Monensin efficacy in rations containing suboptimal energy or protein.

Experiments were performed with growing chicks to assess the effects of rations deficient in energy and protein on feed intake, quantity of monensin ingested, and overall anticoccidial efficacy. Experiment 1 employed a 4 X 2 X 2 factorial design where four levels of monensin (0, 70, 90, and 110 ppm) were added to rations containing either 17 or 23.5% crude protein. In Experiment 2, identical levels of monensin were added to diets containing either 2600 or 3200 kcal metabolizable energy/kg. Both studies were conducted in the presence and the absence of infections produced by Eimeria acervulina, E. maxima, and E tenella. Chicks fed diets deficient in protein consumed significantly more feed and gained less weight than those fed rations adequate in protein. Likewise, protein-deficient chicks consumed more monensin per kilogram of body weight gain. In Experiment 2, weight gain and feed intake were greater in birds fed adequate energy, but the quantity of monensin consumed per kilogram of weight gain was greatest in energy-deficient chicks. In both experiments coccidial lesions and oocyst output were controlled more effectively as monensin dosage was increased. Neither protein nor energy interacted significantly with monensin when lesion scores and oocyst output were evaluated. Thus, these studies indicate that coccidiosis control offered by the monensin concentrations studies is independent of the protein or energy content of the ration.