Quantitative intestinal digestion of nitrogen in sheep given formaldehyde-treated and untreated casein supplements.

I. In two experiments, sheep prepared with a rumen cannula and with re-entrant cannulas in the duodenum and ileum were continuously fed on diets of dried grass, dried grass plus formalin-treated casein, or dried grass plus untreated casein. Paper impregnated with chromic oxide was given once daily via the rumen fistula. 2. In ten 24 h collections of digesta entering the duodenum and eleven 24 h collections of digesta reaching the ileum of sheep given dried grass, there were highly significant correlations between the 24 h flows of Cr marker and the corresponding flows of dry matter, organic matter, nitrogen, gross energy, hemicellulose and cellulose (P < 0.01) at both sites. 3. Daily amounts of non-ammonia N and of individual amino acids entering and leaving the small intestine and of total Iv excreted in faeces and urine are given. 4. Net retention of supplementary N was 36 % when the supplement was administered as formalin-treated casein, but only 17 % when it was administered as untreated casein. 5. Formalin treatment of casein significantly increased the daily amounts of non-ammonia N entering the small intestine (P < 0.01) and the amounts of non-ammonia N apparently absorbed therein ( P < 0.05). 6. Apparent absorption of amino acids from the small intestine was significantly greater (P < 0.05) with treated casein than with untreated casein. There were relative increases in the small amounts of several free amino acids measured, including taurine, in the ileal digesta of sheep receiving the treated casein supplement.