Abstract: [Objective] To assess the effect of thiram on femoral growth and development in broiler chickens, and to evaluate the protective efficacy of Morinda officinalis polysaccharide （MOP） against the femoral injuries induced by thiram. [Method]A total of 300 one-day-old AA broiler chickens were randomly divided into control group, thiram model group, and low-, moderate-, high-dosage MOP treatment groups. There were 3 replicates for each group and 20 broiler chickens for each replicate. The control group was fed with a basal diet; from 4^th to 7^th days of the experiment, thiram model group and three MOP treatment groups were fed with basal diets added with 50 mg/kg thiram; during the whole experiment, 250, 500 and 1 000 mg/L MOP were supplied for low-, moderate- and high-dosage MOP treatment groups in drinking water. The experiment lasted for 15 days. The clinical manifestations of the broiler chickens in each group were observed; on 7^th, 11^th and 15^th days of the experiment, the femur and blood samples were collected; the morphological observation of femur was carried out, the shearing force, physical indexes （weight, length, volume and density）, dry matter contents, calcium and phosphorus contents, ash contents_（DM）, ash contents_（FM）, and ash densities of the femur samples were determined, and the plasma contents of calcium and inorganic phosphorus were tested. The inter-group differences of the experimental data were statistically analyzed. [Result]The broiler chickens in thiram model group appeared claudication, the serious ones were unable to stand, and had shorter femur compared with those in control group. On 7^th day of the experiment, the femur shearing force of thiram model group was significantly （P<0.05） decreased compared with control group. During the whole experiment, the 4 physical indexes of thiram model group were significantly （P<0.05） lower than those of control group; the femur weights of low-dosage MOP treatment group were significantly （P<0.05） higher than those of thiram model group on 11^th day of the experiment, and the femur lengths of low- and moderate-dosage MOP treatment groups were significantly （P<0.05） higher than those of thiram model group on 15^th day of the experiment. The calcium contents in femur of thiram model group were significantly （P<0.05） lower than those of control group on 7^th day of the experiment, and the dry matter contents, ash contents_（FM）, and ash densities in femur of thiram model group were significantly （P<0.05） lower than those of control group on 11^th day of the experiment; the dry matter contents in femur of high-dosage MOP treatment group were significantly （P<0.05） higher than those of thiram model group on 11^th day of the experiment. The plasma contents of inorganic phosphorus of moderate-dosage MOP treatment group were significantly （P<0.05） higher than those of control group on 15^th day of the experiment.[Conclusion]Thiram inhibits the femoral growth and development in broiler chickens via decreasing the strength, physical indexes and calcium deposition of femur, and MOP can protect and alleviate the femoral injuries induced by thiram.

Key words: thiram, Morinda officinalis polysaccharide, broiler chickens, femur, calcium and phosphorus contents, ash contents