The effects of various concentrations of phytase on broiler growth performance, phosphorus digestibility, tibia ash, and phosphorus utilization
Two experiments were conducted to determine the effects of various phytase concentrations on broiler growth performance, carcass composition, phosphorus digestibility, tibia ash and phosphorus utilization. The first experiment contained a positive control (PC) diet that was sufficient in all nutrients, a diet reduced in available phosphorus, calcium, amino acids and energy utilized as a negative control (NC) diet and the NC diet supplemented with two different phytase products at three inclusions (500, 1000, and 2000 FTU/kg) all fed to broilers over a 42-day period. The NC fed birds resulted in reduced growth performance by 42 days of age and phytase at 500 and 1000 FTU/kg had increased growth performance compared to NC (P<0.01), resulting in a similar response to the PC fed birds (P>0.05) indicating phosphorus and other nutrient release from the NC diet with phytase supplementation. Birds fed a diet supplemented with phytase A at 2000 FTU/kg outperformed the PC fed birds in body weight gain, feed efficiency, cold carcass weight, breast weight, breast yield, breast + tender weight and yield (P<0.01), but 2000 FTU/kg of phytase B resulted in poor responses often not improved in comparison to the NC fed birds (P>0.05). The second experiment utilized a standard curve to evaluate the use of phytase at various concentrations over a 14 day feeding assay. There were no differences between the two phytase treatments (500 and 2000 FTU/kg) in body weight gain, feed efficiency, feed intake or tibia ash weight (P>0.05). Standard curve analysis of tibia ash weight resulted in an estimate of 0.15 phytate phosphorus release from both phytase treatments. At 14 days, birds fed a treatment supplemented with phytase at 2000 FTU/kg showed an increase in apparent ileal phosphorus digestibility in comparison to 500 FTU/kg fed birds. The data may suggest that birds are digesting more phosphorus at an inclusion of 2000 FTU/kg phytase than 500 FTU/kg phytase but are not able to effectively utilize or store the nutrient as tibia ash showed similar mineral deposition between the two treatments. The concentration of non-phytate (nPP) in the Experiment 2 was 0.20% nPP (0.30% nPP in Experiment 1), which might have precluded the growth performance effects noted in Experiment 1. These two experiments indicate that phytase can act as a viable method in supplementing phosphorus and has the potential to increase broiler growth performance but results may vary depending on the phosphorus deficiency status of the diets before phytase supplementation.