Seed toxins
Like other Vicia species, the seeds of Vicia sativa contain numerous antinutritional factors, notably cyanogenic amino acids and cyanogenic glycosides that are toxic to monogastric animals. Vicia sativa has been implicated in numerous cases of poisoning leading to stock losses. Its use in pigs, poultry (the latter being the most sensitive) and humans is therefore restricted (Tate et al., 2006). 60% unprocessed Vicia sativa seeds in the diet were detrimental to broilers and laying hens: they caused 100% mortality in broilers, with a survival time of 5.1 days, and a cessation of egg production in layers within 14 days (Farran et al., 2001a). Among other birds, only pigeons seem to have no problem with Vicia sativa seeds (Enneking, 1995).
The amount of toxicants is inversely correlated to the seed size. The most important toxin is the γ-glutamyl-β-cyanoalanine, which affects the conversion of methionine to cysteine, and has indirect effects on glutathione metabolism (Collins et al., 2002). The toxins are damaging to the nervous system with signs such as convulsion and leg paralysis. Feeding horses with Vicia sativa seeds causes brain disease with symptoms of acute brain oedema (Enneking, 1995). Some varieties have low cyanoalanine levels but still contain cyanoglycosides. Selection of low cyanogenic varieties by breeding would make it easier to include Vicia sativa seeds in pig and poultry diets (Tate et al., 2006). Post-harvest detoxification treatments such as mild acid hydrolysis proved to be effective but remain costly (Enneking, 1995).
In 1992/1993, and later in 1998/1999, Australian exports of potentially toxic Vicia sativa seeds to India, Egypt, Saudi Arabia, Sri-Lanka, Pakistan and Bangladesh as a cheap replacement for red lentils (Lens culinaris Med.) caused a minor international crisis and a ban on importations of Australian vetch (Enneking, 1995; Tate et al., 1999).
Forage
Vicia sativa forage does not normally contain antinutritional factors when it is grazed or cut frequently enough to prevent flowering and seed-heading. However, some cases of poisoning of ruminants consuming common vetch forage have been reported: signs include severe dermatitis, skin edema, conjunctivitis, corneal ulcers, and diarrhea. About 50% of affected animals die (Mayland et al., 2007). In one instance, 5 cows died after being fed 5 kg/day of Vicia sativa hay (Suter, 2002).