Abstract
The effect of dietary salinomycin supplementation (200mg/head/day) on insulin secretory response to feeding was investigated using 16 Japanese shorthorn steers (initial age, approxi. 314 days; average initial weight, 329kg). Four steers were allotted to each of four treatments providing either a low (0.6% concentrate of body weight) or a high (1.8% concentrate of body weight) concentrate diet supplemented with or without salinomycin in a 2×2 factorial arrangement of treatments. All groups were provided alfalfa hay ad libitum throughout the fattening period of 10 months. Dietary salinomycin did not influence the rates of gain in fattening steers. There was no significant salinomycin×concentrate level interaction on feed conversion. Steers fed the salinomycin diet converted (P<0.10) the feed to gain 14% more efficiently than the unsupplemented diet-fed steers due to the lower rates of feed intake. Dietary salinomycin increased ruminal molar percentages of propionate after feeding and decreased ruminal butyrate proportions, but did not influence ruminal acetate proportions. There was no significant difference in plasma glucose concentrations at any time after feeding between dietary salinomycin treatments. Plasma insulin concentrations in steers fed the salinomycin diet were higher than those of the unsupplemented diet-fed steers at 4-6 hrs after feeding in the high concentrate diet. Dietary salinomycin also increased (P<0.05) the plasma insulin area over 360 min after feeding across the concentrate level. These results indicated that dietary salinomycin stimulated insulin secretory response to feeding in fattening steers. This may partly account for improved feed conversion of steers fed the salinomycin diet.
