Vicism or vetch toxicosis
Vicia benghalensis seeds and forage have been reported to cause poisoning in humans and livestock (vicism, vetch toxicosis, vetch-associated disease) (Kobert, 1906; Enneking, 1995a). Lethal vetch toxicosis was reported in 1931 in 5-6 month-old pigs fed a mixture of Vicia sativa and Vicia benghalensis seeds included at 12.5% of the diet (Clough, 1931 cited by Enneking, 1995a). Cases of poisoning have been reported with cows and horse grazing purple vetch in South Africa. The latter suffered from emaciation conjunctivitis, blepharitis and severe alopecia. Histopathological lesions were compatible with systemic granulomatous equine disease (Green et al., 1989; Woods et al., 1992). The cause of vetch toxicosis in purple vetch has been debated: canavanine (a non-protein amino acid) may play a role in this toxicity (Enneking, 1995b).
L-canavanine
Seeds of purple vetch contain high levels (1.9-3.4 g/kg) of the toxic non-protein amino acid L-canavanine (Enneking, 1995b). After flowering, the levels of L-canavanine increase with seeds formation and make the use of purple vetch unsafe in the absence of alternative fodder sources (Tate et al., 2006).