The development of ruminant digestion in the calf. I. The digestion of barley and soya bean meal

Four male Friesian calves were fitted with re-entrant duodenal cannulae within 1 week of birth. To 5 weeks of age the calves were given milk, then weaned over 2 days and offered a diet containing 60% barley, 20% soya bean meal and 15% wheat chaff. Total collections of digesta flowing to the duodenum after weaning were made for 12-hr periods at weekly intervals for 8 weeks. Of the dry matter ingested, 76% was recovered at the duodenum 1 week after weaning, 58% at 2 weeks after weaning and 46% at 8 weeks after weaning. The digestion of acid detergent fibre (ADF) in the stomach was 20% in the first week after weaning and increased to 52% by 8 weeks. The flow of nitrogen to the duodenum was similar to the nitrogen intake. In the first week after weaning, 32% of the nitrogen flowing to the duodenum was of microbial origin; this increased to 74% by 7 weeks after weaning. The flow of essential amino acids to the duodenum as a percentage of intake was greater than that of non-essential amino acids. Also, the apparent digestion of essential amino acids in the intestines was greater than that of non-essential amino acids. By comparing the apparent digestion of amino acids in the hind gut with their requirement for the growth of the calves, it was calculated that methionine would be the first limiting amino acid and threonine the second.