Comparative aspects of digestion of four roughages by sheep

Abstract

Movement of digesta through the reticulorumen and through the intestines has been studied for four roughage diets (wheaten straw, ws; wheaten hay, WH; lucerne hay, LH; dried subterranean clover, sc; all in chopped form) given to sheep fitted with re-entrant duodenal cannulas. The extent and tbe sites of digestion of plant organic matter and its constituent soluble sugars, polysaccharides, pectin, and protein are described for the four roughages. Sugars, water-soluble polysaccharides and pectin were completely digested on all diets, almost entirely in the stomachs. Together these fractions contributed 16, 21, 25 and 27% of the apparently digested organic matter respectively for ws, WH, LH and sc diets. The digestibility of hemicellulose ranged from 49.5% (WH) to 80.9% (sc); of the hemicellulose digestcd, from 70% (WH) to 81 % (sc) was apparently fermented in the reticulorumen. The digestibility of cellulose ranged from 58 % (WH) to 88 % (sc), and of the cellulose digested, 83 % (WH) to 89 % (sc) was apparently fermented in the reticulorumen. Together, apparently fermented cellulose and hemicellulose contributed from 25 %: (sc, LH) to 55 % (ws) of apparently digested organic matter. Despite evidence of nitrogen loss across the reticulorumen on thee two high nitrogen diets (LH, - 10 %; sc, - 22 %) and net gains in nitrogen on the two lower nitrogen diets (ws, + 50 %; WH, +20%), the yield of all amino acids at the duodenum per 100 g digestible organic matter intake was about 50 % higher for LH and sc (which were similar) than for ws and WH (which were similar). The relative proportions of essential amino acids did not change significantly. Nutritional implications of these changes in the site of digestion and of the proportions of nutrients released to the animal are discussed.