The effects of various concentrations of phytase on broiler growth performance, phosphorus digestibility, tibia ash, and phosphorus utilization
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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.
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