1,3-1,4-β-Glucanases and not 1,4-β-glucanases improve the nutritive value of barley-based diets for broilers

Abstract

Barley-based diets contain a significant proportion of highly soluble 1,3-1,4-β-glucans that display anti-nutritive properties for monogastric animals, in particular for poultry. Cleavage of mixed linked glucans by the addition of exogenous enzymes leads to a significant reduction in the degree of polymerization of the polysaccharide and a consequent reduction of digesta viscosity. Plant cell wall 1,3-1,4-β-glucans may be hydrolyzed by 1,3-1,4-β-glucanases (EC 3.2.1.73) or by 1,4-β-glucanases (EC 3.2.1.4), generally termed cellulases, although it remains unknown which enzymes are more effective in the degradation of feed mixed linked anti-nutritive glucans. Here we compared the capacity of two recombinant Clostridium thermocellum enzymes, 1,3-1,4-β-glucanase 16A (CtGlc16A) and 1,4-β-glucanase 8A (CtCel8A), to improve the nutritive value of barley based diets for broilers. As already shown in a previous study (Ribeiro et al., 2012), CtGlc16A is very effective to improve the performance of broilers fed with a highly viscous barley-based diet. In contrast, although remaining active and retaining its molecular integrity during passage through the GI tract, CtCel8A was unable to affect the nutritive value of the cereal based diet. In vitro studies revealed that CtGlc16A and CtCel8A are equally effective in reducing the viscosity of a purified 1,3-1,4-β-glucan solution. However, the capacity of CtCel8A to cleave 1,3-1,4-β-glucans is significantly affected by the presence of the barley-based feed. Taken together the results suggest that in vivo 1,4-β-glucanases tend to act preferentially on cellulosic substrates and not on mixed linked glucans. Although further work is required to extend these observations to other cellulases, the data suggest that exogenous 1,3-1,4-β-glucanases but not 1,4-β-glucanases are obligatory enzymes to improve the nutritive value of barley based diets for broilers.