Hepatogenous Photosensitization in Steer by Brachiaria decumbens

Background: Although the etiology of hepatogenous photosensitization has not yet been fully elucidated, it is known that hepatotoxic substances (saponins) present in grasses of the genus Brachiaria spp. are responsible for intoxication of ruminants and horses, causing great economic losses in the whole world. Since this grass is the source of food for the herd in Brazil, and other countries of the world, the aim of this paper is to describe the epidemiological, clinical, laboratory and anatomopathological aspects of a steer with this disease. Case: A 3-year-old Nellore steer was referred to veterinary care at a property in Bahia, with a 3-week history of swelling, loss of cutaneous tissue in the ear and scrotum region, and dry faeces. The animal was raised in pasture with Brachiaria decumbens along with five animals of different age and sex; however, it was the only one to present symptoms. Although the animal had been treated at the farm, there was no clinical improvement. On clinical examination, the steer was apathetic with jaundiced mucous membranes, nasal and ocular discharge, epiphora, and ulcers on the labial and gum commissure. The steer had leukocytosis with neutrophilia, anemia, and hyperfibrinogemia. The body condition score (BCS) was 2 (BCS ranges from 1 to 5), and the skin lesions observed were bedsores, necrosis and scabs in several regions. The increase in liver enzymes (GGT, AST) indicated hepatic impairment, suggesting a case of hepatogenous photosensitization. The therapeutic protocol instituted was enteral hydration, electrolyte replacement, topical application of ointment in the injured areas. In addition, it was recommended to maintain the animal in the shade, supply of good quality grass, and a new clinical evaluation in seven days. On new examination, it was observed that there was no satisfactory clinical improvement of the animal, and persistence of laboratory changes. Despite the poor prognosis, treatment was continued for another month with the same recommendations. However, in view of the severe clinical condition and unfavorable prognosis, the animal was submitted euthanasia. Necropsy revealed extensive areas of bedsores, erythema, severe jaundice in the mucous membranes, eyeballs and opaque corneas. The liver had an enlarged volume with bulging edges and a greenish color. The kidneys had a pale brownish color, with an irregular and mottled subcapsular surface, with blackened and depressed spots. Histologically, the cytoplasm of the hepatocytes was finely vacuolated, sometimes refringent and with an abundant presence of bile pigment. It was also observed in the middle of the liver parenchyma, multiple foci of accumulation of macrophages filled with vacuoles of different sizes containing saponins and crystals of saponins inside bile ducts. Furthermore, it was possible to observe hypertrophy and hyperplasia of Kupffer cells, disarrangement of hepatocytes with individual necrosis of hepatocytes. Discussion: The diagnosis of hepatogenous photosensitization was based on history, clinical, laboratory and anatomopathological findings. Serum biochemistry was important to measure hepatic impairment and possible secondary lesions, which were confirmed by the necropsy. Although hepatogenous photosensitization is less common in adult cattle, it must be considered in the differential diagnosis of skin lesions, reduced appetite, and jaundice. Since it was a sporadic case, individual predisposition is probably a preponderant factor.