| The experiments took Hyline laying hens as test object, on the one hand, we tested the bone growth rules of the back-up Hyline, such as the morphological characteristics,deposition of calcium and phosphorus and the organism metabolism, which would be valuable to establish the evaluation system of the back-up laying hens from the bone health view. On the other hand, we researched the relation between the laying hen bone mobilization and the laying rate, egg shell qualities and the immunological stress, which would reveal the metabolism of laying hen bone calcium and phosphorus homeostasis.The experiment 1 investigated the relationship between the bone growth and the calcium and phosphorus metabolism in laying hens, 500 broilers of 1-day old were feed at the common practice. 8 Hyline pullets were drawn blood and the tibia and femur were collected at 2-week?4-week?6-week?8-week?10-week?12-week?14-week?16-week?18-week?20-week?32-week(95% laying rate)?62-week(80% laying rate) and 77-week old(70% laying rate). The results showed that the bone grew fast before 14-week old, and the bone growth finished at 18-week old. The calcium and phosphorus contents of bone and blood increased obviously at the first laying period, which was similar with the estradiol contents in blood,that showed the layer body maturation and sexual maturation were reached at the same time.The osteocalcin and calcitonin contents both decreased during the experiment, which meant the bone mineralization weakened as the chicken grew. The results of bone metabolism gene test showed that the femur and tibia resorption occurred at different time, the bone resorption came to the top while the laying rate went down to 80%, when the laying rate went down to70%, which may be obsoleted, the bone resorption would weaken and the bone formation would strengthen.The experiment 2 investigated the relationship between the bone calcium and phosphorus mechanism and the laying rate. By artificial selection from 100 laying hens, the laying hens at late period of laying(75-week old) were divided into three groups-- the high laying rate group(100%), the low laying rate group(41%) and the stop laying group. For each group, themetabolism experiment of calcium and phosphorus was conducted to test the differences among these groups,and 8 laying hens were drawn blood and the tibia and femur were collected. The results showed that although the bone morphology index had no differences,the tibia strength and femur strength strengthened obviously as the laying rate decreased, and the calcium content of blood decreased as well. As for the bone metabolism gene expression test, the tibia and femur gene expressed differently, which meant the tibia and femur had different abilities while the layers bone metabolism was interrupted, and the femur was stronger than the tibia. As for the metabolism experiment of calcium and phosphorus,different laying rate layers took different content of calcium and phosphorus every day, but the output content of calcium and phosphorus was similar, which meant the calcium and phosphorus requirements of egg laying could satisfy by autophage.The experiment 3 investigated the relationship between the bone calcium and phosphorus mechanism and the eggshell qualities. On the one hand, 100 layers of late laying period(65-week old) were observed for 2 weeks, the different sites of broken eggs and the correlation analysis were conducted between the egg shell thickness and the egg shell strength.On the other hand, we divided the laying hens into two groups according to their laying egg shell quality while the laying rate(78%) and the age(65-week old) between them was same,each group had 8 layers. The metabolism experiment of calcium and phosphorus was conducted, and the blood and the tibia and femur were collected. The results showed that the egg shell was more likely to break in the two terminals, and the blunt end broken eggs accounted for nearly half amounts of broken eggs, and the eggshell thickness of two terminals were thinner than the middle part. The bone strength of different eggshell layers had no differences,but the bone calcium and phosphorus contents of layers laying broken eggs were lower than the normal laying hens obviously, and the tibia and femur bone absorption gene expression of layers laying broken eggs increased than the normal laying hens, which meant the production of broken egg might be connected with the deficiency of calcium.The experiments 4 investigated the influences of immunological stress to the bone calcium and phosphorus mechanism. 20 laying hens of same age(65-week old) were divided into the LPS group and the control group, the LPS group hens were treated with intraperitoneal injection by 0.15mg/kg BW/d while the control group hens were injected withsaline by the same dose. The injection was conducted for 10 days, and the metabolism experiment of calcium and phosphorus was conducted to test the differences between two groups. The results showed that the LPS injection could change the food intake at first, and the qualities of eggs can be influenced. But as the injection went by time, the influences of LPS to laying hens could weaken gradually. The LPS injection could decrease the calcium and phosphorus level in serum, but had no effect on egg shell quality and the metabolism of calcium and phosphorus.In conclusion, the back-up hens bone grew fast at the first 14 weeks, and the bone growth finished at 18-week old, the deposition of calcium and phosphorus in bone increased obviously at the age of egg-laying maturity, and the gene related to bone metabolism had no changes at all during the brood time. During the egg laying period, the mobilization of tibia and femur happened at different time, but it came to the top at the 80% laying rate. At the late laying period, the changes of egg shell quality might decreased the bone qualities, but the laying rate and the immunological stress had no influences to the bone qualities. |
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