Research On Feeding Effects Of Coated Phytaseadditive On Broilers Fed Low Phosphorous Pelleted Diet

This research through study on methods of evaluating thermostability of coated phytase, screened out a more scientific laboratory method that can reflect the effect of practical tempering and pelleting condition on coated phytase activity. In feeding trial, through decrease the phosphorus level in corn-soybean meal, and added different dosage of coated phytase, discussed the effects of different levels of thermostable coated phytase on broilers'dietary available phosphorous'replacement level, growth performance, nutrient digestibility, tibia quality and blood biochemical index.Experiment 1:This study take thermostable coated phytase as test material, through the systematic comparison of water-bath processing, dry heat processing and moist heat processing on the evaluation results of coated phytase's thermostability, and through comparing the correlation between the testing results of the three methods and the testing results under the practical tempering and pelleting condition, in order to screen out a more scientific laboratory method that can reflect the effect of practical tempering and pelleting condition on coated phytase activity. The results showed that: the phytase activity loss ratio presented linear increasing along with the rising of temperature. The correlation analysis results between the testing results of the three laboratory methods and the testing result under the practical pelleting condition showed that: the result of moist heat processing had the strongest correlativity with the result under the practical pelleting condition. In conclusion, the method of moist heat processing is the relative ideal laboratory method to evaluate the effect of practical tempering and pelleting condition on coated phytase activity effectively.Experiment 2:This experiment used the cross classification design with 2 experimental factors and 3 levels, had 9 treatments and 1 control group. The 2 experimental factors was the different available phosphorous content and the different phytase supplemental level respectively. The control group was the basical diet contained normal phosphorous level, and without phytase supplementation. The 3 available phosphorous levels were as follows: 0.45%/0.40%, 0.35%/0.30%, 0.25%/0.20%, and the 3 phytase supplemental levels were as follows: 50g/t,100g/t,150g/t,they formed 9 combination. Seven hundred and twenty 1-day-old Arbor Acre(AA) chicks were randomly allocated to 10 treatments with 6 replicates of 12 chicks each replicate, half male and half female. The feeding trial lasted for 42 days, involved the earlier stage(0-21d) and the later stage(22-42d). The experiment was aimed at testing the effects of coated phytase on growth performance and nutrient utilization in broilers. The results showed that: in earlier stage, the phytase supplementation could not improve growth performance of broilers significantly fed low phosphorous (P>0.05). In later stage, the feed transformation efficiency had significant increase in the 3 treatments with different available phosphorous content and in the 2 treatments of 100g/t, 150g/t phytase supplemental levels (P<0.01), and the feed transformation efficiency rised along with the increasing of phytase supplementation. In whole stage, the feed transformation efficiency of the treatment contained 0.35% available phosphorous had extremely significant rise in comparison with the control (P<0.01). The ADG of the treatments of 100g/t, 150g/t phytase supplemental levels had the rising tendency in comparison with the control (P>0.05), and their feed transformation efficiency had extremely significant rise in comparison with the control (P<0.01). The ADG in the whole stage had the rising tendency along with the increasing of phytase supplementation (P>0.05). Synthesized each growth performance index, the results indicated that: it could not satisfy broilers'nutrient requirement in the diet contained 0.25% available phosphorous content with 50g/t phytase supplementation. In the diet contained 0.25% available phosphorous content with 150g/t phytase supplementation could improve the growth performance in later stage and whole stage (P<0.05). In the diet contained 0.35% available phosphorous content with100g/t ,150g/t phytase supplementation could improve feed transformation efficiency significantly in later stage and whole stage (P<0.05). The combination of 0.35% available phosphorous content with 100g/t phytase supplementation was the optimal combination, it meaned that adding 100g/t phytase in broilers'corn-soybean meal could replace 35% CaHPO4, and could replace 1.0g available phosphorous per kilogram diet. The results of all nutrient utilization indexs showed that: the utilization of crude protein, crude fat, ash and phosphorous in 0.30% low phosphorous treatment had the rising tendency in comparison with the control (P>0.05), the utilization in 0.20% low phosphorous treatment with phytase supplementation had non significant improvement (P>0.05). The utilization of crude protein, crude fat, ash and phosphorous in 0.30% low phosphorous content combined with 150g/t phytase supplementation had improving tendency (P>0.05).Experiment 3:This experiment was conducted on the basis of feeding trial, chose 1 chick from each replicate randomly at the 8:00 am in 43d of the feeding trial, and extracted blood form each chick's vein, and then collected the serum in order to testing the content of calcium, phosphorous and the activity of ALP in serum. Then extracted the left tibia to testing the content of ash, calcium and phosphorous in tibia. The results showed that: the contents of tibia ash, calcium and phosphorous in treatments contained different available phosphorous contents had the rising tendency in comparison with the control (P>0.05). The 100g/t phytase supplementation was the optimal level to the benefit of the tibia's growth, and it could not continue improve the tibia's growth when the supplemental level rised to 150g/t. The testing results of blood biochemical indexs indicated that: it could remit the condition of phosphorous lack when added phytase in low phosphorous diet. The content of serum calcium in each treatment had non significant difference (P>0.05). The content of serum phosphorous had the rising tendency with 100g/t and 150g/t phytase supplementation (P>0.05). The content of serum phosphorous had the indirect rising tendency in 0.30% available phosphorous content with phytase supplementation (P>0.05). The phosphorous metabolization could not improve in 0.20% available phosphorous content with phytase supplementation (P>0.05), and the broilers still lack in phosphorous under this condition.