A study was conducted to evaluate the effects of adding Rovabio Max™, an exogenous enzyme containing xylanase, $-glucanase, pectinase, mannanase, phytase and "-galactosidase activity to broiler diets with normal or reduced nutrient levels. Positive control diets for 0-3 wk and 3-6 wk were prepared based on NRC (1994) recommendations with Lys adjusted to 1.2% for 0-3 wk and 1.1% for 3-6 wk. These diets were formulated with or without the addition of 20% Distillers Dried Grains with Solubles (DDGS) of known composition. Reduced nutrient diets were prepared by reducing dietary metabolizable energy by 40 kcal/lb (88 kcal/kg), Ca by 0.10% and available P by 0.12% (EPC) and by an additional reduction of 5% in essential amino acids (EPC+AA). All diets were then fed with or without the addition of Rovabio Max™ at 200 g/ton as suggested by the manufacturer. Each diet was fed to four pens of 60 male birds of a commercial strain (Cobb 500) maintained in litter floor pens. Birds were weighed and feed consumption determined at 21 and 42 d of age. Two birds per pen were killed and tibia ash determined at 21 and 42 d; five birds per pen were killed at 42 d to determine carcass dressing percentage and parts yield. Birds fed the EPC diets did not differ significantly from those fed the positive control diet for body weight, mortality, tibia ash, dressing percentage, or breast meat yield at any point in the study. Additional reduction in amino acid content of the diets (EPC+AA) resulted in a significant decrease in 42 d body weight and a reduction in 21 d tibia ash compared to birds fed the positive control diet. Numerical differences in feed conversion were observed for both levels of nutrient reduction but not commensurate to the reduction in dietary energy content. Therefore, response to any exogenous enzyme might be expected to be minimal. The only positive response to the addition of Rovabio Max was a significant improvement in 21 d tibia ash, due to the phytase activity of the
