While proximate composition of velvet bean seeds makes it tempting to use them 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 velvet bean seeds should be avoided in broiler diets. Processed seeds (dry roasting or soaking + boiling) can be included at up to 10% of the diet with an adapted feed formulation, but even processed seeds should be used carefully and probably avoided for starter animals.
Performance is markedly reduced in broilers fed raw velvet beans (Harms et al., 1961; Ferriera et al., 2003; Emiola et al., 2007; Emenalom et al., 2005b; Tuleun et al., 2008a). This reduction can occur at low levels of incorporation: 5% raw velvet beans can induce a 25% drop in animal performances (Iyayi et al., 2006b). Significant mortality rates can be registered at high levels of inclusion (Harms et al., 1961; Del Carmen et al., 1999). The effects were similar in Guinea fowl (Dahouda et al., 2009a). Velvet beans appear 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 markedly reduced.
Treatments, and particularly heat treatments, can help to reduce the negative effects of velvet beans (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 antitryptic 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 beans in broilers and Japanese quails (Del Carmen et al., 1999; Emiola et al., 2007; Ukachukwu et al., 2007b; Tuleun et al., 2009a). However other 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 or without additives) is not efficient (Nyirenda et al., 2003; Tuleun et al., 2010b; Vadivel et al., 2011), therefore, it should be combined to a heat treatment such as boiling or autoclaving. The duration of thermal treatments can have an effect on their efficiency: boiling velvet bean seeds for 20 minutes resulted in lower growth rates than boiling for 40 or 60 min (Tuleun et al., 2008a). For several authors, the optimal treatment consisted of soaking in water or sodium bicarbonate, followed by boiling (60 to 90 min) and drying. This procedure was found to eliminate antinutritional factors efficiently (Vadivel et al., 2011) and broiler performance was maintained at up to 10-20% inclusion of velvet beans in the diet (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 reduce performance 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, as shown in the table below:
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 can result in a marked reduction in performance. Daily egg production dropped from 78.5% to 65.5% with 12.5% raw seeds in the diet (Harms et al., 1961), and from 84% to 38% with 20% inclusion (Tuleun et al., 2008b).
Treatment reduce the negative effects of velvet bean seeds, but did not enable the same performance as control diets with lower levels of velvet bean seeds: in laying hens, the best treatment (toasting) allowed 74% hen-day egg production vs. 84% from the control diet with 20% velvet bean seeds, while boiled seeds yielded 59% hen-day egg production (Tuleun et al., 2008b). In laying Japanese quails, 15% toasted seeds caused a significant reduction in performance, but the lower feed cost per egg produced, and feed cost per bird, justified using velvet bean seeds (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).