Diagnosis and Treatment of the Problem Mare

FOLLICLES THAT FAIL TO OVULATE
Palpation and ultrasonographic examination of follicles in order to try and predict ovulation is an important skill to acquire. Various parameters, some well-established and some the subject of current study are used to help anticipate the time of ovulation. Follicle diameter is a useful tool whilst the follicle retains its spherical shape. Once the follicle has reached a size of around 40 mm (typical Thoroughbred) the follicle is usually soft and loses its spherical shape. In these situations, diameter measurement is less useful. Normal ovulation may be rapid or prolonged with eventual complete or almost complete evacuation of the follicle. Ovulation failure occurs in almost 10% of estrous cycles according to a study by McCue and Squires (2002). These authors report that the majority of anovulatory follicles luteinize (85.7%) but some remain as persistent follicular structures (14.3%). All types of anovulatory follicles are infertile since follicular collapse and oocyte release (ovulation) has not occurred. It is difficult to predict if a dominant follicle will fail to ovulate (McCue 2007). […]