Sites of digestion in the calf. I. The digestion of diets containing barley and wheat chaff supplemented with soya bean meal or urea

Abstract

Four Friesian bull calves were fitted with re-entrant duodenal cannulae within 1 week of birth. From 13 weeks of age the calves were fed on one of three diets all containing 17% crude protein. Diet A contained barley, 15% wheat chaff and soya bean meal, diet B barley, 15% wheat chaff and urea, and diet C barley, 45% wheat chaff and soya bean meal. The diets were given for 2 weeks, and on the last day of each feeding period total collections were made of the digesta leaving the abomasum over a 12 hr period. The diets were then changed so that each calf was offered each diet twice. The total apparent digestion of the organic matter in the diet containing 45% wheat straw was less than that of those containing 15% wheat straw. This was due to less digestion in both the stomach and hindgut. The flow of nitrogen from the abomasum, expressed as a percentage of the nitrogen intake, was less when the calves were fed on the diet containing urea (B) than when they were fed on those containing soya bean meal (A and C). Also, a larger proportion of the nitrogen was of microbial origin when they were on diet B. The proportion of essential amino acids in the total amino acids flowing from the abomasum was greater than that in the total amino acids present in all diets. Also, the apparent digestion of essential amino acids in the hindgut was greater than that of non-essential amino acids. It is calculated that methionine and threonine may be limiting for the growth of calves given diets A and B, while dietary metabolizable energy intake was probably the first factor limiting the growth of calves on diet C.