Date of Graduation


Document Type


Degree Name

Master of Science in Poultry Science (MS)

Degree Level



Poultry Science


Susan Watkins

Committee Member

Sami Dridi

Second Committee Member

Sam Rochell


Phosphorus Retention, Phytase, Tibia ash, Xylanase


Two 3-week experiments were conducted, each using 480 day-old male broilers placed randomly among 96 battery cages (5 per cage; 680cm2 per bird), to evaluate the influence of phytase supplementation, with or without supplemental xylanase, on bird performance. Individual body weights and cage feed weights were taken on days 0, 7, 14, and 21, and mean BW, body weight gain (BWG), feed intake (FI), and FCR over each period calculated. Mortality was recorded daily and used to calculate livability and adjust FCR in both trials. In trial 2, excreta was collected by cage from 14 to 21 days for bone ash analysis and left tibias were collected from each bird on day 21 to calculate phosphorus retention. Phosphorus-deficient basal diets for trials 1 and 2 were formulated to contain 0.875% Ca each and 0.13 and 0.18% available phosphorus (AvP), respectively. Using SAS, a 2 x 6 factorial arrangement with two levels of supplemental xylanase (0 and 1,500 EPU/kg) and six supplemental phytase levels (0, 100, 175, 250, 1,000, and 1,500 FTU/kg) was applied to a GLM procedure as well as to linear, quadratic, and cubic polynomial contrasts to evaluate all parameters.

Overall, phytase effects (P < 0.05; linear, quadratic, cubic) were observed for BW, BWG, FI, and FCR in both trials and livability in trial 1, as well as for tibia criteria and P retention in trial 2. Livability in trial 2 demonstrated only a cubic response (P = 0.0074) to phytase. Quadratic effects of phytase on ash weight were dependent on xylanase with enzyme interaction being significant (P = 0.0424). Xylanase as a main effect did not significantly impact (P > 0.05) performance in trial 1, nor growth, FI, livability, tibia criteria, or P retention in trial 2. Trial 2 FCR was significantly reduced (P = 0.0345) by xylanase inclusion. Body weight and gain, feed intake, tibia, and retention criteria were greatest and feed conversion lowest at 1,500 FTU/kg, regardless of trial.