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.
