Impact of a tannin extract on digestibility and net flux of metabolites across splanchnic tissues of sheep

This study was conducted to quantify the impact of the dietary inclusion of Acacia mearnsii bark extract (TA), a tannin extract, on total tract digestibility and on ammonia, urea and glucose splanchnic net flux in sheep. The trial was conducted with five Texel male sheep (48 +/- 3.2 kg body weight (BW)) surgically implanted with chronic indwelling catheters into one mesenteric, portal and hepatic veins, in two 21-day periods, in a cross-over design. Diet was oat/ryegrass hay, offered ad libitum, plus concentrate offered three times per day at a rate of 14 g/kg BW. The concentrate, composed of soybean meal, cracked corn and wheat bran, included (Tannin) or not (Control) 20 g/kg dry matter (DM) of TA. Plasma flow and net flux through portal-drained viscera (PDV), liver and total splanchnic tissues (ST) were measured using four hourly samples, from 14:00 to 17:00, after the 12:00 meal. Total TA concentration in diet of TA treatment averaged 7.7 g/kg DM. The organic matter (OM) intake and digestibility were not affected by TA. The nitrogen (N) intake and fecal excretion, the estimated rumen microbial N flow to the small intestine and the efficiency of microbial protein synthesis (EMPS) were not affected whereas the digestibility of N compounds and the urinary excretion of urea-N were lower (P < 0.05) in TA treatment. There was no significant effect of TA on the net flux of ammonia, urea-N or glucose across PDV, liver and total ST. In conclusion, the dietary inclusion of tannin extract from Acacia meanrsii at a rate of 7.7 g/kg DM decreased the urinary excretion of urea with, however, no impact on ammonia, urea or glucose net flux across ST.