Digestion, ruminal fermentation and microbial nitrogen supply in sheep fed soybean meal treated with Cistus ladanifer L. tannins

Three rumen-cannulated rams were used in a 3 × 3 Latin square experiment to evaluate the effect of a condensed tannin (CT) extract of Cistus ladanifer L. on apparent digestibility, N balance, rumen microbial N supply, ruminal fermentation characteristics, in sacco rumen degradability and in vitro intestinal digestibility (ivID) of soybean meal. The rams were fed with diets consisting of 600 g of oat straw, 300 g of manioc and 100 g of soybean meal treated with 0, 15 and 30 g/kg of Cistus CT, resulting in three treatments: control (SC), medium (SM) and high condensed tannins (SH).Apparent digestibility of DM, organic matter (OM), crude protein (CP), neutral detergent fibre (NDF), acid detergent fibre (ADF) and gross energy (GE) was similar among experimental diets (P > 0.05). In the rumen, the concentration of NH3-N and microbial N supply in g/day tended to be reduced with the inclusion of CT extract (P = 0.08 and P = 0.06, respectively). The pH and VFA concentrations were not affected by CT. Tannins decreased the effective degradability (P) of soybean meal protein at high levels of feeding, with faster outflow rates (k = 0.08 h−1) (0.53, 0.50 and 0.50 for SC, SM and SH, respectively) (P = 0.02) and the ivID of rumen undegradable protein (RUP) (0.77, 0.74, 0.74 for SC, SM and SH, respectively) (P = 0.04).The utilisation of soybean meal supplemented with 15 g/kg of C. ladanifer condensed tannins can be a valuable approach to reduce the rumen protein effective degradability without compromising the effective dry matter degradability and the digestibility in the whole digestive tract. The reduction of the intestinal digestibility of RUP and of microbial protein synthesis seems to be balanced by an increase in protein absorption in lower digestive tract.