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Intravenous Administration of Ionophores in Ruminants: Effects on Metabolism Independent of the Rumen¹

North Carolina State University, Raleigh 27695-7621

Abstract

The effect of i.v. administration of ionophores on metabolism in ruminants was investigated in two experiments. In Exp. 1, four Angus heifers were assigned randomly to receive i.v. monensin (18 mg, n = 2) or vehicle (control, n = 2). Samples were collected from indwelling vena cava cannulas from –60 to 240 min. Concentrations of K, Mg (P < .05) and P (P < .10) were lower and glucose (GLU) and free fatty acids (FFA) were higher (P < .05) in monensin-treated than in control heifers. Serum insulin (INS) initially declined and subsequently increased (P < .05) following monensin administration. A second experiment was conducted to determine the effect of a higher dose of monensin and the effect of lasalocid on minerals and metabolites. Angus (n = 3) and Hereford (n = 3) steers were randomly assigned to treatments in two 3 x 3 latin square designs. Treatments were i.v. administration of monensin, lasalocid or vehicle (ethanol) administered on three consecutive days. Administration of monensin, but not vehicle or lasalocid, resulted in ataxia, hypernea, polyuria and anorexia for approximately 2 h. Plasma concentrations of K, P and Mg were suppressed (P < .05) by monensin, but not by vehicle or lasalocid administration. The decrease in K was preceded by a transient increase in K 15 min after administering monensin. Concentrations of GLU and FFA increased (P < .05) following monensin administration. Concentrations of INS were lower from 60 to 120 min and greater at 180 and 240 min compared with –60 to 0 min from monensin administration (P < .05). These results provide first evidence of an effect of monensin on metabolism in ruminants independent of alterations in ruminal microbial metabolism.

¹ Paper No. 11375 of the Journal Series of the North Carolina Agric. Res. Serv., Raleigh 27695-7601. The use of trade names in this publication does not imply endorsement by the North Carolina Agric. Res. Serv. of the products named, nor criticism of similar ones not mentioned. Purified bovine LH (LER 1716-2) was kindly supplied by L. E. Reichert, Jr., Albany Medical College, Albany, NY; bovine LH antiserum by T. E. Riser, Univ. of Georgia, Athens; purified ovine GH antiserum and ovine GH by A. F. Parlow, Pituitary Hormones and Antisera Center, Torrance, CA. Appreciation is expressed to L. Samsell, B. Hogarth, K. Ferris, S. West and C. Marsh, Jr. for excellent assistance in animal care, data analyses and in performing assays.

² Dept. of Anim. Sci.