Eight patient cows as the experimental group and 8 multiparous healthy cows in the same dairy-farm as the control were chosen to explore the pathogenesis of ulceration of the sole. Patient cow's pus from the ulcer region and healthy cow's solar contaminations from the junction of sole and bulb were collected to make bacterial separating cultivation and biochemical identification . Blood and ruminal fluid of the two groups were collected to determine the endotoxin concentration with limulus test and the histamine with fluorospectrophotometry respectively. Two groups' sole horn were chipped to measured the sulfur-containing amino acid content with ion exchange chromatography, mineral element Ca,Mg,Zn,Cu,Fe content with atomic absorption spectrophotometry, and Se content with 2,3-diaminonaphthalene fluorescence method respectively. The results were as follows:Staphylococcus aureus, streptococcus pyogenes and Escherichia colibacillus were detected from both the patient group and the control group, no specific pathogenic bacteria being found from the test group. This result prove that solar ulceration is a pododermatitis aseptica circumscripta, and the ulcer region suppuration is due to secondary infection. Compared with the control group, the test group's endotoxin concentrations of blood and ruminal fluid were increased by 0.54 EU/ml(p<0.01) and 0.6 EU/ml(p<0.01) respectively; histamine contents of blood and ruminal fluid were raised by 18.7 ng/ml(p<0.01) and 18.4 ng/ml(p<0.01) respectively; cystine and methionine of sole horn were decreased by 8.7%(p<0.01) and 5.9%(p<0.01) respectively; Zn,Se,Cu concentrations of sole horn were decreased by 21.28μg/g(p<0.01),0.19μg/g(p<0.01) and 1.1 μg/g(p<0.05) respectively. The difference of Ca,Mg,Fe contents of sole horn were no significant between the test group and the control group(p>0.05). These results suggest that the important factors induced solar ulceration of dairy cow are the increase of endotoxin and histamine of blood and ruminal fluid, and the decline of sulfur-containing amino acid and mineral element Zn,Se,Cu of the sole horn.To examine the effects of yeast culture(YC) on plasma endotoxin concentration(PEC) and additional indexes, twelve early lactating (DIM<40d) Holstein cows were randomly allotted to 2 groups based on calving number, days in milk and milk production. Cows were fed a basal diet and treatments were control and control plus Yikang-XP (500g/cow per d from d 1 to 7 , and 120g/cow per d after 7d) with six cows per group. Experimental periods were 60d. Blood samples were collected 1d before feeding XP, 20d, 40d, 60d after adding XP. Limulus test was used to detect plasma endotoxin concentration. Mean daily milk yield, milk fat, milk protein and somatic cell counts were measured periodically. Non-return rate and morbidity were registered simultaneously. The results indicated: compared with the control group, the mean PEC of test group was decreased by 0.925 EU/ml (p<0.01), 1.137 EU/ml (P<0.01) and 0.913 EU/ml(P<0.01) respectively on days 20, 40, and 60 after feeding XP; Milk production was increased by 2.9kg (P<0.05) and 3.61kg(P<0.05) on 20d and 60drespectively; Milk fat percentage, milk protein percentage and Somatic cell counts were not statistically different between treatments (p>0.05 Non-return rate was increased significantly (P<0.01), and morbidity rate was lower in cows fed XP than in cows receiving control diet (p<0.01).Patient cows were randomly grouped and treated by ether iodoform, iodine-tar ointment, zinc sulfate and yeast culture Yikang-XP respectively. The results showed that those cases treated by application only ether iodoform or iodine-tar ointment are usually a longer recovery period and a lower cure rate, while those cases treated by application ether iodoform or iodine-tar ointment plus oral administration zinc sulfate are generally a faster recovery period and a higher cure rate. However, the best therapy measure is iodine-tar ointment plus oral administration zinc sulfate and yeast culture Yikang-XP, because this therapy not on