Date of Graduation


Document Type


Degree Type



Davis College of Agriculture, Natural Resources and Design


Animal and Nutritional Sciences

Committee Chair

Joseph M. Moritz.


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, 93°C). Dietary treatments consisted of nutritionally adequate diets or Positive Control (PC), diets reduced in metabolizable energy (ME) and available phosphorous (AP) or Negative Control (NC), and NC diets with the exogenous enzyme. Study 1 established significant differences between the PC and NC diets (P<0.05). However, the exogenous enzyme cocktail did not improve performance. Study 2 was designed to improve the opportunity for the exogenous enzyme cocktail to demonstrate a benefit. This study utilized increased mixer-added fat 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 (P0.05). In Study 3, diet formulations were similar to Study 2; however, conditioning temperatures were decreased (71, 77, 82°C), a thinner die was used for pelleting and an additional unconditioned mash (UCM) treatment was added. Enzyme efficacy was demonstrated for live weight gain and feed conversion ratio (FCR) for UCM (P<0.05) as well as FCR for the 82°C diets (P=0.07). Performance observations in Study 3 were supported by nitrogen corrected apparent metabolizable energy (AMEn) data. Overall, these studies suggest that future evaluations of enzyme cocktail thermostability and subsequent efficacy should consider several manufacturing variables.