NUTRITIONAL EVALUATION AND IMPROVEMENT OF SHEA NUT (Vitellaria paradoxa, Gaertn.) MEAL FOR POULTRY

Abstract

Shea nut (Vitellaria paradoxa, Gaertner or Butyrospermum parldi, Kotschy) meal, a solid residue from the shea fat industry, is available in large quantities in West Africa. Six collected samples (2 non-industrial and 4 industrial or expeller meals) had a range of nutrient compositions [g/kg dry matter (DM) basis] of crude protein (CP) (103.9 - 143.6) with low concentrations of lysine (30.0 - 41.7 g/kg CP) and methionine plus cystine (33.4 - 39.7 g/kg CP); ether extract (101.4 - 394.8), ash (46.9 - 75.6) and total non-starch polysaccharides (NSP) (305.9 - 396.6) as well as gross energy (22.8 - 27.4 MJ/kg DM). A major part of the variability was due to the large differences in the amounts of residual fat. A broiler bioassay indicated that shea fat had a low metabolisable energy (22.0 MJ/kg DM) compared to soybean oil (39.8 MJ/kg DM). Also, two broiler bioassays showed that the shea nut meals had low energy availability as indicated by their low TMEn values (12.6 - 15.5 MJ/kg DM). Another broiler assay showed that the mean nutrient utilisation efficiencies of the meals were relatively low for dry matter (0.645), crude protein (0.585) and lipid (0.665). The major anti-nutritive factors identified were saponins (4.0 - 6.3 g/kg DM) and tannins (35.1 - 201.3 g/kg DM). There was no evidence of theobromine being present in any of the six samples. There was a strong negative correlation (P<0.05) between dry matter metabolisability and total NSP content of the meal. A broiler growth experiment showed that there was a quadratic decline (P<0.001) in feed intakes, growth rates and feed conversion efficiencies when shea nut meal was included at increasing dietary levels in nutritionally complete diets. The untreated shea nut meal can be fed at 20 g/kg in a broiler diet. However, the treatments of the shea nut meal by hot water extraction, natural fermentation with added polyethylene glycol, and fermentation using either Aspergillus niger or a mix of Bacillus subtilis and Bacillus licheniformis gave improvements (P<0.001) in the growth rates of broiler chickens when incorporated at 90 g/kg in the diets. A fungal fermentation using A. niger and Ceriporiopsis subvermispora was further investigated. The treated meals gave increased (P<0.001) broiler growth rates compared to the untreated meal when incorporated at 90 g/kg. Combinations of both fungal organisms or with polyethylene glycol gave no further improvement (P>0.05) in growth performance. Another bioassay that involved shea nut meal fermentation using A. niger and C. subvermispora confirmed their potential in improving its nutritional value to broiler chickens. The experiment also showed that the fungal fermentation process should, in preference, be completed in a closed container in order to avoid contamination by other organisms. The A. niger fermentation process resulted in substantial reductions in the concentrations of saponin (86.7%), total proanthocyanidins (34.5%) and hydrolysable tannins (52.9%). Another broiler growth experiment that examined the effect of defatted shea nut meal fermentation using A. niger showed there was no significant difference in growth performance between 'as-received' and defatted meals. A. niger fermentation of shea nut meal improved (P<0.001) the growth rates of broiler chickens when the fermented meals were included at 100 g/kg in the diets in comparison to the unfermented meal, but the growth rates obtained were lower (P<0.001) than for the birds fed the control diet. It was evident from this study that the untreated shea nut meal has a low nutritive value that can be improved through fermentation, particularly using A. niger. The nutritional improvement of shea nut meal achieved in this study still falls far short of what is expected for it to become valuable for the poultry feed industry. These fermentation methods using A. niger or C. subvermispora require further improvements to provide satisfactory feed products