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Production and Metabolism of Volatile Fatty Acids, Glucose and CO₂ in Steers and the Effects of Monensin on Volatile Fatty Acid Kinetics¹

Nutritional Physiology Section, Department of Animal Science, Iowa State university, Ames, IA 50011

A study was conducted to determine effects of monensin supplementation on production and interconversion rates of rumen acetate, propionate, and butyrate and plasma acetate. Measurements were made by isotope dilution techniques in four Holstein steers fed a 70% alfalfa hay, 30% corn ration. In addition, a general kinetic method for solution of open systems has been applied to quantify metabolism of the rumen volatile fatty acids and glucose and the production of CO₂. Dietary monensin increased rumen propionate production at the expense of rumen acetate production so that total volatile fatty acid production was unchanged. Butyrate production tended to increase, indicating that decreased acetate production may result in diversion of hexose to propionate and butyrate production and direction of reducing equivalents away from methane production. These changes were calculated to increase rumen fermentation efficiency by 6%. Oxidation of the rumen volatile fatty acids and systemic plasma glucose accounted for only 35% of CO₂ production.

KEY WORDS: • monensin • volatile fatty acids • steers • in vivo kinetics • glucose

¹ Joumal Paper No. J-10781 of the Iowa Agricukure and Home Economics Experiment Station. Ames. Iowa. Project No. 2506. Supproted in part by funds provided by a grant from Eli Lilly and Co. Data are taken from a dissertation submitted to Iowa State University by L. E. A. to partly fulfill requirements for the Ph.D. degree. Preliminary papers were presented at the 72nd and 73rd Annual Meetings of the American Dairy Science Association, June 1981 and 1982. J. Dairy Sci. 64 (Suppl. 1), 131 (abs.) and J. Dairy Scl. 65, (Suppl. 1), 194 (abs.).

² Present address: Department of Dairy Science, University of Wisconsin. Madison, WI 53706.

³ Send reprint requests to: J. W. Young. Department of Animal Science. 313 Kildee Hall. Iowa State University. Ames. IA 50011.

Manuscript received 18 November 1982.

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