Influence of anticoccidial drugs on losses of broiler chickens from heat stress and coccidiosis.

A floor-pen experiment conducted to study the anticoccidial efficacy of a number of drugs coincided with prolonged periods of hot weather and provided a good opportunity to study the interactions of anticoccidial drugs and environmental temperature. Six replicates of 60 day-old male chicks were fed one of the experimental diets for 48 days followed by a 5-day withdrawal period. The treatments consisted of unmedicated, salinomycin (60 ppm), monensin (100 ppm), arprinocid (60 ppm), halofuginone (3 ppm), amprolium/ethopabate (125/4 ppm), nicarbazin (125 ppm), and clopidol (125 ppm). Coccidiosis exposure was produced by mixing the suspensions of oocysts with the feed. Eleven heat related mortality episodes were recorded in the period of the experiment. All the mortality peaks were recorded at environmental temperatures at or above 37.8 C and relative humidity of 80 to 98%. Heat stress caused an excessive mortality in nicarbazin treated birds at an early age (18 to 29 days of age), while heat related mortality was low at this age with other drug treatments. Total heat related mortality with nicarbazin treated birds was significantly higher (59.2%) than the other treatments (8 to 18.6%). In order to investigate further the interaction of environmental temperature and nicarbazin, two battery trials were conducted in controlled environmental rooms. No heat stress mortality was recorded in the period of the first trial when nicarbazin treated birds were exposed to a constant environmental temperature of 32.2 C; however, their performance was affected. The results of the second trail showed that when nicarbazin treated birds were exposed to a constant environmental temperature of 37.8 C they suffered more severely from the heat stress than the unmedicated group in a short period of time. The results of these experiments confirmed that an interaction exists between high environmental temperatures and the anticoccidial drug nicarbazin.