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Effect of 1-Methyl-2-Mercaptoimidazole (Tapazole^R)¹ Feeding on Muscle Characteristics, Fiber Type and Fatty Acid Composition of Charolais-Hereford Steers^,2

University of Kentucky,³ Lexington 40506

Abstract

Steers fed 800 mg tapazole per day had a significantly greater ADG and weighed more after a 112-day feeding experiment than control steers. However, the control cattle had slightly less subcutaneous fat and more marbling than the treated steers, resulting in a higher quality grade for the control steers. The rib eye area was significantly larger, the conformation grade higher, and muscle color lighter in the treated steers than in control animals.

Muscles from the control steers contained slightly more aerobic (type I) type muscle fibers as measured by DPNH-TR and Sudan Black B stains. However, the type I fibers were larger in the treated animals and the type II fibers larger in the control animals. As a result, the area occupied by type I and type II fibers was essentially the same between the two groups of animals.

The adipose tissue of the control steers contained significantly more C18:1, C18:2, sat. 8 (an unidentified saturated fatty acid eluted just before C18:0) and total unsaturated fatty acids than did tapazole-treated cattle. Muscle lipids contained significantly less C14:0, sat. 2 and sat. 3 and more sat. 4 (unidentified saturated fatty acids eluted between C14:0 and C16:0) and C18:2 fatty acids than the depot fats. The external fats contained significantly more sat. 2 and C16:1 and less sat. 7 (unidentified saturated fatty acid eluted just after C16:1) fatty acids than internal fats. There was no significant differences in tenderness between tapazole fed and control steers.

¹ Eli Lilly and Company, Indianapolis, Indiana

² The investigation reported in this paper (72-5-146) is in connection with a project of the Kentucky Agricultural Experiment Station and is published with approval of the Director.

³ Department of Animal Sciences.