree leaves were evaluated when fed as a supplement to a concentrate basal diet at 25 and 50% of dietary crude protein (15 and 30% of dry matter intake) and, along with the grass Brachiaria brizantha and the herbaceous dicot Asystasia intrusa, when fed alone.; Calliandra calothyrsus had the highest concentrations of soluble phenolics (SPHE), 37.8%, and soluble proanthocyanidins (SPRO), 13.7 absorbance units per gram dry matter (AU/g). Gliricidia sepium had 4.2 to 4.9% SPHE and 0.1 to 0.3 AU/g SPRO with Paraserianthes falcataria having intermediate levels of 4.9 to 15.2% SPHE and 1.4 to 4.8 AU/g SPRO. Insoluble proanthocyanidins were highest in G. sepium.; Supplementing tree legumes to a concentrate basal diet resulted in decreased average daily gain and lower dry matter (DM) and nitrogen (N) digestibilities than the control diet of concentrate supplemented with B. brizantha. Increasing tree legumes from 25 to 50% of dietary crude protein resulted in further decreases in apparent and true N digestibilities and increased fecal output of neutral detergent fiber bound nitrogen (NDF-N). Calliandra calothyrsus supplementation resulted in lower digestibilities of N and DM than supplementation of either P. falcataria or G. sepium.; When fed alone, tree legume fed lambs showed lower DM, NDF and N digestibilities than both B. brizantha and A. intrusa fed lambs. Calliandra calothyrsus exhibited lower apparent digestibilities of DM, NDF, and N than both P. falcataria and G. sepium. Calliandra calothyrsus also showed the lowest intake, 2.0% of body weight, and lowest true N digestibility of 56.8%.; The main action of proanthocyanidins in these tree species was to irreversibly bind protein rendering it less available for microbial and enzymatic degradation and digestion. Calliandra calothyrsus, having the highest SPHE and SPRO concentrations, was most affected as evidenced by the highest fecal NDF-N output and lowest N digestibilities of the three tree species.