EFFECTS OF LASALOCID AND MONENSIN PLUS TYLOSIN ON SERUM METABOLIC HORMONES AND CLINICAL-CHEMISTRY PROFILES OF BEEF STEERS FED A 90-PERCENT CONCENTRATE DIET

Fourteen crossbred beef steers (average initial BW 313 +/- 13.1 kg) fe d a 90% concentrate diet (as-fed basis) were used to evaluate effects of ionophores on serum metabolic hormones and clinical chemistry profi les. Treatments were no ionophore (C; four steers), lasalocid (L; 33 m g/kg of diet; five steers), and monensin (33 mg/kg of diet) plus tylos in (11 mg/kg of diet; MT; five steers). All steers were adapted to the 90% concentrate diet, after which treatments were applied and blood w as sampled via jugular catheters on d 7, 35, 63, 91, and 119 of the tr ial at 0, 1, 2, 3, 4, 6, 8, and 10 h after feeding. Averaged over samp ling days, serum glucose concentrations did not differ (P > .10) among treatments at any sampling time (treatment x sampling time, P < .05). Averaged across sampling days and times, serum growth hormone, insuli n, cholesterol, and triglyceride concentrations did not differ (P > .1 0) among treatments. No major effects of ionophores were noted for ser um enzymes or protein fractions. Averaged over sampling times within d ay (treatment x day interaction, P < .10), both L and MT increased (P < .05) serum Ca and Na concentrations on d 91 and 119 compared with C. Serum inorganic P was increased (P < .10) for L vs MT and for ionopho re treatments compared with C (P < .10) on several occasions (treatmen t x day x sampling time interaction, P < .05). Results suggest that io nophores do not cause dramatic changes in serum metabolic hormones or clinical chemistry profiles; however, monensin and lasalocid altered s erum minerals in beef steers fed a high-concentrate diet.