The Journal of Nutrition Vol. 127 No. 1 January 1997, pp. 171-176
Copyright ©1997 by the American Society for Nutritional Sciences

Sodium Mercaptoacetate Is Not a Useful Probe to Study the Role of Fat in Regulation of Feed Intake in Dairy Cattle

Manuscript received 15 April 1996. Initial reviews completed 18 June 1996. Revision accepted 16 September 1996.

Byung-Ryul Choi^*, Donald L. Palmquist^*, , and Michael S. Allen

^* Department of Animal Sciences, Ohio Agricultural Research and Development Center, The Ohio State University, Wooster, OH 44691-4096 and  Department of Animal Science, Michigan State University, East Lansing, MI 48824

Inhibition of fatty acid oxidation by mercaptoacetate stimulates food intake of rats fed dietary fat. To study regulation of feed intake of ruminants fed fat, dry matter intake and plasma concentrations of insulin and metabolites were determined in eight nonpregnant Holstein heifers in a cross-over design with two 14-d feeding periods by using a 2 × 2 factorial arrangement of treatments. Treatments were combinations of diet (27 or 103 g fatty acids/kg food dry matter) and injection (mercaptoacetate or saline). Half the heifers were fed each diet in Period 1, and diets were reversed in Period 2. On d 10 of each period, two animals per treatment were injected intravenously with either mercaptoacetate (300 µmol/kg body weight^0.75) or saline at 2 h postfeeding. Injections were reversed on d 12. Dry matter intake was suppressed by the high fat diet. Intravenous injection of mercaptoacetate decreased dry matter intake to 25% that of the control during 4 h postinjection. Both the high fat diet and mercaptoacetate injection increased plasma non-esterified fatty acid concentration, whereas plasma -hydroxybutyrate concentration was lowered by the high fat diet and by mercaptoacetate injection. Plasma triglyceride concentration was increased by the high fat diet, but was decreased by mercaptoacetate injection. Mercaptoacetate elevated plasma glucose concentrations at 2 and 3 h postinjection, possibly because plasma insulin concentration was lower. Effects of mercaptoacetate on plasma insulin and metabolite concentrations may have been confounded by the effects of decreased feed intake. Therefore, direct effects of mercaptoacetate injection were not separated from effects of feed intake on plasma insulin and metabolite concentrations. Because mercaptoacetate injection decreased dry matter intake it was not a useful probe to study mechanisms of feed intake regulation in dairy cattle fed fat.

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