Twelve steers fistulated in the rumen and duodenum were allocated to one of three diets and fed 80 g DM/kg W0.75/d. The diets consisted of about 80% maize meal, 11% cottonseed hulls and either 1.44% urea (Treatment A), 0.96% urea (Treatment B) or 0.47% urea plus 5.6% fish-meal (Treatment C) as protein supplements. Passage and apparent digestion of protein and starch in the digestive tract were studied using Co-EDTA and Na-dichromate as fluid and particulate markers, respectively. A higher (P ≤ 0.05) proportion of the dietary protein and starch was apparently digested post-duodenally in steers on Treatment C than in steers on Treatments A and B. Also, duodenal lysine flow was greatest with Treatment C. It is suggested that the supply of amino acids to the small intestine may be inadequate on diets with a UDP content of less than 35 to 40% of crude protein (Treatment C).
