Nonruminant Nutrition: Enzymes 1

Feed ingredient price has influenced nutritionists to maximize diet nutrient availability through use of exogenous enzymes. Poultry are almost exclusively fed pelleted diets that entails feed being subjected to conditions of high moisture, temperature and pressure that could partially denature added enzymes. Exogenous enzyme efficacy may be decreased or completely lost if enzymes are not able to survive the pelleting process. The objective of the current studies was to properly assess the efficacy of a commercially available exogenous enzyme cocktail subjected to increasing steam conditioning temperatures during pelleting (82, 88, 93oC). All studies used male Cobb 500 broilers obtained from the same commercial hatchery. The experimental period was from d 3–21 with 8 birds per pen and 8 replications per treatment. Study 1 established significant differences between the Positive Control (PC) and Negative Control (NC) diets (P < 0.05). However, the exogenous enzyme cocktail did not show improved performance. Study 2 was designed to improve the opportunity for the exogenous enzyme cocktail to demonstrate a benefit. This study utilized increased mixer-added lipid addition in the diet formulation that may decrease frictional heat production in the pellet die, and a decreased metabolizable energy difference between the positive and negative control. Again, performance differences were observed between the PC and NC control diets (P < 0.05), with no beneficial effect demonstrated for the exogenous enzyme at any temperature (P > 0.05). In Study 3, diet formulations were similar to Study 2; however, temperatures were decreased (71, 77, 82oC) and an additional unconditioned mash (UCM) treatment was added. Significant differences were obtained between NC diets with and without exogenous enzyme cocktail in the UCM for live weight gain and feed conversion ratio (FCR) and at 82oC for FCR (P < 0.05). However, only numerical differences in performance were shown between the PC and NC diets.