Effects Of Thermostable Phytase On Plasma Parameters, Bone Quality And Nutrients Utilization Of Laying Duck

A study was conducted to determine the effects of thermostable phytase on plasma parameters, bone quality and nutrients utilization of laying ducks. 200-d-old laying Jinding ducks (750 total ducks) were allotted randomly to 5 treatments with 3 replicates. Diets included a control diet containing adequate level of available phosphorus (AP: 0.45% ) and four diets that were deficient in AP (0.38%, 0.32%, 0.25% and 0.18% respectively) but supplemented with phytase at the level of 500 FTU/kg. At 300 d of age, 6 ducks from each group were selected at random and blood samples (5 ml per duck) were obtained for subsequent determination of plasma parameters. 6 ducks from each group were selected too and killed by cervical dislocation. The left tibiae were removed from the ducks and analyzed for bone characteristics and mineral contents. For determination of mineral retention at 250 d of age, 6 ducks from each group were selected at random to assign to metabolic cages equipping with water troughs and were housed in the cages. Feces and urine from the birds were collected to determine the dietary nutrient utilization.Effects of thermostable phytase on plasma parameters were as follows. Diets AP decreased from 0.45% to 0.25% and supplements with 500 FTU phytase couldn't influence performance, plasma ALP actity, Ca, Mg, Cu and Fe contents (P >0.05). The plasma uric acid content was significantly decreased and plasma Zn content was significantly increased (P <0.05). This might reflect the ducks didn't mobilize the bone phosphorus. The utilization of crude protein and Zn were improved (P <0.05) and that of Cu and Fe were not influced. But the plasma P content of 0.25% AP and 0.32% AP diets supplemented with the phytase were significantly lower than that of 0.45% AP diet (P <0.05). Plasma ALP actity and P content of laying ducks fed 0.18% AP diet with phytase supplementation demonstrated AP level in diet had great variations (P <0.05). The results reflects the duck would mobilize the bone phosphorus in order to maintain normal P homeostasis.Effects of thermostable phytase on bone quality were as follows. Supplementation of the phytase to diets decreased AP levels from 0.45% to 0.25% couldn't influce the tibia wet weight, fat-free weight, length, width at midshaft, density and tibia ash, Ca, P and Cu concentration. This might reflect the tibia was narmal. But the breaking strength of 0.25% AP and 0.32% AP diets supplemented with the phytase were significantly lower than that of 0.45% AP diet (P <0.05). The tibia wet weight, fat-free weight, length, width at midshaft, density and tibia ash, Ca, P, Cu and Zn concentration of 0.18% AP diet with phytase supplementation was significantly lower than 0.45% AP diet (P <0.05). This reflected tibia characteristics of laying ducks fed 0.18% AP diet were decreased even though phytase supplementation.Effects of thermostable phytase on nutrients utilization were as follows. Utilization of crude protein, P and Fe were significantly improved (P <0.05) with diets AP decreased from 0.45% to 0.25% and supplements with 500 FTU phytase. The rate of excretion P was decreased by 4.86%~19.24%. This reflected 0.25% AP levels in diets supplementated with 500 FTU phytase could improve normal homeostasis of crude protein, P and Fe and be profit to environmental protection and ecology. Although 0.18% AP diet with phytase supplementation could normal homeostasis of crude protein, P and Fe (P <0.05), utilization of energy, dry material, Ca, Mg and Zn were not influced (P >0.05).These results demonstrated that supplementation of the phytase to low AP diets could be profit to mineral deposition in tibia and maintain narmal characteristics. The utilization of crude protein was increased and normal P homeostasis was improved. Significant reduction of P excretion could be also achieved. This would be profit to environmental protection and ecology.