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A total of 210 pigs (initially 13.6 lb) were used in the 35-d experiment to evaluate the effect of increasing levels of Natuzyme^� (0, 0.035, and 0.05%) on weanling pig performance. Natuzyme^� was added to either a negative or positive control diet as a 2 x 3 factorial to form six dietary treatments. The negative control diet was a corn-soybean meal based diet containing 12.5% soy hulls and no antibiotics. The positive control diet was higher in energy without the soy hulls and contained a feed-grade antibiotic (Neo-Terramycin with 140 g of neomycin and 140 g of oxytetracycline per ton). Pigs were blocked by weight and randomly allotted to treatment at weaning. Diets were fed in two phases from d 0 to 14 and d 14 to 35. For d 0 to 14, ADG and average wt on d 14 tended to improve (P=0.08) by feeding the positive control diets with a feed-grade antibiotic. There were also trends for quadratic (P=0.09) improvements in ADG, ADFI, and average wt on d 14 with the addition of Natuzyme^� at 0.035 and 0.05%. For the overall trial (d 0 to 35), ADG and average wt on d 35 tended to be increased for pigs fed Natuzyme^� (linear, P=0.09; and quadratic, P=0.07; respectively) and for pigs fed the positive control diets (P=0.07 and P=0.08, respectively) compared with pigs fed the negative control. In conclusion, the growth performance of pigs fed the positive control diets containing a feed-grade antibiotic was only slightly better than the performance of pigs fed the negative control diets containing soy hulls. The addition of Natuzyme^� to corn-soybean meal-based diets may improve pig performance, particularly in the positive control diets containing a feed-grade antibiotic. In this study, there did not appear to be a benefit to feeding more than 0.035% Natuzyme^�.

(Key Words: Pigs, Energy, Soy Hulls, Enzymes, Feed-Grade Antibiotics)