Effects Of Phytase On Growth Performance And Nutrient Utilization In AA Broilers

This study was aimed to investigate the effect of phytase on the growth performance, nutrient utilization, tibia quality and biochemical parameters in AA broilers, which offered evidence to approach the mechanism and the application of phytase. The research included three experiments.Experiment1:960one-day-old Arbor Acre (AA) chicks were selected to study the effects of different dose and dosage form of phytase on the growth and slaughter performance and the development of digestive organs. The birds were randomly divided into8groups with6replicates of20chickens each (10males and10females). The feeding trial consisted of two periods(starter:0～3weeks of age; grower:4～6weeks of age). The dietary treatments were as follows:positive control (PC, corn-soybean based diet with adequate available phosphorus); negative control (NC, diets with0.1%available phosphorus reduced); the rest six treatments were NC added with coated phytase (500,1000and10000U/kg), powdery phytase (500U/kg), granular phytase (500U/kg) and overseas powdery phytase (500U/kg), respectively. The results showed that:(1) Enzyme treatments had no significant effect on feed intake and ADG except that granular phytase treatment had a higher (P<0.05) feed intake in the grower period compared to PC. Granular phytase improved (P<0.05) feed:gain ratio in the starter period compared to PC and NC, and PC had a lower (P<0.05) feed:gain ratio than NC in the overall period (P>0.05).(2) During six weeks,10000U/kg coated phytase markedly increased semi-eviscerated rate, but powdery phytase not only increased the simi-eviscerated rate but also the eviscerated rate significantly compared to PC(P<0.05). Enzyme treatments had a tendency to reduce the breast muscle rate and leg muscle rate (P>0.05).500U/kg coated phytase decreased abdominal fat rate by34.50%(P<0.01). Both the thickness of subcutaneous fat and the width of chest fat had no marked difference (P>0.05). Almost enzyme treatments except overseas powdery phytase significantly improved (P<0.05) the heart index compared to compared to PC. There were no significant differences of the organ index of liver, spleen, pancreas, thymus and bursa of fabricius among all treatments.Experiment2:The treatments were the same as experiment1to study the effect of different dose and dosage-form of phytase on the nutrient utilization and the digestive enzyme activity in broilers. The results as follows:(1) At28d, powdery phytase significantly increased (P<0.01) the digestibility of DM above PC and the500U/kg coated phytase treatment, and a higher (P<0.05) digestibility of energy above NC and EE compared to500U/kg coated phytase were also observed in the powdery phytase. The digestibility of P was improved (P<0.05) by all phytase treatments except500U/kg coated and overseas powdery phytase. Compared to PC, higher digestibility of arginine was obtained in1000U/kg coated phytase, powdery and granular phytase respectively. Besides,500U/kg coated phytase significantly increased (P<0.05) the digestibility of valine, methionine, serine and cystine, and a higher digestibility of glycine was observed in granular phytase. At42d, granular and overseas phytase markedly improved (P<0.05) the digestibility of DM and P above PC. There was no significant difference of the digestibility of amino acids, CP and P in overall treatments.(2) At28d, all the treatments had a tendency to increase the lipase activity in broilers. The same results of trypsin and disaccardase activity were observed in42-d-old broilers.Experiment3:The treatments were the same as experiment1to study the effect of different phytase addition on the tibia quality and biochemical parameters in broilers. The results indicated that500U/kg coated phytase increased (P<0.05) tibia length above PC and NC at28d. Compared to NC, a higher (P<0.05) phosphorus content of tibia was obtained in10000U/kg coated and granular phytase. Phytase addition had no effect on dry weight, ash and calcium content of tibia. For’42-d-old birds,1000U/kg coated phytase, markedly improved the dry weight of above PC and tibia length compared to NC (P<0.05).10000U/kg coated phytase increased (P<0.05) the calcium content of tibia above PC and NC. The increase (P<0.05) was observed in500U/kg coated phytase above NC. There was no effect on the ash content of tibia in the experimental groups.(2) For28-d-old broilers, a higher (P<0.05) calcium content in plasma was obtained in1000U/kg coated phytase compared to PC. Phytase addition had no effect on the alkaline phosphatase, albumin, total protein and globulin. At42d, the1000U/kg and10000U/kg coated phytase increased (P<0.05) the calcium level in plasma compared to NC. The increase (P<0.05) of total protein was observed in the overseas powdery phytase above PC, and the globulin level of overseas phytase was lower (P<0.05) than powdery phytase treatment. Compared to PC and NC, there were no differences on the activity of alkaline phosphatase, albumin and globulin, and the level of phosphatase in the plasma.In conclusion, the data indicated that supplementation of different dose and dosage-form phytase in low-phosphorus diets improved the growth performance, nutrient utilization, tibia quality and the biochemical parameters in broilers. Seen from every index, the effect of500U/kg coated and granular phytase were the most suitable.