Resumo

URIBE-VELASQUEZ, Luis Fernando; CORREA-OROZCO, Adriana  e  OSORIO, José Henry. CHARACTERISTICS OF OVARIAN FOLLICLE DEVELOPMENT DURING ESTROUS CYCLE IN SHEEP. Biosalud [online]. 2009, vol.8, n.1, pp.117-131. ISSN 1657-9550.

In most domestic animals, the later stages of follicle development appear to have a wave-like pattern during the estrous cycle. A follicle wave is characterized by the synchronous growth of a cohort of follicles, one (or a species-specific number) which continues growing (dominant follicle), while the others regress due to development inhibition (subordinate follicles). Follicular function has been widely studied in sheep, although the description of the follicular development pattern has been controversial in early studies. Some authors described follicular growth as continuous and independent of the cycle stage. Other studies were supportive of a wave-like pattern. Currently, there is a general agreement that reconciles both viewpoints, which is based on the high variability in the number of cohorts developing in each wave (the cohort of follicles) and the high variability in the number of cohorts developing in each estrous cycle. In this way, follicles > 5 mm in diameter would exhibit a wave-like pattern, whilst follicles smaller than 4 mm would grow randomly. Most studies describe two to four follicle waves during the estrous cycle, with one study describing up to six waves per cycle. Follicular selection is the process that results in a decrease in the number of growing follicles in a wave according to the species-specific number of follicles that ovulate. During the estrous cycle, the dominant and largest subordinate follicles reach maximum diameters of 5-7 and 3-5 mm, respectively. In many cases the ovulatory follicles develop from a cohort of follicles from the last follicular wave. However, the ovulatory follicles can also derive from the second-to-last follicular wave. Understanding the pattern of follicle development in small ruminants is increasingly important for designing improved methods to manipulate reproduction and production.

Palavras-chave : corpus luteum; follicles; ultrasonography; follicular wave.

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