STABILITY OF FEED ENZYMES TO STEAM PELLETING DURING FEED PROCESSING

A barley-based diet for broiler chickens was supplemented with a commercial feed enzyme product (Avizyme SX(R), containing Trichoderma longibrachiatum beta-glucanase) at 0, 1 and 10 g kg-1 and pelleted after conditioning at 75, 85 or 95-degrees-C for either 30 s or 15 min in a 3 X 3 X 2 factorial design. The pelleted feeds were analysed for beta-glucanase activity, starch, total and soluble beta-glucan and non-starch polysaccharides (NSP) and fed to 1-day-old male broiler chickens for a 19 day period, at the end of which, weight gain, feed intake and the incidence of vent pasting were recorded. On Day 19, four birds per treatment were killed and digesta viscosity and beta-glucanase activity in the proximal part of the small intestine evaluated. Conditioning at 75-degrees-C for 30 s reduced beta-glucanase activity compared with control mash diets to 66% of initial activity, whereas 15 min conditioning at 75-degrees-C reduced recovery to 49%. At 85-degrees-C with 30 s and 15 min conditioning, the recoveries were 56% and 31%, and at 95-degrees-C, these were 16% and 11%, respectively. There was a negative quadratic effect of conditioning temperature and a positive linear effect of enzyme level on liveweight gain and feed efficiency. Conditioning time did not influence chick performance and there were no treatment effects on feed intake. The incidence of vent pasting decreased linearly with increasing enzyme inclusion rates and was significantly higher after conditioning for 15 min compared with 30 s. Dietary beta-glucanase correlated linearly with digesta beta-glucanase activity and the slope of the relationship indicated full recovery of the enzyme in the small intestine of the birds. Digesta beta-glucanase activity correlated linearly with viscosity, which in turn correlated highly with bird performance. Despite this, dietary beta-glucanase values required transformation to their logarithms before they could be used to accurately predict bird performance. The results from this experiment suggest that partial enzyme inactivation occurs at pelleting. The magnitude of the inactivation depends on the pelleting conditions employed, with higher temperatures and prolonged conditioning times increasing inactivation. How ever, in this experiment, bird performance was only affected when feeds were pelleted at temperatures over 85-degrees-C. The viscosimetric method used for measuring beta-glucanase activity in the feeds proved to give a good estimate of the in vivo activity based on digesta viscosity. However, values obtained with this method needed a logarithmic transformation for accurate prediction of chick performance, thereby reducing sensitivity with values normally encountered in feed. Digesta viscosity was a good indicator of bird performance.