The effect of environmental factors is becoming more significant in animal reproduction under the tropics. This thesis presents a study of the relationship between the circannual reproductive pattern of tropical female equines and environmental factors believed to influence reproduction such as climate, nutritional status and management. The thesis contains 7 chapters including introduction, literature reviews, materials and methods, results, discussion, and conclusions and recommendations. Reproductive activities of jennies and mares (as measured by follicular activities, manifestation of oestrus and incidence of ovulation) were studied using serial ultrasonography, observational study and progesterone assay through three distinctly different seasons. Data were collected on nutritional status, management systems and climate to establish relationships with reproductive pattern. Results are presented in detail in tabulations, figures, and graphics. The findings are discussed and summarized with conclusive remarks. Recommendations on future study prospects are also given.