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Ionophores Alter Hepatic Concentrations of Intermediary Carbohydrate Metabolites in Steers^1,2,

Texas A&M University and Texas Agricultural Experiment Station, College Station 77843

Abstract

The effects of ionophores on liver weight and function were determined in finishing steers (n = 24; avg weight 440 kg). Steers were group-fed one of three treatments (control, lasalocid or monensin at 33 mg/kg feed) for 46 d prior to slaughter. Three days prior to slaughter, blood was collected for the determination of serum Ca and Mg. At slaughter, the liver was removed, weighed, sampled, frozen in liquid nitrogen and subsequently analyzed for concentrations of carbohydrate metabolites and minerals. Liver weight (5.9 kg) was unaffected by treatment. Serum and hepatic Ca and Mg were not affected by ionophore treatment. Hepatic glycogen levels in steers fed ionophores were unaffected by treatment Fructose 1,6-bisphosphate was 21% lower (P < .10) in hepatic tissue of steers fed ionophores, whereas dihydroxyacetone phosphate was 15 to 37% greater in hepatic tissue of steers fed monensin (P < .20) or lasalocid (P < .10). Glyceraldehyde 3-phosphate was elevated more extensively by lasalocid than by monensin with increases of 72 (P < .05) and 132% (P < .001), respectively, over controls. Glycerol 3-phosphate levels were 37% (P < .05) and 12% (NS) greater with these ionophores. Hepatic levels of pyruvate were elevated 12 (NS) to 36% (P < .17) for monensin and lasalocid. Fructose 2,6-bisphosphate levels were 25% lower (P < .25) in hepatic tissue of steers fed ionophores than in hepatic tissue from control steers. Other metabolites of carbohydrate metabolism in hepatic tissue were not altered appreciably. Changes in levels of intermediary metabolites of carbohydrate metabolism suggest alterations in hepatic carbohydrate metabolism favoring gluconeogenesis in steers fed ionophores.

¹ Journal paper TA 23447, Beef Cattle Nutrition and Growth Section, Dept. of Anim. Sci., Texas A&M Univ. and Texas Agric. Exp. Sta.

² Reference to a company or trade name does not imply approval or endorsement by the Texas Agric. Exp. Sta.

³ Current address: Center for Vet. Med., Food and Drug Admin., Rockville, MD 20857.

⁴ Dept. of Anim. Sci.

⁵ McGregor Res. Center, McGregor, TX.