STABILITY OF FEED ENZYMES TO STEAM PELLETING DURING FEED PROCESSING

A barley-based diet for broiler chickens was supplemented with a comme rcial feed enzyme product (Avizyme SX(R), containing Trichoderma longi brachiatum beta-glucanase) at 0, 1 and 10 g kg-1 and pelleted after co nditioning 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-gl ucanase 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 tr eatment 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 c ontrol mash diets to 66% of initial activity, whereas 15 min condition ing 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-d egrees-C, these were 16% and 11%, respectively. There was a negative q uadratic effect of conditioning temperature and a positive linear effe ct of enzyme level on liveweight gain and feed efficiency. Conditionin g time did not influence chick performance and there were no treatment effects on feed intake. The incidence of vent pasting decreased linea rly with increasing enzyme inclusion rates and was significantly highe r after conditioning for 15 min compared with 30 s. Dietary beta-gluca nase 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 correla ted linearly with viscosity, which in turn correlated highly with bird performance. Despite this, dietary beta-glucanase values required tra nsformation to their logarithms before they could be used to accuratel y predict bird performance. The results from this experiment suggest t hat partial enzyme inactivation occurs at pelleting. The magnitude of the inactivation depends on the pelleting conditions employed, with hi gher temperatures and prolonged conditioning times increasing inactiva tion. How ever, in this experiment, bird performance was only affected when feeds were pelleted at temperatures over 85-degrees-C. The visco simetric method used for measuring beta-glucanase activity in the feed s proved to give a good estimate of the in vivo activity based on dige sta viscosity. However, values obtained with this method needed a loga rithmic transformation for accurate prediction of chick performance, t hereby reducing sensitivity with values normally encountered in feed. Digesta viscosity was a good indicator of bird performance.