Effects of Acacia mearnsii De Wild. extract and monensin on intake, digestibility, and ruminal variables of lambs

This study evaluated the effects of tannin extract of Acacia mearnsii De Wild. or monensin on intake, digestibility, nitrogen balance, and ruminal variables of lambs. Five rumen cannulated lambs (40.3 +/- 2.8 kg) were used in a 5 x 5 Latin square design, with periods of 21 days each. The treatments were: control, without additive; Tan-0.60, Tan-1.20, and Tan-1.80 for the doses of 0.60, 1.20, and 1.80 g kg-1 body weight (BW) of tannin extract, respectively; and ionophore (monensin) at 0.75 mg kg-1 of BW. Tannins reduced the digestibility of dry matter (DM) and the greatest effects were observed for Tan-1.80. Tannins also increased or tended to increase the fecal excretion of DM, and the greatest effects were observed for Tan-1.20 and Tan-1.80. Tannins increased the fecal excretion of N, decreased the amount of N in urine, but did not affect N retained. Furthermore, tannins reduced the concentration of valerate and the acetate:propionate ratio and increased propionate without affecting the amount of total volatile fatty acids, and the greatest effects were observed for Tan-1.80. The use of ionophore only increased the elimination of N in the urine. Thus, monensin does not affect nitrogen retention, and tannin impairs digestibility, but increases propionate production.