| Chinese grass turtle(Chinemys reevesii),an omnivorous economic animal,is docile and easy to breed,and has higher edible and medical value with a broad market prospect,its breeding production has gradually increased in recent years.Calcium is an indispensable mineral element in the growth and development of Chinese grass turtle,but there are many kinds of calcium sources with different availability at present,so it is particularly important to choose the right calcium source,determine the calcium to phosphorus ratio and the requirement of calcium,Thus this study focused on above issues.Three common calcium sources candidates were used for in vitro digestion experiments to determine the appropriate calcium source.And with the identified suitable calcium source as the main source of calcium and calcium dihydrogen phosphate as the main source of phosphorus in the dietary,the Chinese grass turtles were cultured for 8 and 12 weeks,respectively,to evaluate the effects of different dietary calcium to phosphorus ratio,calcium and phosphorus content on the growth performance,digestibility,turtle shell nutrient composition,serum biochemistry,and liver and intestinal health.The study contents and results are as follows.1.Research on suitable calcium sourcesThree common calcium sources,calcium carbonate,calcium citrate and calcium lactate,were selected to determine the appropriate calcium source by in vitro digestion.The results showed that calcium lactate was more dialyzable than calcium citrate than calcium carbonate.Therefore,calcium lactate was used as the main calcium source for subsequent experiments.2.Effects of different dietary calcium to phosphorus ratio on growth,digestibility,nutrient composition,serum biochemistry and antioxidant capacity of liver and intestinal in Chinese grass turtles.To investigate the appropriate calcium to phosphorus ratio in Chinese grass turtle diets,five experimental diets of isonitrogenous and isoenergetic(approximately 43.21%crude protein and 5.98% crude lipid)were formulated containing different ratios of calcium to phosphorus of 1:1,1.5:1,2:1,2.5:1 and 3:1,respectively.Twenty pools were divided into five groups,four replicates in each group.The Chinese grass turtles had an initial mean weight of 25.55 ± 2.15 g and were reared for an 8-week The results showed that appropriate calcium and phosphorus ratios in the diets could promote the growth performance of turtles,the shelling rate and specific growth rate(SGR)of turtles fed the diets with calcium to phosphorus ratio of 1.5:1 were significantly higher than that fed the diets with calcium to phosphorus ratio of 1:1,and the SGR and feed efficiency(FE)of turtles fed the diets with calcium to phosphorus ratio of 1.5:1 were significantly higher than that fed the diets of 3:1,the length and height of dorsal carapace and the length and width of plastron of turtles fed the diets of 2:1 were significantly higher than that fed the diets of 1:1(P<0.05).With the increase of dietary calcium to phosphorus ratio,the gastric amylase activity decreased and then increased,the gastric lipase activity exhibited an increasing trend,while the intestinal trypsin activity showed a decreasing trend(P<0.05).The crude ash contents of turtle shell and leg bones of turtles fed the diets of 1.5:1 was significantly higher than those fed the other diets,and the highest crude protein contents of turtle shell was observed at turtles fed the diet with calcium to phosphorus ratio of 1:1(P<0.05).As the dietary calcium to phosphorus ratio increased,the calcium contents of serum and turtle shell rose and then decreased,the magnesium contents of serum and calcium contents of leg bones decreased,and the phosphorus contents of leg bones increased(P<0.05).The total protein contents of serum increased and then decreased with the increase of dietary calcium to phosphorus ratio,the blood ammonia contents was the highest in the turtles fed the diets of calcium to phosphorus ratio of 2:1,and the urea nitrogen contents was the lowest in the turtles fed the diets of 1.5:1(P<0.05).In serum,as the dietary calcium to phosphorus ratio increased,the total antioxidant capacity tended to increase,superoxide dismutase activity decreased and then increased,while alkaline phosphatase activity increased and then decreased,catalase activity in the dietary calcium to phosphorus ratio of 1:1 was significantly higher than those in the dietary of 2:1,and glutathione transaminase activity was the highest in the dietary calcium to phosphorus ratio of 2.5:1(P<0.05).With the dietary increase of calcium to phosphorus ratio,the triglyceride contents in the liver showed a trend of increasing and then decreasing,and was the highest in the dietary calcium to phosphorus ratio of 2:1.Total antioxidant capacity,superoxide dismutase,glutathione transaminase and alkaline phosphatase activities were significantly decreased,the contents of malondialdehyde and glutathioneS-transferase activities increased and then decreased(P<0.05),and catalase activity increased(P<0.05)and then tended to stable(P>0.05).The intestinal total antioxidant capacity was significantly higher in the dietary calcium to phosphorus ratio of 1:1 and 3:1groups than those in the other experimental groups.Superoxide dismutase activity of intestine decreased and then increased with increasing calcium to phosphorus ratio in the diets,catalase activity increased significantly,the content of malondialdehyde was significantly higher in the dietary calcium to phosphorus ratio of 2:1 than those in the dietary of 1.5:1,and alkaline phosphatase activity was significantly higher in the calcium to phosphorus of 3:1 dietary group than those in the other experimental groups(P<0.05).Using SGR,FE and shelling rate as evaluation indicators,the optimum dietary calcium to phosphorus ratio of the Chinese grass turtle was determined to be 1.5:1.3.Effects of different dietary calcium and phosphorus level on growth,digestibility,nutrient composition,serum biochemistry and antioxidant capacity of liver and intestinal in Chinese grass turtles.To determine the appropriate levels of calcium and phosphorus in the diets of Chinese grass turtle,the third experiment was conducted on the basis of determining the optimum calcium to phosphorus ratio in the second experiment.Five experimental diets of isonitrogenous and isoenergetic(approximately 43.88% crude protein)were formulated containing graded levels of calcium at 3000 and 2000,3500 and 2333,4000 and 2667,4500 and 3000,5000 and 3333(mg/kg),respectively.Twenty pools were divided into five groups,four replicates in each group.The initial mean weight of Chinese grass turtles was 62.14 ± 5.33 g and the turtles were reared for a 12-week.The results indicated that the shelling rate of Chinese grass turtles was significantly affected by calcium level and tended to increase with the increase of calcium level,is the lowest at the dietary calcium level of 3000 mg/kg and the highest at 5000 mg/kg(P<0.05).While final body weight(FBW),WGR,survival rate,SGR,FE,feeding rate(FR)and the morphology indexes of turtle shell were not significantly different between groups(P>0.05).As the dietary calcium and phosphorus levels increased,gastrointestinal protease activity tended to decrease,gastric lipase activity increased and intestinal lipase increased and then decreased(P<0.05).The moisture contents of turtle shell decreased with the increase of calcium and phosphorus levels,the crude lipid contents decreased and then increased,the crude protein contents in the dietary calcium level of 3000 mg/kg was significantly higher than the other experimental groups;the crude ash contents of turtle shell and leg bones was the lowest in the dietary calcium level of 3000 mg/kg(P<0.05).With the increase of calcium and phosphorus levels,Serum calcium and phosphorus contents tended to rise,the calcium contents of leg bone were the highest in the dietary calcium level of 4500 mg/kg and the phosphorus contents were the lowest in the dietary calcium level of 5000 mg/kg(P<0.05).Serum albumin contents in the calcium level of 4500 mg/kg were significantly higher than those in the calcium level of 3000mg/kg,3500 mg/kg and 5000 mg/kg.Total cholesterol contents were the highest in the dietary calcium level of 4000 mg/kg,blood ammonia contents tended to increase with increasing calcium and phosphorus levels(P<0.05).The total antioxidant capacity,superoxide dismutase activity and catalase activity of the liver were the highest and the malondialdehyde contents was the lowest in the dietary calcium levels of 3500 mg/kg and4000 mg/kg.Alkaline phosphatase activity in the dietary calcium levels of 5000 mg/kg was significantly lower than those in the other groups.Glutathione transaminase activity increased significantly with increasing calcium and phosphorus levels,and the glutathione-S transferase activity increased and then stabilized with increasing calcium and phosphorus levels(P<0.05).The total antioxidant capacity of the dietary calcium level of 5000 mg/kg was higher than that of the other experimental groups,and alkaline phosphatase activity was the highest in the dietary calcium level of 3500 mg/kg(P<0.05).The optimum calcium and phosphorus level in the diets was determined to be 4000 and2667 mg/kg respectively,taking the shelling rate and the organism health of the Chinese grass turtle as the evaluation index. |
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