Poisoning
The seeds and vegetative parts of hairy vetch can be poisonous to livestock, including cattle, horses and poultry, but the etiology of the toxicity remains elusive (Cooper et al., 1984; Anderson et al., 1983; Kerr et al., 1982). In cattle, the consumption of hairy vetch has been linked to a systemic granulomatous disease. Three different syndromes have been reported. The first syndrome, associated with the ingestion of hairy vetch seeds, resulted in acute nervous derangement, pain, convulsions and death (Claughton et al., 1954). A second syndrome, associated with consumption of hairy vetch pasture, resulted in death of cattle with signs that included subcutaneous swellings of the head, neck and body, eruptions in the oral mucous membranes, purulent nasal discharge, cough, and congestion. The third syndrome, also associated with consumption of vetch pasture, is characterized by dermatitis, conjunctivitis and diarrhea, together with lesions that include extensive infiltration of organs by monocytes, lymphoplasmacytic cells, multinucleated giant cells, and eosinophils (Panciera et al., 1992). Post-mortem findings showed severe bronchitis with pneumonia, yellow-brown liver, and inflamed forestomachs (Panciera et al., 1992; Cooper et al., 1984). Poisoning has been reported in one horse grazing hairy vetch: symptoms included oedema, especially around the lips and eyes, conjunctivitis and corneal ulceration (Anderson et al., 1983). In poultry, a diet containing 30-80% hairy vetch seeds caused a mortality rate of 20-40% (Cooper et al., 1984).
However, in practice, hairy vetch forage is often fed to ruminants. In an attempt to induce the disease in 3-year old Hereford cattle by including 100% hairy vetch in the diet for 5 weeks, no signs of morbidity or mortality were seen. Animals older than 3 years may be more susceptible to the disease, which could be due to an acute reaction following a previous contact with the plant (Panciera et al., 1992). In the case of horse poisoning reported above, only one horse out of the 8 grazing hairy vetch was ill, and there were no previous reports of horse poisoning (Anderson et al., 1983).
Feed intake reduction
Hairy vetch was found to contain L-canavanine, an amino acid that protects plants from predators but also reduced feed intake in pigs (Enneking et al., 1993).