EN
The paper focuses on analyzing the reasons for abnormalities in follicular, ovulation and luteal function. Disturbances of these kinds are most often diagnosed in winter and transitional periods, and in old and lactating mares. These abnormalities affect ovulation cycles and cause sub fertility. Disturbances of follicular development, ovulations and luteal function can be diagnosed by anamnesis, estimation of sexual behavior, rectal palpation and ultrasonograph, and serum hormonal analysis. In order to give an accurate estimation and prognosis of follicular development and ovulation examinations of follicular vascularization (color-Doppler USG) and follicular fluid analysis (concentrations of: 17-β estradiol, inhibin-B, androstenedion, progesterone, heparin-like anticoagulant) must be performed. An accurate diagnosis of follicular abnormalities, ovulation and luteal function is necessary in order to choose the most suitable treatment.