Two trials were conducted to evaluate the influence of forage level on the response of feedlot cattle to
salinomycin. Diets containing 10, 15 and 20% forage were compared with 0 or 11 mg/kg
salinomycin. In trial 1, treatment effects on feedlot performance were evaluated using 108 crossbred steers (295 kg) in a crossover design experiment. There were no
salinomycin X forage level interactions (P greater than .20).
Weight gain response to
salinomycin supplementation averaged 5.4, 5.3 and 6.9%, respectively, for diets containing 10, 15 and 20% forage. Corresponding values for feed conversion response to
salinomycin supplementation were 5.1, 3.9 and 5.9%. Averaged across forage level,
salinomycin supplementation improved rate of
weight gain and feed conversion by 5.9 and 5.2%, respectively (P less than .01). In trial 2, treatment effects on characteristics of ruminal and total tract digestion were evaluated in a 6 X 6 Latin-square design trial involving six crossbred steers (191 kg) with
cannulae in the rumen and proximal duodenum. There were no interactions between
salinomycin supplementation and forage level on characteristics of ruminal digestion (P greater than .20).
Salinomycin supplementation did not influence synthesis of microbial N, ruminal digestion of organic matter,
acid detergent fiber and
starch, or molar proportions of
acetate,
propionate and
butyrate (P greater than .20).
Salinomycin supplementation increased passage of non-
ammonia N to the small intestine (5.4%, P less than .10) and increased ruminal escape of feed N (24%, P less than .01).(ABSTRACT TRUNCATED AT 250 WORDS)