Purdue University Graduate School
Tanner Wise_ Dissertation_ Spring 2024 - With Committee edits.pdf (1.25 MB)

Effects of exogenous enzymes on dietary nutrient digestibility for broiler chickens and growing pigs

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posted on 2024-04-24, 17:03 authored by Tanner L WiseTanner L Wise

The objective of the experiments conducted for this dissertation was to investigate the effects of exogenous enzymes on nutrient digestibility for broiler chickens and growing pigs. These experiments covered the effects of phytase, protease, and carbohydrases on the nutrient availability of various diet types and ingredients, as well as evaluations of regression methods for determining ingredient energy values. One study investigated a factorial of phytase and dietary phytate levels on the ileal digestibility of amino acids (AA) and phosphorus (P) for broilers and pigs. The results of these experiments indicated that phytase improved the ileal digestibility of P (P < 0.05) and all AA (P < 0.05) for broilers regardless of the dietary phytate level, and the ileal digestibility of P (P < 0.05) and many economically important AA (P < 0.05) for pigs. This study did not reveal any significant interactions between phytase and dietary phytate, but there were a number of numerical differences in the relative effect of phytase in the two diet types. In a subsequent experiment the effects of a factorial of phytase and protease on ileal P and AA digestibility were evaluated for growing pigs. Similarly to the first study, phytase was shown to improve the ileal digestibility of P (P < 0.05) and a majority of AA (P < 0.05). There were limited main effects of protease, however, it was found to decrease the digestibility of Lys, Met, and Thr (P < 0.05). There were a number of significant quadratic interactions (P < 0.05) of protease within phytase level, where the necessary concentration of protease to elicit positive effects was dependent on phytase inclusion. The next study evaluated the effects of two carbohydrase blends on the ileal AA digestibility and energy values of soybean meal. Both enzyme blends elicited modest improvements in the ileal and total tract digestibility of energy, but there were limited effects on the energy values of the test diets. Both enzyme blends improved the apparent metabolizable energy of soybean meal, but the blend with lower activity and no protease inclusion produced the greater results with an improvement of 15.2%. These enzyme blends resulted in the improved ileal digestibility of nearly all AA from soybean meal for broilers. The last study was a validation of the three-point model for the regression method against a four-point model over both the same test ingredient inclusion range or smaller range. This evaluation used both canola meal and wheat as test ingredients to evaluate if changes in dietary energy or protein levels affect the results of this method, which are representative of both cereal grains and protein concentrates, respectively. The results indicated that there was no difference in the three and four-point models for either ingredient as long as the overall range of test ingredient concentration was the same in both models. This proved more important for canola meal, as it was more susceptible to problems with the estimates or variability based on changes in inclusion. Based on the results of these experiments, it is clear that phytase can improve the AA digestibility for both pigs and chickens, but care must be taken when combinations are made with protease. These data indicate that the use of carbohydrase blends can improve the nutrient availability of soybean meal, and this could have significant implications in diet formulation. Lastly, the use of the three-point model for the regression method is appropriate, but is dependent on the inclusion level of the test ingredient test ingredient.


Degree Type

  • Doctor of Philosophy


  • Animal Sciences

Campus location

  • West Lafayette

Advisor/Supervisor/Committee Chair

Olayiwola Adeola

Additional Committee Member 2

Darrin Karcher

Additional Committee Member 3

Brian Richert

Additional Committee Member 4

Michael Kidd

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