Functional Development of Rumen Mucosa. II. Metabolic Activity

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Abstract
The objective was to determine the effect of diet on metabolic activity of rumen mucosa. Three Holstein calves were fed milk (M) and 3 received milk, hay, and grain (MHG). The calves were sacrificed at 16 wk of age. Mucosa from the anterior dorsal sac was stripped from the mucsle and placed temporarily in icecold Ringer. Two-gram samples were incubated at 39[degree]C for 3 hr in Krebs-Ringer-bicarbonate buffered at pH 7.2 in a 95:5 atomsphere of oxygen and carbon dioxide. Two hundred micromoles of acetate, propionate, butyrate, an equimolar mixture of these 3, or glucose, were added to the medium. Mean uptake of these substrates was (micromoles per 100mg dry tissue per 3 hr) 5.9, 29.6, 44.1, 31.5, and 3.8, respectively, for MHG 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 ketones was 72 and 88, respectively, for MHG calves and 17 and 29, respectively, for M calves.