Follicle selection in domestic ruminants

摘要: Ultrasound imaging has shown that cattle exhibit 2 or 3 waves of follicular development during an oestrous cycle. The consist the contemporaneous appearance, about every 7 days, a group follicles > = 5 mm in diameter. One follicle gradually becomes larger than rest (i.e. dominant). There are several lines evidence suggesting occur regularly under conditions basal LH and FSH. (1) Cycles with longer have luteal phases do cycles waves, indicating number cycle is determined by time regression. (2) 4 can when phase artificially prolonged exogenous progesterone. (3) Waves pregnancy. However, secondary surge FSH may be important initiating new recruitment after ovulation, since suppression delays first wave development. Follicles functionally dominant (capable ovulating regression) while they still growing early their plateau growth. Functional dominance lost some between late phases, morphologically largest follicle). factors lead to one mechanisms suppress growth subordinate not well understood. When extended low doses progesterone, normal pattern altered ovulatory grows for period time. This finding indicates subtle changes hormonal milieu dramatically alter dynamics experimental model useful studying dominance. In contrast, patterns sheep must assessed more indirect ways, but offer advantage breeds differ ovulation rate. Correlation endocrine environment rate this species provides valuable approach understanding controlling selection It been suggested high achieved increased recruitment, whereas others there selection. oestradiol involved regulating sheep. Follicular requires presence gonadotrophins, particularly general, regulate domestic ruminants Further experiments determine relative roles paracrine ovarian-pituitary-hypothalamic interactions regulation