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Measurement of Ruminal Volatile Fatty Acid Production from Alfalfa Hay or Corn Silage Rations Using a Continuous Infusion Isotope Dilution Technique^{1, 2,}

Department of Dairy Science, University of Wisconsin, Madison

ABSTRACT

A continuous infusion isotope dilution technique was used to measure ruminal volatile fatty acid (VFA) production in a nonlactating cow. Equal portions of the daily ration of alfalfa hay (H) or corn silage (S) were fed every hour. Daily dry matter (DM) intake was 3.9 kg of silage or 3.5 kg of the hay. Following a priming dose of acetate-1-¹⁴C, butyrate-1-¹⁴C, or propionate-2-¹⁴C, the same acid was continuously infused into the rumen for 10, 10, and 8 hours, respectively. Steady-state conditions were obtained during the final two hours of each infusion. Interconversion of carbon between acetate and butyrate was extensive. With the silage ration, 72% of the butyrate carbon was in equilibrium with 15% of the acetate carbon. With the hay ration, 62% of the butyrate carbon was in equilibrium with 18% of the acetate carbon. Little propionate was randomized.

A three-compartment model was used to correct for the interconversion of the volatile fatty acid carbon in the rumen, enabling determination of net volatile fatty acid production. The daily ruminal production of acetate, propionate, and butyrate for the silage and hay rations were, respectively, 19.6, 6.7, and 4.6 and 19.6, 5.2, and 1.9 moles. Total ruminal volatile acid production (moles) per kilogram of dry matter intake was 8.8 with silage, and 6.8 with the hay. The proportions of the individual volatile acids were similar, whether determined from the ruminal concentration or the daily volatile fatty acid production.

¹ Published with the approval of the Director of the Wisconsin Agrioultural Experiment Station.

² This study was supported by funds from the Graduate School Research Committee, University of Wisconsin.

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