| ABSTRACT one hundred and twenty 19-wk-old ISA hens were randomly allocated to one of three dietary levels of total phosphorus: 0.58, 0.44, 0.30 (AP: 0.4, 0.25, 0.10 respectively). Birds were fed the diets for 21 weeks during which blood samples were collected every 2 weeks to analyze for blood calcium, blood phosphorus, alkaline phosphatase (AKP), osteocalcin (BGP), calcitonion (CT), estrogen (E2), tibia bone mineral density (BMD) and eggshell quality were also determined. About every I month 5 hens of three levels dietary phosphorus were killed and tibia were collected for histopathological research. Egg production, body weight and eggshell quality were significantly decreased in hens of TP: 0.30 compai-ied to the other two group(PKO.U1). There were no significant vwiety among different dietary phosphorus groups in blood calcium, phosphorus. Osteocalcin. alkaline phosphatase of hens of TP:3.0 were significantly decreased as compared to the control hens. E2 had a tendency to increase, but there is no difference among three dietary phosphorus hens. The research based on histopathological and histoniophometry research revealed that hens?cnacellous and medullary bone were normal at onset of the test, only a few number of osteoblasts were found. Many rssorption cavities in cancellous bone and many osteoblastsin these cavities as welas on the surface of trabulaewere found in two groups of phosphorus deficiencies in period of middle and late test. It was more severe in group of TP: 0.30 than group of TP: 0.44. As the test went on ,the number of resorption cavity, osteoblasts and volume of the cavity increascd. At the same time. there appeared small and some resorption cavity and many osteoblasts in control group finally. In conclusion, The deficient dietary phosphorus (TP: 0.44) which may be in the range of ~marginal phosphorus?obtained a good production and eggshell quality of hens, but induced to bone damage.
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