Further investigation of the dietary protein level-monensin interrelationship in broiler chicks: influence of dietary protein source and type of anticoccidial drug.

Three experiments were conducted to evaluate the influence of dietary protein source on the monensin response in healthy chicks fed diets varying in CP. The interrelationship between dietary CP level and four different anticoccidial drugs was evaluated in a fourth experiment. The experiments were conducted from 8 to 21 or 22 days posthatching. In Experiment 1, crossbred chicks were fed corn-soybean meal (SBM) diets containing either 24 or 16% CP or casein-dextrose diets containing 20, 15, or 10% CP in the presence or absence of 160 mg/kg monensin. When CP level was decreased in the corn-SBM treatments, the resulting monensin-induced growth depression was greater. However, this interaction was not observed in chicks fed casein-dextrose diets. Experiments 2 and 3 were conducted to determine if the monensin-protein level interrelationship is influenced by the source of dietary soybean protein or by high levels of animal protein (AP). Monensin at 140 mg/kg produced a much greater growth depression at 16 than at 24% CP in chicks fed a corn-SBM diet, whereas amounts of monensin depression in chicks fed a corn-isolated soy protein diet were similar for both CP levels. As dietary protein was reduced from 24 to 16% in Experiment 3, 140 mg/kg monensin caused growth depressions of 10 and 40%, and 14 and 28%, respectively, in broiler chicks fed corn-SBM and corn-AP diets.(ABSTRACT TRUNCATED AT 250 WORDS)