Date of Graduation


Document Type


Degree Name

Doctor of Philosophy in Poultry Science (PhD)

Degree Level



Poultry Science


Susan E. Watkins

Committee Member

Michael Kidd

Second Committee Member

Craig Coon

Third Committee Member

Charles Rosenkrans


Broilers, Phytase, Phytate, Super-dosing


Two trials were performed using one-day-old male Cobb x Cobb 500 broilers to determine how dietary phytate and phytase levels as well as phytase phase feeding impacted bird performance parameters, tibia characteristics, and malonaldehyde (MDA) content of the liver, breast and thigh tissues. The first experiment consisted of 1,008 birds randomly placed in 48 floor pens within two commercial broiler houses at the Applied Broiler Research Farm (ABRF; 21 birds per pen; 0.76 ft2 per bird). A 2 X 3 factorial design was used with two levels of dietary phytate (0.21 and 0.31 %) and three levels of phytase supplementation (0, 500 and 1,500 FTU/kg). Main effect phytase improved (P < 0.05) feed intake, body weight at 17 d, body weight gain and tibia ash weight and percentage. In addition, phytase and phytate interacted (P ≤ 0.011) for FCR and FCR corrected to the overall experimental mean for body weight (AFCR).

The second trial consisted of 1,056 total birds randomly placed in 48 floor pens within two commercial broiler houses at ABRF (22 birds per pen; 0.72 ft2 per bird). Treatments consisted of a positive control, a negative control (NC; less 0.16 % Ca, 0.15 % avP and 0.04 % Na), and four additional treatments based on the negative control. Treatments 3 and 4 consisted of the NC diet supplemented with 500 FTU/kg of phytase in the starter phase that was either continued through the grower diet (treatment 3) or increased to 1,500 FTU/kg (treatment 4). Treatment 5 and 6 were also the NC diet supplemented with 1,500 FTU/kg of phytase for the starter diet and either decreased to 500 FTU/kg in the grower diet (treatment 5) or maintained at 1,500 FTU/kg (treatment 6). A random complete block design was employed and analyzed using SAS GLM. At 35 d of age, phytase regimen did not affect (P > 0.05) feed intake, BW gain, FCR, AFCR or mortality. However, increasing phytase concentration from 500 FTU/kg in the starter diet to 1,500 FTU/kg in grower diet increased (P < 0.05) proximal and total tibia ash percentages when compared to broilers fed diets with 500 FTU/kg of phytase for the duration of the study.