Effects of steam conditioning temperatures on commercial phytases and subsequent broiler performance and tibia mineralization

Objective: Phytase enzymes support broiler phosphorus requirements and vary in thermal stability and manufacturer suggested protocols for determining activity. Our objective was to evaluate nutrient degradation, determined using phytase markers, broiler performance, and tibia mineralization from diets based on corn and soybean meal subjected to increasing steam conditioning temperatures. Materials and Methods: Three commercial phytase products (B Trich, E Pichia, E Trich) were analyzed for activity at 2 laboratories. The lower obtained activity was used to include each product at 1,000 phytase units/kg of the diet. Each product was applied to a negative control (NC) diet before steam conditioning at 82, 88, or 93°C, pelleting, and crumbling. A 4 × 3 factorial arrangement in a randomized complete block design created 12 treatments fed to 8 replicate cages of 10 Hubbard × Cobb straight-run broilers for 20 d. Results and Discussion: Phytase product effects demonstrated that NC-fed broilers had the lowest feed intake and live weight gain, whereas broilers fed E Trich had the greatest feed intake and live weight gain (P < 0.05). Broilers fed B Trich and E Pichia had lower feed conversion ratio compared with NC-fed broilers, and broilers fed E Trich were intermediate (P < 0.05). Increased conditioning temperature sequentially decreased feed intake and live weight gain (P < 0.05). Main effects interacted such that tibia ash measures decreased as conditioning temperature increased; however, mineralization differences were less dramatic in NC-fed birds. Implications and Applications: Increased conditioning temperature may have decreased nutrient availability per se and denatured phytase products, or both factors may have contributed to performance detriment.