Background: Trade horses in Nigeria are not vaccinated against leptospirosis. Clinical biochemistry profile of Leptospira IgG (LEP-IgG) seropositive trade horses, alongside the effect of physiological factors (age, sex and pregnancy) were determined in this study. Methods and materials: Blood samples were collected via jugular veins of 129 horses of varying ages and sex at the Obollo Afor horse lairage. The harvested sera were subjected to qualitative test for LEP-IgG antibodies by sandwich ELISA method, and serum biochemistry evaluation which followed standard procedures. Results: A total number of 16 (12.4%) trade horses were recorded to be Leptospira seropositive. A significant association was recorded between the presence of LEP-IgG antibodies and age (p = 0.025), sex (p = 0.005), and pregnancy (p = 0.009). The mean serum total protein, albumin and total cholesterol values of the Leptospira seropositive trade horses were significantly (p < 0.05) lower than those of seronegative horses. Also, the mean blood urea nitrogen (BUN) level was significantly (p < 0.05) higher than those of seronegative horses. The mean serum ALT, AST, ALP and total protein values of the seropositive stallions were significantly (p < 0.05) lower than those of the Leptospira seropositive mares. The mean serum albumin and creatinine values of the Leptospira seropositive stallions were significantly (p < 0.05) higher than those of the Leptospira seropositive mares. The serum ALP of the seropositive young horses was significantly (p < 0.05) lower than those of the adult and horses. The mean serum albumin of young horses was significantly (p < 0.05) higher than those of old trade horses. The mean serum ALP value of the pregnant mares was significantly (p < 0.05) higher than that of the non-pregnant mares. The mean serum albumin value of seropositive pregnant mares was significantly (p < 0.05) lower than those of the non-pregnant seropositive mares. Also, the serum globulin and creatinine values of seropositive pregnant mares were significantly (p < 0.05) higher than those of the non-pregnant seropositive mares. Conclusion: Therefore, it was concluded that the seroprevalence of leptospirosis in trade horses was 12.4%. LEP-IgG seropositive horses were hypoproteinaemic, hypoalbuminaemic, hypocholesterolemic, with elevated levels of BUN. This suggests that the level of anti-LEP IgG is less protective and leptospirosis in horses is more associated with hepatic than renal involvement.