Brachiaria species are important forages from tropical regions such as Africa, Asia, Australia and South America. In the Brazilian Cerrado (savanna) there are around 51 millions hectares of Brachiaria spp, mainly Brachiaria brizantha (30 millions ha), Brachiaria decumbens (15 millions ha), Brachiaria humidicola and others (6 millions ha) (Macedo 2005).
In Brazil, spontaneous cases of hepatogenous photosensiti-zation by B. decumbens had been reported in cattle (Meagher et al. 1996, Lemos et al. 1997), sheep (Lemos et al. 1996a), and goats (Lemos et al. 1998). Poisoning by Brachiaria brizantha is reported in cattle (Lemos et al. 1996b) and in sheep (A.A. Lemos, personal communication). Initially, the disease was attributed to sporidesmin produces by Phitomyces chartarum spores in the pastures (Nobre & Andrade 1976, Fioravanti 1999), however histologic alterations of cholangiohepatopathy associated to crystals similar to those found in poisoning by Panicum spp. (Bridges et al. 1987), Narthecium ossifragum (Ceh & Hauge 1981), Agave lecheguilla (Camp et al. 1988) and Tribulus terrestris (Glastonbury et al. 1984) suggested that Brachiaria spp poisoning was due to lithogenic saponins contained in the plant (Lemos et al. 1996a, Lemos et al. 1997, 1998). Two steroidal sapogenins, yamogenin and diosgenin, were identified as the toxic principles of B. decumbens (Smith & Miles 1993, Cruz et al. 2000), and the disease was reproduced in sheep through administration of fractionated extracts of B. decumbens (Cruz et al. 2001).
The aim of this study was to describe an outbreak of hepatogenous photosensitization in sheep grazing B. decumbens and to establish whether, in this case, the photosensitization was caused by higher levels of protodioscin, a steroidal saponin isolated from B. decumbens (Haraguchi et al. 2003), or by spores of P. chartarum present in the grass.
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