A total of 2160 male broilers were distributed over 60 pens to host 5 treatments. A starter feed (day 1 to 21) and finisher feed (day 22-35) were used (both pelleted). A negative control (NC) feed was reformulated by reducing a positive control (PC) feed by 0.2 percentage point protein, 0.02 percentage point dig. Lys (and other essential amino acids keeping a constant ratio to Lys), 0.18 percentage point Ca and P, and 0.09 MJ/kg ME. The PC starter feed contained 202 g/kg crude protein (CP), 11.5 g/kg dig Lys, 12.04 MJ/kg ME broiler, 8.0 g/kg Ca, 6.8 g/kg P, and 4.0 g/kg available P (aP). The PC finisher feed contained 176 g/kg CP, 9.5 g/kg dig. Lys, 12.67 MJ/kg ME broiler, 7.0 g/kg Ca, 5.9 g/kg P and 3.4 g/kg aP. To the NC feeds 0, 250, 500 or 1000 FTU of phytase was added per kg of feed and performance was measured per feeding phase. At 21 days, bone ash was determined on 3 birds per pen. At the end of the trial, 10 birds per pen were killed and ileal samples was collected to determine P, Ca and CP in order to calculate their digestibility.
Results indicated that the phytase at 250 FTU/kg could compensate for the performance loss due to the feeding the NC, bringing body weight back to the PC level (2445 g/b vs 2428 g/b and 2396 g/b for 250 FTU/kg for the PC and the NC, respectively). The final body weight reached 2447 g/b and 2518 g/b for the 500 FTU and 1000 FTU/kg treatments. Feed conversion (FCR) was significantly increased in the NC (1.600 vs 1.572 for the PC; P < 0.05) while the FCR was 1.575 and 1.580 for the 250 FTU/kg and 500 FTU/kg treatment (not significant versus the PC nor NC). The FCR at a dose of 1000 FTU/kg (1.572) was significantly different from the NC (P< 0.05). Bone ash increased in a dose responsive way whereby the 1000 FTU/kg treatment reached nearly the value of the bone ash of the PC (39.2 % vs 39.7 % respectively).
The digestibility of P increased linearly with increasing levels of phytase addition (71.3, 76.9 and 78.4 % for 250, 500 and 1000 FTU/kg versus 46.3 and 48.7 % for the PC and the NC respectively). This effect was significant for all phytase vs PC and NC while the 1000 FTU/kg treatment was also significantly different from the 250 FTU/kg treatment (P < 0.05). Crude protein digestibility increased with phytase addition, however no significant differences between treatments could be detected (73.3, 73.4, 75.5, 76.4 and 76.3 % for PC, NC, 250 FTU/kg, 500 FTU/kg and 1000 FTU/kg, respectively). Ca digestibility was significantly higher for the NC and the phytase supplemented feeds (30.6, 48.2, 49.8, 50.5 and 54.3 %, respectively). Based on the digestibility values and the P, Ca and CP levels in the feed, it was calculated that the phytase at 250, 500 and 1000 FTU/kg resulted in improvements of 1.11, 1.38 and 1.45 g/kg dig P, of 3.95, 5.67 and 5.49 g/kg digestible protein and of 0.11, 0.15 and 0.40 % dig. Ca per kg feed respectively.