Effect of Age and Diet on in Vitro Metabolism in Rumen Epithelium From Holstein Calves

Fresh rumen epithelial tissue was collected from calves slaughtered at 3, 12, 19, 30 and 60 d of age. These calves were fed milk until 28 d of age and had received starter and hay after 10 d of age. Samples also were collected at 30 and 60 d of age from calves fed only milk. Epithelial tissue was incubated with combinations of volatile fatty acids and sources of ammonia to measure some of the metabolic end products as indicators of metabolism and physiological development. Ketone bodies were the major product of volatile fatty acid metabolism by epithelial tissue under these incubation conditions. By 60 d of age, the weaned calves were producing ketones at rates similar to those reported previously for mature tissue and at approximately 40% of the mature rate at 30 d of age. At 60 d of age, milk-fed calves were producing ketones at 10–15% of mature levels. Very young and milk-fed calves appeared to produce more lactic acid than did older calves that were weaned onto dry feeds. There was no net glucose production, however, there was some accumulation of glucose in the incubations of epithelium from calves at 19 d of age. This may be related to a shift in epithelial metabolism occurring at this age.