While proximate composition of velvet bean seeds makes it tempting to use it in poultry diets, the presence of antinutritional factors limits their practical interest, unless appropriate technological treatments are found (Carew et al., 2006).
Broilers, quails and Guinea fowls
Raw mucuna seeds should be avoided in broilers. Processed seeds (by dry roasting or soaking+boiling) can be included up to 10 %, with an adapted feed formulation, but even processed seeds should be used carefully and probably avoided in starter animals.
Performance is strongly degraded in broilers fed raw mucuna (Harms et al., 1961; Ferriera et al., 2003; Emiola et al., 2007; Emenalom et al., 2005b; Tuleun et al., 2008a). Degradation can occur at low incorporation levels: 5 % raw velvet bean can induce a 25 % drop in animal performances (Iyayi et al., 2006b). Significant mortality can be registered at high levels (Harms et al., 1961; Del Carmen et al., 1999). The effect is similar in Guinea fowl (Dahouda et al., 2009a). Velvet bean seems to be more detrimental to growth than to feed intake, although results differ among authors (Trejo et al., 2004; Emiola et al., 2007; Tuleun et al., 2008a, etc.). The feed conversion ratio is always strongly degraded.
Technological treatments, and particularly heat treatments, can help to reduce the negative effects of velvet bean (Carew et al., 2006). However, performance is seldom completely restored compared to control diets even if differences can be statistically non significant at lower inclusion rates. The main treatments that have been tested include: soaking (with or without additives in water), boiling, autoclaving, dry roasting and combinations of these techniques. These treatments help to decrease the levels of antinutritional factors such as antitrypsic factors, L-dopa, tannins and hemagglutination factors (Vadivel et al., 2011).
Dry roasting has been found to be an efficient way to limit the negative effects of velvet bean in broilers but also in Japanese quails (Del Carmen et al., 1999; Emiola et al., 2007; Ukachukwu et al., 2007b; Tuleun et al., 2009a). However some authors compared various treatments and found roasting less efficient than boiling in broilers and in Guinea fowls (Emenalom et al., 2005b; Dahouda et al., 2009a).
Regarding wet treatments, soaking alone (in water with ou without additives) is not efficient (Nyirenda et al., 2003; Tuleun et al., 2010b; Vadivel et al., 2011) and soaking should be combined to a heat treatment such as boiling or autoclaving. The duration of thermal treatments can have an effect: boiling velvet bean seeds for 20 min resulted in lower growth performance than 40 or 60 min (Tuleun et al., 2008a). For several authors, the optimal treatment consists in soaking (in water or Na bicarbonate) followed by boiling (60 to 90 min) and drying. This procedure was found to eliminate antinutritional factors efficiently (Vadivel et al., 2011) and allows to maintain performances up to 10-20% inclusion (Ukachukwu et al., 2003; Akinmutimi et al., 2006; Emenalom et al., 2006; Ukachukwu et al., 2007a; Ani, 2008; for Guinea fowls, Farougou et al., 2006). However, even roasted and soaked+boiled seeds can degrade performances at low inclusion rates (6-10 %) (Emenalom et al., 2005a; Iyayi et al., 2003; Vadivel et al., 2011).
Thermal treatment also improved protein digestibility, probably by inactivation of the antinutritional factors: for example 1 h dry exposure at 100°C increased protein digestibility from 65 % to 74 % (Iyayi et al., 2008).
The metabolizable energy value of velvet bean seeds varies with the process:
Laying hens and quails
Using velvet bean seeds, even when processed, is not recommended in commercial egg production though economic considerations may make them profitable.
The use of raw velvet bean seeds in layer diets causes a strong degradation of performance. Daily egg production dropped from 78.5 % to 65.5 % with 12.5 % of raw seeds (Harms et al., 1961) and from 84 % to 38 % with 20 % of raw seeds (Tuleun et al., 2008b).
Technological treatments reduce the negative effects of velvet bean seeds, but do not enable the same performances as the control diets: in laying hens, the best treatment (toasting) allowed 74 % hen-day egg production vs 84 % in the control with 20 % velvet bean seeds, while boiled seeds yielded 59 % hen-day egg production (Tuleun et al., 2008b). In laying Japanese quails, 15 % of toasted seeds caused a significant degradation of the performances, but the lower feed cost per egg produced and feed cost per bird made using velvet bean seeds profitable (Tuleun et al., 2010b). Egg composition and quality were not affected by the inclusion of velvet bean seeds (Iyayi et al., 2003; Tuleun et al., 2008b).