Diameter of the preovulatory follicle of the mare

The mares ovulate follicles between 40-45 mm in diameter, dependingon breed, size, and nutritional status of the mare as well as breeding season. Thus, we aimed to identify the average diameter of the preovulatory follicle of mares belonging to genetic group "Baixadeiro". Three mares raised at the Unit for Research and Conservation of Baixadeiro Horse, located in the Farm School Sao Bento were used - MA (UEMA). They were evaluated for body condition score (BCS) and monitored daily by rectal palpation and ultrasonography using the equipment VET CHISON 600®.When a follicle of 35 mm was identified, its diameters were evaluated daily until ovulation. The mean BCS found was 4.0, which, according to Henneke (Equine Veterinary Journal, v.15, p.371-372, 1983) indicates moderate thinness and may influence reproductive activity according to this author. Gastal et al. (Biology of Reproduction, v.62, p.222, 2000) claim that mares with low BCS ovulate smaller follicules compared with mares in better body condition. Nevertheless, mares showed the following individual mean diameter of the preovulatory follicle: 38.12 ± 2.44; 40.23 ± 3.93; 41.10 ± 4.96. The overall mean was 39.88 ± 3.98, which corresponds to the expected values for the species. According to Murdoch et al. (Biology of Reproduction, v.35, p.1187-94, 1986) preovulatory follicle can reach a diameter of ± 40 mm; Blanchard (Manual of equine reproduction Missouri: Mosby 1998) claims that this value can reach between 40 - 45 mm; Ginther et al. (Theriogenology, v.69, p.583-590, 2008) found that the pre-ovulatory follicle has a diameter of 41 mm reaching a plateau before ovulation. It can be concluded that the mare's genetic group "Baixadeiro" showed mean values of follicular diameter in the range expected for the equine species.