Changes in rumen fluid composition and in the rumen epithelium when wheat is introduced to the diet of sheep: the influence of wheat and hay consumption

Abstract

The effects of the levels of wheat and of hammermilled hay fed to sheep on ruinen acidity and ammonia concentration were determined during the first 4 days of feeding wheat. Consumption of wheat reduced rumen pH, but the effect diminished with time, so that by day 4 it was not significant. Wheat intake also significantly (P < 0.05) increased rumen ammonia on day 1, but not during days 2-4. Volatile fatty acid (VFA) concentrations on day I were increased (P < 0.05) by wheat intake, the effect being less on later days. The proportion of acetate was reduced (all days). while propionate (days 1, 2 and 4) and butyrate (days 3 and 4) were increased by the consumption of wheat. Concentrations of lactate (mainly the D-isomer) increased after wheat was fed, although wheat level per se did not significantly affect lactate concentrations. Peak concentrations of lactate occurred on day 2 (18 m~ total lactate). Initially, consumption of hay decreased rumen pH and had little effect on ruman ammonia levels. By day 4, hay consumption was associated with increases in rumen pH and decreases in rumen ammonia levels (0.006 units and -0.05 mM per g hay dry matter (DM) respectively). Concentrations of VFA tended to be increased by hay consumption, but the proportions of the major VFAs were not affected. Hay intakes on day 4 were associated with reductions in rumen total lactate concentrations of 51 ¦M per g hay DM. Reduced total DM intakes of sheep eating ad libitum were associated with low rumen pH and high lactate concentrations. Microscopic lesions were observed on the rumen papillae of sheep 7 days after wheat was first fed. The extent of these lesions was reduced by hay intake, and was also related to the minimum pH observed.