Follicular mapping by ovarian ultrasound and the timing of ovulation in the Friesian mare - case raport

Abstract

In equines, the reproductive activity is seasonal polyserial, thus starting with the spring months and until the autumn there are cyclic estrous manifestations. The months of May, June and July are characterized by a much more pronounced manifestation and expression of estrus. The duration of the sexual cycle can vary from 9 to 33 days, estrus, on the other hand, has a variation from 2 to 10 days, even more. Ovulation takes place 24-48 hours before the end of heat. The oocyte is released in metaphase II, the moment when the oocyte can be fertilized. In the Friesian horse breed, the expression and intensity of estrus is very variable, a fact that leads to difficulty in anticipating the moment of mating or artificial insemination (AI). Currently, the most widespread method of anticipation of ovulation is the monitoring of follicular development, through which changes in the size, structure and shape of the ovulatory follicle are observed. By using repeated ovarian ultrasound, a map of the ovarian follicles was drawn up and the follicles were followed in the dynamics of evolution as a follicular wave, until the ovulatory type follicle and the appearance of the corpus luteum (CL). With the first probable signs of proestrus, follicle sizing began at T0: left ovary F=1.9 cm, right ovary F=2; F = 3.9; F=1.8 cm, at T1 (+4 days) left ovary: F=2; F=2 cm, right ovary: F=2, F=1,9, F=4.2/4.4 cm, at T2 (+16 h) left ovary F= 2cm and others smaller, right ovary F= 4,5/5.2 cm spherical with thickened wall, at T3 (+12 h) left ovary F=2 cm, right ovary F= 5/5.6 cm conical and cloudy, at T4 (+12 h) left ovary F=ovulate (corpus hemorrhagicum). In this case, the Friesian mare is characterized by the development of several follicles on each ovary, but the follicle ovulates at over 5.5 cm.