Further investigation of the dietary protein and monensin level interrelationship in broiler chicks: influence of Eimeria acervulina infection, increased dietary protein, and level of feed intake.

Three experiments were conducted to evaluate the influence of several dietary factors on the monensin response in commercial broiler chicks fed corn-soybean meal diets varying in crude protein (CP). All experiments were conducted between 8 and 22 days posthatching. Trial 1 had a 2 X 2 X 2 factorial design wherein diets containing 16 or 24% CP and 0 or 121 mg/kg monensin were fed in the presence and absence of Eimeria acervulina infection. The monensin-induced growth depression was greater at 16% CP than at 24% CP. Coccidial infection had no effect on the monensin X protein level interaction. Monensin supplementation markedly improved performance of chicks infected with E. acervulina. Trial 2 was conducted to determine if the monensin-induced depression in performance caused by feeding a high level of monensin (140 mg/kg) could be moderated by feeding a high protein diet. Monensin supplementation reduced growth rate 18 and 10% in chicks fed 20 and 24% CP, respectively. Increasing CP to 28% alleviated the adverse effects of monensin on weight gain. Pair-feeding was used in Trial 3 to determine the extent to which the monensin-induced growth depression observed in chicks fed low protein diets was due to reduced feed intake. As expected, reducing the dietary CP from 24 to 16% resulted in a marked increase in the growth depression caused by 121 mg/kg monensin. Pair-feeding indicated that most of monensin's adverse effects in low protein diets could be attributed to its anorexic properties.