Functional Development of Rumen Mucosa. II. Metabolic Activity

Abstract

The objective of the present study was to determine the effect of diet on metabolic activity of rumen mucosa. Three Holstein calves were fed milk (M) and three received milk, hay, and grain (MHG). The calves were sacrificed at 16 wk of age. Mueosa from the anterior dorsal sac was stripped from the muscle and placed temporarily in ice-cold Ringer. Two-gram samples were incubated at 39 C for 3 hr in Krebs-Ringer-bicarbonate buffered at pit 7.2 in a 95:5 atmosphere of oxygen and carbon dioxide. Two hundred micromoles of acetate, propionate, butyrate, an equimolar mixture of these three, or glucose, were added to the medium. Mean uptake of these substrates was (micromoles per 100 mg dry tissue per 3 hr) 5.9, 29.6, 44.1, 31.5, and 3.8, respectively, for MUG calves and 2.9, 5.8, 4.7, 5.8, and 4.2, respectively, for M calves. Ketones were produced from acetate, butyrate, and the equimolar mix. Percentage conversion of acetate and butyrate to ke~ones was 72 and 88, respectively, for MHG calves and 17 and 29, respectively, for M calves. The relationship of the metabolic activity to the structural development and absorptive ability of the rumen mucosa is discussed. The introduction of solid feed into the diet at four days or at 18 wk led to a marked increase in absorptive ability. The changes in absorptive ability were closely related to the degree of papillary development, but it was apparent that physiological changes in the rumen mueosa were also involved. The nature of these physiological changes was suggested by Sander et al. (17) and Armstrong et aI. (1), who proposed that an actively metabolizing rumen mucosa would stimulate the structural development and the absorptive ability of the mueosa.