Monensin toxicity in turkey breeder hens

High mortality in two flocks of 1900 turkey breeder hens accidentally fed 280 g monensin/ton of complete feed is described. Mortality attributed to the poisoning was 76% in flock 1 and 18% in flock 2. Clinically, turkeys were found dead, exhibited respiratory distress with wings extended laterally, had fine tremors, or showed posterior paresis and inability to rise. The most striking finding at necropsy was the almost complete absence of gross lesions. Some turkeys had severely congested lungs; however, many did not. A few birds had pale streaks within the adductor muscles of the legs. Microscopic lesions included myofiber degeneration and necrosis of skeletal and myocardial muscle. Serum phosphorus, lactate dehydrogenase, and creatine phosphokinase were markedly elevated, whereas potassium, chloride, and calcium values were lowered.