| The aim of this study was to observe the effects of dietary calcium and phosphorus deficiency on body weight,rickets incidence,bone development and the calcium and phosphorus metabolism in serum and bone of broilers from 1 to 42 days of age,so as to reveal the correlations of the above indicators and find the key indicators of rickets induced by calcium and phosphorus deficiency of broilers.The experiment was carried out by a 2×2 two-factor completely randomized trial design.A total of 504 one-day old Arbor Acres（AA）commercial broilers were divided into 1 of 4 treatments with 7 replicates cage of 12 broilers per cage according to their body weight.According to the dietary calcium and non-phytate phosphorus requirments for broilers from 1-21 and 22-42 days of age recommended by NRC（1994）,there were 4 kinds of diets including 2 calcium levels（1.00 and 0.35%for 0-3weeks;0.90 and 0.30%for 4-6 weeks）and 2 non-phytate phosphorus levels（0.45 and0.23%for 0-3 weeks;0.35 and 0.18%for 4-6 weeks）.The experiment lasted for 42days.The results showed as the following:（1）Compared with the normal calcium and phosphorus group,the phosphorus deficiency,calcium deficiency and the calcium-phosphorus deficiency significantly reduced（P<0.0001）the body weight of broilers on d 14,21 and 28,and the phosphorus deficiency group had the lowest（P<0.0001）body weight of broilers in each days of age and higest（P<0.05）rickets incidence in each phase.（2）Compared with the normal calcium and phosphorus group,the phosphorus deficiency significantly increased（P<0.006）serum calcium contents on d 7,14,21,and 28,but decreased（P<0.05）serum phosphorus contents on d 7,21,and 28 and the serum 25-（OH）2-VitD3 content on d 7 and 14.The calcium deficiency group and calcium-phosphorus deficiency group had lower（P<0.05）serum calcium contents on d 7,21 and 28,and had higher（P<0.05）serum phosphorus contents on d 7 and 28 and the serum 25-（OH）2-VitD3 content on d 7 than the phosphorus deficiency group.（3）Compared with the normal calcium and phosphorus group,the phosphorus deficiency,calcium deficiency and calcium-phosphorus deficiency significantly increased the tibia alkaline phosphatase activity on d 14 and decreased（P<0.0001）tibia ash content,tibia breaking strength,and bone mineral density.The phosphorus deficiency group had the higher（P<0.0003）alkaline phosphatase activity and lower（P<0.0001）tibia ash content,tibia bone strength,and bone mineral density than the calcium deficiency and the calcium-phosphorus deficiency groups.（4）The incidence of rickets was positively correlated with serum calcium contents（r=0.536,P<0.0001）and the alkaline phosphatase activity in serum（r=0.45,P<0.0001）and tibia（r=0.474,P<0.0001）,but negatively correlated with the contents of serum phosphorus（r=-0.440,P<0.0001）,25-（OH）2-VitD3（r=-0.248,P<0.005）,tibia ash（r=-0.762,P<0.0001）,ash phosphorus（r=-0.417,P<0.0001）,bone breaking strength（r=-0.423,P<0.0001）and bone mineral density（r=-0.455,P<0.0001）.In summary,the body weight,incidence of rickets,contents of serum phosphorus and calcium,25-（OH）2-VitD3 content,tibia ash content,alkaline phosphatase activity,bone breaking strength and bone mineral density of broilers were the most sensitive to phosphorus deficiency,followed by calcium deficiency and calcium-phosphorus deficiency.Therefore,the contents of serum phosphorus and calcium,25-（OH）2-VitD3 content,tibia ash content,the alkaline phosphatase activity,bone breaking strength and bone mineral density could be used as key indicators of rickets induced by calcium and phosphorus deficiency in broilers. |
