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Influence of Ration Physical Form, Ruminal Degradable Nitrogen and Age on Rumen Epithelial Propionate and Acetate Transport and Some Enzymatic Activities¹

Department of Dairy Science, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061

Holstein bull calves were used to determine the influence of degradable nitrogen and ration physical form on rumen epithelial transport and enzymic activity. Rations contained 30, 45 and 60% ruminal degradable nitrogen (RDN), each with three forms (ground hay, GR; chopped hay, CH; and all concentrate, CONC). Rumen tissue samples were obtained by biopsy (8 weeks) and at slaughter (20 weeks). Acetate transport across rumen epithelium increased between 8 and 20 weeks in calves fed GR and CH, but not in calves fed CONC. Propionate transport was highest in calves fed GR and lowest in calves fed CONC at both 8 and 20 weeks. Transport of acetate and propionate was increased with increasing RDN at 20 weeks. There were no differences in ruminal tissue lactate production. Rumen papillae of calves fed CONC were abnormal in morphology and at 20 weeks dry mucosal weights (mg/cm²) were highest. Lactate dehydrogenase and NADP-malic dehydrogenase activities were not different. Propionyl CoA synthetase activity was higher in 20-week calves fed CONC, compared to GR or CH. Glutamate dehydrogenase and aspartate aminotransferase activities were highest in 20-week calves fed 60% RDN rations, regardless of physical form.

KEY WORDS: • ration • transport rate • rumen degradable nitrogen • calves

¹ Partially supported by the John Lee Pratt Animal Nutrition Program.

Manuscript received 10 March 1980.

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