The rumen degradability of protein in diets containing maize straw, fish meal and 0, 30 and 60% maize grain was estimated in three ways: (i) from the difference between the total non-ammonia N and microbial N entering the duodenum over a 24-hour period using 35S and DAPA as microbial markers, (H) from the disappearance of N from nylon bags in the rumen and the rate of outflow of rumen solids, and (iii) from the solubility of the feed N in a bicarbonate-phosphate buffer. The values obtained by methods (i) and (iii) decreased as the proportion of grain in the diet increased. Those given by method (H) showed no definite trend.
