Effect of ammonia treatment and carbohydrate supplementation on the intake and digestibility of barley straw diets by sheep

The changes in straw voluntary intake and apparent digestibility caused by the ammoniation of straw and energy supplementation in diets fed to adult, non-productive sheep were studied in two experiments. In Experiment 1, untreated (US) or ammonia treated (TS) barley straw were given as the only feed to four ewes in a cross-over design. Ammoniation increased straw dry matter (DM) intake from 30.2 to 50.6 g kg−1 LW0.75, organic matter digestibility (OMD) from 0.438 to 0.519 and digestible organic matter intake (DOMI) from 12.5 to 24.7 g kg−1 LW0.75, allowing energy maintenance requirements to be met. In Experiment 2, three groups of four ewes received US, with another three groups of four receiving TS, both supplemented with meadow grass hay (H), rolled barley (B) or sugar-beet pulp (P) in a 2 × 3 factorial design. Each supplement was given in amounts of 150, 300, 450 and 600 g day−1, in a Latin-square design. The type of supplement did not significantly affect straw intake at any level of inclusion. The level of supplementation scarcely affected US intake, whereas DM intake of TS diminished linearly. Substitution rates were 0.49 ± 0.088, 0.61 ± 0.085 and 0.55 ± 0.131 for TS-H, TS-B and TS-P diets, respectively (P > 0.05). Apparent digestibility of straw was not significantly affected by supplementation. Increases in total DOMI when the level of supplementation was augmented were lower in TS than in US diets, and with H than with B or P as supplements. To reach the DOMI obtained with TS as the only feed, US has to be supplemented with 420, 272 or 269 g DM of H, B or P, respectively.