Intake, digestibility and nutrients supply to wethers fed ryegrass and intraruminally infused with levels of Acacia mearnsii tannin extract

Four Polwarth × Texel wethers (30 ± 1.8 kg body weight), fitted with a chronic rumen catheter and duodenal cannulae, housed in metabolic cages and offered ryegrass (Lolium multiflorum Lam) ad libitum were used in a 4 × 4 Latin Square experiment to evaluate the effects of infusing Acacia mearnsii tannin extract on intake, digestion and nutrients supply. Treatments consisted of no tannin (0) or intraruminal infusion of a tannin extract solution in a final volume that allowed for a tannin extract concentration of 20, 40 or 60 g/kg of dry matter (DM) intake. Intake and total digestibility of organic matter (OM), neutral detergent fiber (NDF) and N compounds linearly reduced (P ≤ 0.05) at increased levels of tannin infusion. Urinary N excretion linearly decreased (P ≤ 0.05) whereas the proportion of ingested N, which was retained was not affected by treatments. Duodenal flow of -amino N was not affected by treatments whereas rumen microbial N entering the duodenum tended to linearly decreased (P = 0.15) at increased levels of tannin infusion. Ruminal degradability of both OM and dietary N compounds linearly decreased (P < 0.05) at increased levels of tannins. The efficiency of rumen microbial protein synthesis was not affected by treatments. In conclusion, the use of Acacia mearnsii tannin extract as feed supplement for wethers fed ryegrass, at rates from 20 to 60 g/kg DM intake, does not affect the -amino N supply at the duodenum whereas it shows a negative impact on energy intake.