Effects of a xylanase and protease, individually or in combination, and an ionophore coccidiostat on performance, nutrient utilization, and intestinal morphology in broiler chickens fed a wheat-soybean meal-based diet.

The effects of 2 single exogenous and monocomponent feed enzymes, and their combination, and an ionophore coccidiostat on production performance, feed AME(n), nutrient utilization, and intestinal morphology were studied in broiler chickens. One-day-old unvaccinated and unsexed Ross 308 birds (n = 320) were kept in groups of 8 on wood shavings in pens raised from the floor and fed one of 5 experimental diets, replicated 8 times, for 36 d. Treatments were 1) a wheat-soybean meal-based feed with no added coccidiostats or exogenous enzymes (CON), 2) CON + ionophore coccidiostat (Narasin), 3) CON + xylanase (Ronozyme WX CT; XYL), 4) CON + serine protease (Ronozyme ProAct CT; PRO), or 5) CON + xylanase + serine protease (XYL+PRO). Enzymes were added on top in the feed formulation. Diets contained 0.5% TiO₂ to facilitate estimations of total tract apparent nutrient utilization. Treatments had no effect on BW gain or feed intake, but feed conversion, apparent digestibility of starch and fat, and feed AME(n) were improved with all enzyme treatments. The relative length of the ileum was reduced with XYL+PRO. For all parameters measured, the effects of XYL+PRO were similar to when XYL and PRO were fed individually. Narasin had no effect on production performance or nutrient utilization but reduced the relative lengths of jejunum and ileum. Relative lengths and weights of duodenum and cecum were unaffected by treatments. In conclusion, the improved feed conversion with both a xylanase and a protease was reflected in increased nutrient utilization, but their combination was not superior to when supplied separately. Narasin did not affect performance or nutrient utilization but reduced the relative lengths of the jejunum and ileum.