Performance, carcass quality, tibia ash, and mineral digestibility responses of Ross 708 broilers to increasing dose of two commercially available mixer-added phytases

Abstract

Mixer added phytases must maintain efficacy post-conditioning and pelleting. Heat from saturated steam and friction upon pellet die extrusion may deactivate phytases. The objective of this study was to assess the thermostability of 2 commercially available phytases concentrated at 500, 1,000, or 2,000 FTU/kg in mixed mash post-steam conditioning at 82°C for 30 s and extrusion through a 4.8 × 38 mm pellet die and the subsequent effect on 0 to 44-d Ross 708 male broiler performance, mineral digestibility, and tibia ash responses. The phytase sources were both derived from E. coli and expressed in Trichoderma Reesei , (QB) and Pichia pastoris , (OP). A 3 (Phytase level) × 2 (Phytase source) factorial arrangement of treatments within a randomized complete block design was utilized. A positive control and negative control diet based on available phosphorus ( P ) and total calcium ( Ca ) were also manufactured and analyzed within a multiple comparison. Diets were fed to 8 replicate pens of 30 chicks in 3 phases. Live performance, d 20 and d 44 tibia ash, d 44 hot boneless, skinless breast weight, and mineral digestibility were measured. Phytase sources did not differ in their effect on live performance or breast yield. Calcium digestibility was increased for birds fed OP relative to QB ( P < 0.05). Phosphorus digestibility increased as phytase level increased ( P < 0.05). D 20 tibia ash percentage increased for 1,000 and 2,000 FTU/kg for both phytase sources ( P < 0.05). All phytase treatments increased d 44 tibia ash relative to the NC; however, OP tibia ash further increased when supplemented above 500 FTU/kg ( P < 0.05). The assessed phytase sources showed similar benefit to live performance and breast yield but varied in response to tibia ash and mineral digestibility at different concentrations. It is important to note that the conclusions in this study were derived using specific phytase products that were analyzed for activity by using a specific protocol, and diets were pelleted within a selected range of processing conditions (i.e., 82°C and 30 s of conditioning); using alternative methodologies may result in different conclusions.