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.