Most toxicological problems with velvet bean are due to its seeds.
L-dopa
Velvet bean seeds and, to a smaller extent stems and leaves, contain two important non-protein amino-acids: L-dopa from which dopamine, a potent anti-Parkinson disease agent, is prepared, and DMP (dimethyltryptamine), an hallucinogenic substance. L-dopa content varies from 1.6 to 7% (Cook et al., 2005; Wulijarni-Soetjipto et al., 1997). Ensiling decreased L-dopa content in the seeds by 10-47% (Matenga et al., 2003).
L-dopa is a potent antinutritional factor (Siddhuraju et al., 2002) and may cause severe vomiting and diarrhoea in pigs fed large quantities of velvet bean seeds. It is less harmful in ruminants: it does not appear to modify rumen fermentation and there is a rumen microbial adaptation to L-Dopa (Chikagwa-Malunga et al., 2009b). Trials in sheep and goats fed velvet beans and pods did not find that L-dopa had any adverse effects (Matenga et al., 2003; Castillo-Camaal et al., 2003a; Pérez-Hernandez et al., 2003; Castillo-Camaal et al., 2003b; Mendoza-Castillo et al., 2003).
Alkaloids
Velvet bean seeds contain a number of alkaloids, notably mucunain, prurienine and serotonin. Mucunain is produced by pod hairs. It causes severe itching to the skin, and the hairs coming in contact with the eyes can be very painful. L-dopa may also be implicated in skin eruptions (Pugalenthi et al., 2005). The negative effects of mucunain are potentialized by serotonin (Cook et al., 2005). It has been reported that haemorrhage and death can result from cattle eating the hairy pods (Miller, 2000). Pod hairs have the same anthelmintic efficacy as piperazine against ascariasis in buffalo calves (Behura et al., 2006).
Other antinutritional factors
Velvet bean seeds contain other antinutritional factors:
Trypsin and chymotrypsin-inhibiting activities decrease protein digestibility, induce pancreatic hypertrophy and hyperplasia, increase trypsin secretion and, therefore, reduce N retention, growth and feed conversion (Pugalenthi et al., 2005; van Eys et al., 2004; Rackis et al., 1986).
Phytate content is relatively high in the seeds and may reduce mineral and protein availability (Pugalenthi et al., 2005).
Oligosaccharides (mainly verbascose) cause flatulence (Pugalenthi et al., 2005).
HCN is found in velvet bean seeds, but in amounts well below (5.8 mg/100g) the lethal dose (35 mg/100g) (Pugalenthi et al., 2005).
Lectins and saponins are also found (Pugalenthi et al., 2005).
These antinutritional factors can be efficiently reduced by a wide range of treatments (see Processes on the "Description" tab).