Effects of 4-methylimidazole in young calves

Clinical signs, gross and histologic necropsy findings and dose response curves of 4-methylimidazole (4-MI) were determined in young Holstein calves. Three-day-old Holstein bull calves were given an oral dose of 0,25,50,100,200 or 400 mg 4-MI/kg body weight. Acute clinical signs were hypersalivation, mouth chomping, diarrhea, muscle fasciculations, tremors, hyperexcitability, convulsions, coma and death. Death occurred within 3 hr for calves given the highest dose of 400 mg/kg. Two of 3 calves dosed at 200 mg/kg died within 8 and 3/4 hr of dosing. Only 1 of 3 calves showed mild signs at the 100 mg/kg dose level and no effects were observed at the 50 or 25 mg/kg dose level. Signs due to 4-MI in this experiment were similar to signs observed in calves whose dams were consuming ammoniated hay. No pathological lesions attributable to 4-MI toxicosis were found during gross or microscopic necropsy examination. Blood chemistry values from calves treated with 4-MI were within normal ranges except for potassium, phosphorus and glucose which were elevated (P less than .05) at the time of death for those calves dosed at 400 mg/kg.