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Evaluation of solar exposure on the experimental intoxication by Brachiaria decumbens in sheep

Stephen T. Lee
Pesquisa Veterinaria Brasileira 2013 v.33 no.8 pp. 1009-1015
aspartate transaminase, conjunctivitis, Cynodon dactylon, necrosis, Brachiaria, Cenchrus purpureus, lambs, necropsy, blood sampling, pastures, macrophages, photosensitivity, jaundice, ad libitum feeding, poisoning, grasses, solar radiation, blood serum, emotions, flocks, grass hay, gamma-glutamyltransferase, biopsy, toxicity, bile ducts, Urochloa decumbens, weight loss, histopathology, hyperplasia, hepatocytes, liver, dermatitis
Twenty-six five-month-old lambs originated from flocks with no previous contact with Brachiaria spp. pastures were divided into three groups. Two groups (GS and GSB) were fed daily with fresh harvested Brachiaria decumbens ad libitum. GS was kept in an area with solar exposure and GSB was kept in stalls sheltered from solar exposure. Control group (GC) was also kept under solar exposure, but fed with Cynodon dactylon grass hay and Pennisetum purpureum fresh grass. All sheep from the three groups were supplemented with 200g daily of a commercial concentrated food. Evaluation of clinical signs was carried out daily and blood samples were collected twice a week to determine AST and GGT serum activities. Three out of nine lambs of GS presented clinical signs of Brachiaria spp. poisoning, and two died. One animal showed clinical signs and died in GSB. The main clinical signs observed were apathy, weight loss, photophobia, conjunctivitis, ocular mucous discharge and jaundice. Dermatitis due to photosensitization was not observed. Mean serum AST and GGT activities were significantly higher (p<0,05) in the group exposed to sun, than in the other two groups, and the GGT activities were significantly higher in the group sheltered than in the control group (p<0,05). All animals at the end of the experiment were submitted to liver biopsy and died lambs were necropsied. Histopathological evaluation of liver samples from sheep with clinical signs evidenced swelling and vacuolization of hepatocytes, individual hepatocytes necrosis, presence of foamy macrophages, crystal negative images within bile ducts and foamy macrophages, biliary duct hyperplasia and periportal mononuclear infiltration. These results suggest that sun exposure does not define intoxication, but exacerbates the toxicity of the grass.