Abstract: This experiment was conducted to study the effects of adding Ipriflavone to low-calcium diet on microstructure and histomorphometry of bone in hyline brown laying hens. Two hundred 24-week-old hyline brown laying hens were randomly divided into four groups and fed on diets as follows: control group (containing calcium 3.55% in basic diet), low calcium group (containing calcium 1.27% in low-calcium diet), test groupⅠ(adding 8 mg·kg^－1 Ipriflavone to low-calcium diet) and test groupⅡ(adding 20 mg·kg^－1 Ipriflavone to low-calcium diet) for 60 days. At the end of experiment, 10 hens in each group were killed. Then, demineralized bone sections of the left middle tibias were made for observing the changes of bone microstructure by using OLYMPUS BX41 metalloscope, and some static parameters of bone histomorphometry were measured by Image-Pro Plus 6.0. Tibia microstructure was observed. Compared with control group, cortical bone of low calcium group had many resorption cavities, there were a large number of osteoclasts in the resorption cavities, and osteoclasts increased in the surface of medullary bone trabeculas, the effect of bone resorption was more than that of bone formation and led to osteoporosis. Cortical bone of test groupⅠ had many resorption cavities, there were more osteoclasts in the resorption cavities and the surface of medullary bone trabeculas, the effect of bone resorption was not inhibited. There were a large number of osteogenic cells and osteoblasts in the outer surface of cortical bone in test groupⅡ, the effect of bone formation was increased. And, Static parameters of bone histomorphometry were measured. Compared with low calcium group, Tb.Ar and %Tb.Ar in test group Ⅰ and Ⅱ were very significantly increased (P<0.01). Tb.Pm and Tb.N were higher in test group Ⅰ and Ⅱ than in low calcium group, but the differences were not significant (P>0.05). In test group Ⅱ Tb.Sp was significantly decreased (P<0.05) and Tb.Th was significantly increased (P<0.05). The results showed that adding 20 mg·kg^－1 Ipriflavone to low-calcium diet strengthened bone reconstruction, improved bone metabolism and relieved the occurrence of osteoporosis.

Key words: cage layer osteoporosis, Ipriflavone, low calcium, bone microstructure, bone histomorphometry