Optimal phytase supplementation levels for broilers differ by thermal condition for phosphorus utilization but not...

Area of Science:

• Animal Science
• Poultry Nutrition
• Nutritional Biochemistry

Background:

• Dietary calcium (Ca) and phosphorus (P) are critical for broiler development.
• Heat stress (HS) negatively impacts broiler performance and nutrient utilization.
• Phytase supplementation can enhance nutrient availability from plant-based feed ingredients.

Purpose of the Study:

• To evaluate the effects of phytase on broilers under thermoneutral and heat stress (HS) conditions.
• To determine optimal phytase inclusion levels for different environmental conditions.
• To assess phytase's impact on growth, bone mineralization, and nutrient utilization in reduced Ca and P diets.

Main Methods:

• A 2x5 factorial experiment with 420 male broiler chicks was conducted.
• Birds were subjected to thermoneutral or cyclic HS conditions.
• Diets included a positive control, a Ca- and P-deficient negative control (NC), and NC with varying phytase levels (500, 1000, 1500 FTU/kg).
• Growth performance, bone mineralization, and nutrient utilization were measured.

Main Results:

• Phytase supplementation linearly/quadratically improved average daily gain (ADG), average daily feed intake (ADFI), bone mineralization, and Ca and P utilization (P < 0.05).
• Optimal phytase levels for ADG, ADFI, tibia strength, and nitrogen excretion were similar under both temperature conditions (approx. 500-800 FTU/kg).
• Optimal phytase for P utilization was higher under HS (987 FTU/kg) than thermoneutral conditions (536 FTU/kg) (P = 0.029).

Conclusions:

• Phytase effectively improves broiler performance, bone mineralization, and P utilization in reduced Ca and P diets.
• Optimal phytase levels are criterion and environment-dependent.
• Supplementing with optimal phytase can restore performance to positive control levels and enhance P utilization beyond positive control levels, especially under HS.