| The a series of experiments were conducted to assess the stability of liquid phytases,the degradability of phytate P by various phytases and the effectof adding different levels of phytase in the diet containing high and low phytate P on the performance and nutrient digestion or utilization for Cherry Valley ducks.Experiment 1:Four liquid phytases were selected to study their stability at different pH and temperatures.The phytase activity,the relative activity under a range of pH and 3 temperatures(20℃,35℃and 50℃) were analysed.The results showed that the activities of four liquid phytase(1,7,8,9) were 5750U/mL, 1147U/mL,5615U/Ml and 4277U/ml,respectively.The optimum pH of these four liquid phytases was 4.5 where they had the highest relative activity After stored for 4 and 10 weeks at 20℃,the remained phytase activities were 74.78%,44.07%, 60.90%,70.19%and 22.37%,38.68%,29.71%,22.84%for phytase 1,7,8 and 9, respectively.After stored for 4 and 10 weeks at 35℃,the remained phytase activity were 38.44%,38.68%,55.45%,51.60%and 24.91%,11.19%,28.08%,14.61%for phytase 1,7,8 and 9,respectively.However,when the storage temperature increased to 50℃,after 10-week storage,the retained activities of phytases were less than 25% for these phytase products.Experiment 2:This study was designed to assess the degradation of phytate P in wheat and rice bran by the four liquid phytases tested in previous experiment (numbered 1,7,8,9).At pH 5.5,and temperature 37℃,the phytase was incubated with wheat bran or rice bran forⅩⅩhours and the phosphorus content in the supernant was measured every certain time.The results showed that phytases used in this experiment can released a significant amount of phosphorus.The phytase 1 released more P from substrate with high phytate level(e.g.rice bran).It seems that P from wheat bran could be released more rapidly than from rice ran.Based on this trial and the outcomes of previous experiment,phytase 1 was selected for the further assessment using ducks.Experiment 3:The objective of this experiment was to assess the effect of various levels of phytase on the performance,nutrient digestion and utilization by Cherry Valley ducks.A total of 1280 day-old Cherry Valley Ducks were randomly divided into 10 treatments with 8 replicates each treatment and 16 ducks per replicate. There were two types of experimental diets containing high and low phytate(0.33% vs 0.20%).For each types of experimental diet,there were five treatments including a negative control group,a positive control group and three treatment groups in which phytase was added at 250U/kg,500U/kg or 750U/kg respectively to the negative control.The negative control diet contained a lower phosphorus(reduced by 0.138%) and Ca(reduced by 0.12%) than the positive control.The results showed that adding phytase to the two diets significantly improved the growth performance of ducks.Phytic acid did not affect the apparent digestibility of nitrogen and energy.Experiment 4:A total of 600 day-old Cherry Valley Ducks were randomly divided into 10 treatments with 6 replicates each treatment and 10 ducks per replicate. The experimental design is the same as experiment 3 with the objective being to assess the effects of various levels of phytase on the performance and nutrient digestion by 0 to 18-day-old Cherry Valley ducks.There were two types of diets containing high(0.37%) and low(0.25%) levels of phytate phosphorus.The results showed that adding phytase to the two types of dietsary improved increased body weight gain by 18.5%～44.4%and 38.9%～55.6%,declined improved FCR by 2.8% and 26.9%～29.6%.The digestibility of P was increased by 48.0%and 18.1% respectively when phytase was added to the high and low phytate diets at 750U/kg. |
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