Beta-mannans are a group of closely related heat-resistant compounds that survive the drying/toasting phase of soy bean processing. β-mannans comprise about 1.3% of the 48%-CP SBM product and 1.5-1.7% of the 44%-CP SBM product, with an estimated β-galactomannan content of 1.83% and 2.22%, respectively. Mannans, mainly associated with the hull and fibre fraction of SBM, are intensely antinutritional due to their highly viscous properties, likely decreasing the efficiency of the monogastric’s carbohydrate utilisation by partially blocking key sites on the intestinal surface and resulting in a lower performance. Beta-mannans’ effects can be reduced by the use of dietary mannanase enzymes (β-D-mannanase) which degrade some of these complex polysaccharides into smaller units, some of which can be utilised for energy production.
Approximately 40% of SBM is made up of crude fibre, and various polysaccharides and oligosaccharides. Stachyoses and raffinoses are non starch polysaccharides (NSP) that has anti-nutritional properties and are present in soya beans. Stachyose [Gal α(1-6)-Gal α-(1- 6)-Glu α-1-β-2Fru] and raffinose [Gal α-(1-6)-Glu α-1-β-2Fru] represent a significant amount of potential dietary energy present in SBM. However, the α-galactoside family of oligosaccharides has been implicated in reducing SBM true metabolisable energy (TMEn), fibre digestion, and transit time in chickens.
It has been well documented that the α–galactoside oligosaccharides are also a major cause of hydrogen gas production from SBM in poultry. Endogenous enzymes in poultry are specific for α-linked carbohydrates similar to that in starch, but they are not active against SBM oligosaccharides because the α-galactosides cannot be hydrolysed due to the lack of α-1,6 galactosidase activity in the intestinal mucosa. Consequently, undigested oligosaccharides pass to the distal end of the intestine where they are fermented by gut microflora to volatile fatty acids (VFA) and gases, thus yielding less energy and creating digestive disturbances. Raffinose and stachyose significantly reduced TMEn values of adult Leghorn roosters when added to the feed at levels equal to that normally found in SBM.
Dry matter digestibility also appears to be negatively affected thus, decreasing significantly as stachyose levels increase. However, stachyose and raffinose can be hydrolysed to glucose, galactose, or corresponding disaccharides in the proximal small intestine via supplementing the feed with an enzyme mixture containing the proper oligosaccharidase.
Mannanase enzymes are endo-hydrolyases that are typically fermentation products of Bacillus spp. This enzyme typically degrades β-Mannans present in feed. β-Mannanases cleave randomly within the 1,4-β-D-mannan main chain of alactomannan, galactugluco-mannan, and mannan. Since β-endo-mannosidases improve the digestibility of all types of mannan, and because a major source of mannan in soya is the hull, the effect of β-mannosidase seems to be more pronounced when supplemented to diets containing SBM-44, which contains hulls, as opposed to SBM-48. Use of mannanases in feed has increased over the last two decades, constituting almost 10% of the overall enzymes used in corn-SBM poultry diets globally.
The increased use of different feed ingredients requires the use of exogenous Pentosanases such as galactosidases, xylanases and glucanases. The use of such enzymes, either individually or in a blend, results in degrading the complex NSP and releasing other nutrients that might be bound or otherwise trapped within the complex net-like NSP. The use of these enzymes will result in liberating energy and limited amounts of proteins resulting in improving growth performance parameters in all types of poultry.