Dietary factors influencing the digestion of starch in the rumen and small and large intestine of early weaned lambs.

I . Lambs fitted with cannulas in the abomasum, terminal ileum and caecum were used to study the digestion of starch and dry matter when rations with high starch content were given. Polyethylene glycol was used as an indigestible reference substance. 2. In Expt I reduction in level of feeding from an estimated ad lib. intake to 70% of this level reduced the amount of dietary starch escaping fermentation in the rumen from 6.8 to 4.4 % of intake on a barley diet and from 12.8 to 7.7 % on a diet consisting of 40 % dried grass and 60 yo barley. Inclusion of 40% chopped dried grass in the diet increased the amount of dietary starch escaping fermentation in the rumen. There appeared to be a linear relationship between the concentrations of starch in abornasal and ilcal dry matter, indicating a limited capacity for starch digestion in the small intestine. 3. In Expt 2 a barley diet was compared with diets based on flaked maize, ground maize or cracked maize. With these diets the percentage of dietary starch escaping fermentation in the rumen was respectively 6.2, 5.4, 12.1 and 142, showing that more starch escapes fermentation with uncooked maize diets than with barley diets. 4. The molar proportions of volatile fatty acids produced by fermentation in the caecum were apparently influenced by the amount of starch passing to the intestines. The highest proportion of acetic acid (78 %) was associated with 4.5 % of starch in abomasal dry matter, and the lowest proportion (57 yo) was associated with 20.1 % of starch in abomasal dry matter. 5. The possible relationships between the extent of fermentation in the rumen and energy and nitrogen metabolism are discussed.