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

Abstract

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.

Intake, digestion and small intestinal protein availability in sheep in relation to ammoniation of wheat straw with or without protein supplementation

“…Straw, chopped to a length of approximately 50 mm, was fed ad lib, by offering at least 25 % excess. Ammoniation of the wheat straw was done as described by Oosting et al (1993~).…”

“…These samples were freeze-dried, ground and pooled for each sheep, week and cannula and subsequently analysed for DM, ash, Co, Cr, cell-wall composition, N and AA. As in the experiment described by Van Bruchem et al (1993) with sheep fed on UWS and AWS, duodenal and ileal samples were representative in respect of fluid and particulate phases : the Cr: Co ratio introduced into the rumen was on average 1.19. In duodenal samples this ratio was 1.21 (~~~0 .…”

“…The equation for estimation of the small-intestine true digestion as given previously was derived from the equation used by Van Bruchem et al (1989). The latter equation to estimate endogenous AA output and true AA digestion in the small intestine had the following form :…”

“…absorption from the small intestine depends on the amounts of AA entering the duodenum, either from feed or of microbial origin, the amounts of endogenous protein added to the digesta, the true digestibility of the feed and microbial protein, and the proportion of endogenous protein that passes from the ileum to the caecumsolon (Van Bruchem et al 1989). Limited rumen availability of nutrients such as peptides, branched-chain volatile fatty acids (VFA) and/or minerals in combination with a long retention time of microbes in the rumen may be reasons for the relatively low efficiency of microbial protein synthesis (Hespell & Bryant, 1979;Hoover, 1986), as found for untreated and ammoniated wheat straw (Oosting et al 1993b).…”

“…Limited rumen availability of nutrients such as peptides, branched-chain volatile fatty acids (VFA) and/or minerals in combination with a long retention time of microbes in the rumen may be reasons for the relatively low efficiency of microbial protein synthesis (Hespell & Bryant, 1979;Hoover, 1986), as found for untreated and ammoniated wheat straw (Oosting et al 1993b). However, ileal endogenous AA losses were lower for rations based on untreated and ammoniated wheat straw (Oosting et al 1993b) than for rations based on forages grown under temperate conditions (Van Bruchem et al 1989). Hence, major constraints to AA availability in the small intestine for rations with straw as the major component are the low efficiency of microbial protein synthesis in the rumen in combination with a low flow of AA derived from straw, which probably have a low smallintestinal digestibility (Hvelplund, 1989).…”