Ammonia treatment of wheat straw. 1. Voluntary intake, chewing behaviour, rumen pool size and turnover and partition of digestion along the gastro-intestinal tract of sheep

Intake and digestion and rate of passage kinetics were studied in 6 wether sheep fed on ammoniated wheat straw (AWS) plus pelleted sugarbeet pulp, untreated wheat straw plus sugarbeet pulp, and untreated wheat straw supplemented with urea. Ammonia treatment increased intake and whole tract digestion (rumen + small intestine + large intestine) without significantly affecting rumen pool size and rate of passage. 91% of the increased intake of cell wall material in ammonia-treated straw was due to a higher rate of degradation of cell walls in the rumen. No significant effects of ammonia treatment on concentration, molar composition or rate of absorption of volatile fatty acids were observed. The rate of passage in the large intestine and the contribution of this region to digestion were not significantly affected by ammonia treatment. Rumination and eating time and daily number of rumen contractions did not differ among diets, but AWS showed a lower rumination time/kg NDF ingested than the other 2 diets. After ammonia treatment, whole tract digestion and rumen degradation of hemicellulose increased more than those of cellulose. The effects of ammonia treatment could not be attributed to its nitrogen content since there was no effect on any parameter, except rumen ammonia-N concentration