Effects of intravenously infused zeranol on glucose kinetics in growing Holstein steers

Four Holstein steers fed 2.86 kg of corn and 3.50 kg of chopped alfalfa hay in 12 equal portions daily were used to determine effects of intravenously infused zeranol on glucose kinetics. In period I (1 wk), only carrier (9:1, propylene glycol:ethanol) was infused. Five [6-3H] glucose kinetic experiments were conducted on each of three steers, and three experiments were done on the fourth. In period II (2 wk), two steers were infused continuously with .9 mg zeranol daily via a vena cava catheter, and two were infused with 2.3 mg of zeranol. Six experiments were conducted per steer. In period III (2 wk), dosages were reversed for six more experiments. Period IV (2 wk) was a repeat of carrier infusion with three kinetic experiments per steer. Glucose kinetic averages for initial control, .9 mg zeranol, 2.3 mg zeranol, and final control were: irreversible loss (g/day), 1032, 1016, 992, and 1025; total entry rate (g/day), 2395, 2542, 2617, and 2438; recycling (g/day), 1362, 1558, 1625, and 1413; and pool size (g), 43.4, 45.4, 43.9, and 46.5. Combined control and treatment means were significantly different for total entry rate and recycling. Glucose irreversible loss is not affected by .9 or 2.3 mg of zeranol infused directly into the blood. Increases in total entry rate and recycling, however, suggest that zeranol may affect some aspects of glucose utilization and synthesis. Zeranol caused no changes in concentrations of blood glucose, growth hormone, insulin, or cortisol of plasma.