Photosensitization and hepatic disorders
Brachiaria brizantha, like other Brachiaria species, can cause a sporadic toxicity syndrome of hepatogenous photosensitivity. Sheep, goats and cattle develop skin lesions, facial oedema, liver damage (larger quantity of foamy macrophages in the hepatic parenchyma), mesenteric lymph nodes and ruminal stasis that result in severe drops in weight gain (down 40%) and possibly death if the animals are not removed from the pasture (Moreira et al., 2009). Poisoning has been reported with sheep grazing bread grass in Australia and Brazil (FAO, 2010; Lascano et al., 1996). The cause of toxicity appears to be the presence in the bile ducts and hepatocytes of crystals of salts of sapogenin glucuronides originating from steroidal saponins present in the plant. Sapogenins content varies according to environmental stress, plant age and developmental stage. Outbreaks of Brachiaria spp. poisoning in central western Brazil are frequently observed in pastures that had not been grazed for more than 30 days. They also occur during the growing stage of the pastures at the start of the rainy season (Brum et al., 2009).