β-Mannan is a polysaccharide commonly found in feed ingredients such as soybean meal, palm kernel meal, copra meal, and sesame meal. Due to the almost universal use of soybean meal (SBM) and full fat soy as protein sources in poultry feeds, β-Mannans are present in the overwhelming majority of current poultry rations used around the world. β-Mannan, also referred to as β-galactomannan, is a polysaccharide with repeating units of mannose, with galactose and/or glucose often found attached to the β-Mannan backbone. The solubility of β-Mannan in water increases as the number galactose or glucose molecules on the mannan backbone increases. Guar gum and guar meal also contain high levels of β-Mannan. The β-Mannan in guar gum has an average galactose to mannose ratio of 1:1.7, which is similar to the average ratio of 1:1.8 in SBM. Studies (1, 2, 3) have shown that β-Mannans are capable of stimulating the innate immune system, with a resulting increase in proliferation of macrophages and monocytes, and increased cytokine production, leading to an increased severity of disease symptoms and a decrease in the efficiency of nutrient utilization. Moreover, Dendritic cells, which have surface mannan receptors (4) have been shown to pry open tight junction between epithelium cells and, then, move into lumen to sample surrounding lumen antigens (5). This may provide a way of contact between immune cells and lumen β-Mannan from soy. β-Mannans have been found to be highly deleterious to animal performance, severely compromising weight gain and feed conversion (6), as well as glucose and water absorption (7). Nunes and Malmlof (8) confirmed the negative effect of β-Mannan on glucose absorption, along with decreases in apparent production of insulin, glucagon, and IGF-1. More recently the beneficial effect of enzymatic degradation of β-Mannan by addition of β-Mannanase to diets containing SBM has been documented in broilers (9, 10, 11), layers (12, 13), turkeys (14) and swine (15). Jackson et al. (16) found the addition of β-Mannanase to improve the performance of chicks experimentally inoculated with Eimeria sp. and Clostridium perfringins.

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