Pathological studies on systemic mycoses in calves.

Systemic mycoses were found in 19 (4.7%) of 406 calves less than 6 months old which were autopsied during the past 10 years. Alimentary mycosis occurred in 12 (63.2%) of 19 cases. In alimentary mycosis, mucormycosis showed the highest rate of occurrence (91.7%, 11/12 calves) followed by aspergillosis 41.7% and candidiasis was 9.3%. Mucormycosis and aspergillosis were characterized by focal hemorrhagic necroses with hyphal proliferation and thrombi in the mucosa and muscular layers of the forestomach, abomasum, and small intestine. Candidiasis was characterized by hyperkeratosis with pseudohyphae and microconidia in the mucosa of the omasum. Four of 12 calves (33.3%) had mixed infections of the alimentary tract consisting of Mucorales and Aspergillus species. Pulmonary aspergillosis was found in 10 (52.6%) of 19 calves. There were micro-abscesses with hyphal proliferation or asteroid bodies in the lungs. Infections involving both the alimentary tract and respiratory organs were noted in 3 (10.5%) of 19 calves. Disseminated mycosis was found only in one calf. In alimentary mycosis, administration of antibiotics for the treatment of diarrhea and early weaning were thought to be an important predisposing factor.