An effective combination of carbohydrases that enables reduction of dietary protein in broilers: importance of hemicellulase.

ABSTRACT

After observing the effects of purified cellulase (C), hemicellulase (H), pectinase (P), and their combinations on the in vitro digestibility of a corn-soybean meal broiler diet, we examined the associations between pectin breakdown and the digestibilities of CP and DM by using free galacturonic acid (GA) as an index of pectin breakdown. There was no significant effect of the single enzymes except for H. However, the enzyme combinations H + P, C + H, and C + H + P significantly increased CP and DM digestibilities, whereas the combination of C + P was not effective. Because H has activities of both H and P, these enzymes were considered to be important in stimulating digestion. Furthermore, when the enzymes increased CP and DM digestibilities, GA concentration was significantly higher, and clear correlations between CP and DM digestibilities and GA concentration were observed, whereas correlations between the digestibilities and concentration of glucose or xylose + mannose as indices of cellulose and hemicellulose breakdown, respectively, were not significant. From these observations, we hypothesized that a mixture of enzymes could increase the protein digestibility of broiler feed. Thus, in the in vivo experiment, low-protein (19% CP) diets made mainly of corn and soybean meal with or without mixed enzymes were prepared and given to broiler chicks. The birds given the diet containing mixed enzymes showed significantly higher BW gain, with higher CP and DM digestibilities than the birds given the diet without the mixed enzymes. Moreover, the growth rate was same as that of the birds given the normal (21% CP) diet. The results indicate that the mixed enzyme preparation can effectively degrade indigestible cell constituents and thus enable the protein of the broiler feed to become more digestible. Furthermore, the results indicate the importance of H as a rate-limiting factor of cell wall breakdown.