Dorsal thermal necrosis in a Brazilian sheep flock

ABSTRACT: Thermal burn injuries are very uncommon occurrences in small ruminants worldwide, and in Brazil, there are no descriptions of this condition. Herein we describe an outbreak of dorsal thermal necrosis in a flock of sheep in the municipality of Boca da Mata, in the Forest Zone of the State of Alagoas, Northeastern Brazil. Twelve ewes were separated from the flock for a general clinical examination and evaluation the serum levels of urea, creatinine, gamma-glutamyltransferase, and aspartate aminotransferase. In addition, biopsies of the skin and liver were performed on two severely affected sheep. The flock was raised in semi-intensively management in a pasture area without shading and receiving approximately eight hours of insolation daily and developed severe dermatitis that evolved to severe necrosis of the dorsal skin. Grossly, these lesions were only observed in the dorsal skin of black sheep, while sheep with white dorsal areas of skin were not affected. Microscopically, the epidermis and deep dermis of affected sheep showed diffuse coagulative necrosis, pigmentary incontinence, and parakeratotic hyperkeratosis. Dorsal thermal necrosis occurs only in the dorsal skin of black sheep in situations of excessive exposure to sunlight due to the accumulation of ultraviolet radiation. The distribution of the lesions, restricted to the dorsal area of the skin, is an important clinicopathological aspect in these cases that can help differentiate lesions caused by photosensitization, as they usually involve other anatomical sites. To the authors’ knowledge, this is the first report of dorsal thermal necrosis in sheep in Brazil.