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In vitro effects of individual fatty acids on protozoal numbers and on fermentation products in ruminal fluid from cattle fed a high-concentrate, barley-based diet^1,2

A. N. Hristov^*, M. Ivan and T. A. McAllister^,3

^* Department of Animal and Veterinary Science, University of Idaho, Moscow 83844-2330 and and Agriculture and Agri-Food Canada Research Centre, Lethbridge, AB, Canada T1J 4B1

³ Correspondence: P.O. Box 3000 (phone: 403-317-2240; fax: 403-382-3156; e-mail: mcallister{at}agr.gc.ca).

The objective of this study was to investigate the effects of sodium salts of individual fatty acids on protozoal numbers and ruminal fermentation variables in vitro. Ruminal inoculum was obtained from two heifers fed a finishing diet consisting of (DM basis) 90% rolled barley grain, 4% barley silage, 5% soybean meal, and 1% mineralized salt. Fatty acids (FA) were included individually in the inoculum as follows: C6:0, C8:0, and C10:0 at concentrations (wt/vol) of 0.0625, 0.125, and 0.25%; C14:0 and C18:0 at concentrations of 0.125, 0.25, and 0.5%; and C12:0, C16:0, C18:1, C18:2, and C18:3 at concentrations of 0.25, 0.5, and 1.0%. ¹⁵N-Labeled casein was included as a N tracer. In the presence of medium-chain saturated FA (particularly C10:0 and C12:0), no ciliate protozoa (99.8% Entodinium spp.) were recovered from the incubation medium. Long-chain unsaturated FA (C18:3, C18:2, C18:1) also decreased (P < 0.05) protozoal numbers. At all concentrations tested, C10:0 and C12:0 decreased (P < 0.05) ammonia and total VFA concentrations (by 29 and 22%, respectively) and increased (P < 0.05) concentrations of total free amino acids, reducing sugars, and soluble protein. At the greatest concentrations of these FA, xylanase and amylase activities of the incubation media were decreased (P < 0.05). The C18 unsaturated FA increased (P < 0.05) the polysaccharide-degrading activities of the media. These in vitro results suggest that long-chain unsaturated FA in combination with medium-chain saturated acids have the potential to decrease protozoal numbers and ruminal ammonia utilization in cattle fed high-grain diets.

Key Words: Cattle • Fatty Acids • Ruminal Fermentation • Ruminal Protozoa

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