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Volatile Fatty Acid Metabolism by Rumen Mucosa from Cattle Fed Hay or Grain¹

Department of Animal Science, Iowa State University, Ames, 50010

ABSTRACT

Effects of an all-grain versus an all-hay diet on metabolic activity of rumen mucosa of cattle were investigated. After diets had been fed for 3 to 4 mo, rumen papillae were collected at slaughter from the dorsal rumen sac and incubated with one of various volatile fatty acids. Rates of substrate utilization were in the order: n-butyrate >> n-valerate ~ propionate > iso-butyrate ~ iso-valerate. Overall, papillae from hay-fed steers utilized greater amounts of volatile fatty acids. Dietary treatment did not significantly affect extent of conversion of volatile fatty acids to lactate and to ketone bodies. Lactate was the major metabolite from propionate and n-valerate. Ketone body formation accounted for more than 90% of n-butyrate uptake by papillae. Ketone formation from n-valerate was restricted to ß-hydroxybutyrate while that from iso-valerate was essentially acetoacetate plus acetone. Metabolic systems in rumen mucosa of physiologically mature ruminants seem to adapt little to varying individual volatile fatty acids available for absorption in vivo.

¹ Journal paper J-8035 of the Iowa Agriculture and Home Economics Experiment Station, Ames. Project 1908. Supported in part by funds from grants HE-04969 and AM-10706 from the U.S. Department of Health, Education, and Welfare.

² Present address: Institute of Animal Nutrition, Technical University of Munich, D 8050 Freising-Weihenstephan, Federal Republic of Germany. Requests for reprints should be J. W. Young.

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