Many Lathyrus species are implicated in a paralysis of humans and animals known as lathyrism, which has different causes and symptoms depending on the Lathyrus species involved (Hanbury et al., 2000). In the case of Lathyrus sativus, the seeds and vegetative parts contain a neurotoxic non-protein amino acid, ß-oxalyl-L-a,ß-diaminopropionic acid (ODAP or BOAA). The ingestion of ODAP causes neurolathyrism, a neurodegenerative disease that damages upper motor neurons, causing irreversible paralysis of the lower limbs and sometimes death in humans and animals (Spencer et al., 1983). The susceptibility of humans to this particular form of lathyrism varies with their nutritional status, age and health. Lathyrism is more severe in people lacking Zn (Hanbury et al., 2000). Because grass pea is a hardy, drought-resistant legume, it tends to be consumed in excess when there is a lack of alternative food sources, due to poverty, war or drought, with devastating impact. In Ethiopia, an outbreak of lathyrism occurred in 1997, crippling 2000 people (Getahun et al., 1999). During the 20th century, outbreaks occurred in Afghanistan, Algeria, China, France, Germany, Italy, Pakistan, Romania, Russia, Spain and Syria (Hanbury et al., 2000).
Ruminants and monogastric animals are sensitive to ODAP in varying degrees and the scientific literature is somewhat contradictory. Horses are noted as being very susceptible to lathyrism, following heavy grazing or feeding on grass pea seeds, with symptoms of paralysis of the hind limbs and death resulting in some cases. There is anecdotal evidence of pigs, sheep and cattle having died due to lathyrism after being turned into Lathyrus sp. fields (Hanbury et al., 2000). Horses, donkeys, goats and sheep developed spasticity in the hind limbs after feeding on Lathyrus sativus grain for between 1 and 3 years (Tekle Haimanot et al., 1997 cited by Hanbury et al., 2000). Poultry feeding trials (Latif et al., 1975; Low et al., 1990) and pig trials (Castell et al., 1994) have reported a decrease in performance after feeding grass pea seeds, though without noting any toxic effects. However, feeding trials with sheep, calves, piglets and donkeys failed to demonstrate signs of lathyrism and effects on animal performance (though liver and kidney cells underwent pathological changes in one study) (Budag et al., 2009; Dhiman et al., 1983; Yan et al., 2006). In ruminants, there is some evidence that rumen microorganisms can adapt to ODAP and may destroy most of the toxin (more than 90% in 4-5h) (Farhangi, 1996 quoted by Hanbury et al., 2000; Marichamy et al., 2005).
ODAP levels are highly variable and depend on variety, growth location, soil, fertiliser levels, plant part and age (Gurung et al., 2011; Jiao et al., 2006; Jiao et al., 2011). In a survey of over 100 accessions from various countries, the ODAP content in grass pea seeds varied from 0.2 to 7.2 g/kg DM (Deshpande et al., 1992). In Ethiopia, other studies reported ODAP content in seeds varying from 5.4 to 8.9 g/kg DM (Urga et al., 2005) or 2.0 to 4.5 g/kg DM (Denekew et al., 2009). The green parts and the straw contain lower concentrations of ODAP: 1.9 to 3.4 and 1.3 to 2.1 g/kg DM respectively (Denekew et al., 2009).
Processing can detoxify grass pea seeds. Steeping and boiling decreased ODAP levels by 90% (Padmajaprasad et al., 1997), while extrusion reduced ODAP levels by 46% (Ramachandran et al., 2004).
Others antinutritional factors
Grass pea contains trypsin and chimotrypsin inhibitors, amylase inhibitors, lectins, tannins, phytates and oligosaccharides. Except for ODAP, most of these antinutritional factors are in lower quantities in grass pea than in other legumes and are unlikely to cause serious concern when it is fed to animals, though they may depress performance (Hanbury et al., 2000).