Ram-induced growth of ovarian follicles and gonadotrophin inhibition in anoestrous ewes.
Southdown ewes in mid-seasonal anoestrus were exposed to rams for 0 h (control group), 2 h, 24 h, 40 h, 3 days, 10 days or 20 days. Serial blood samples were then taken to determine LH and FSH levels. Ewes with greater than 24 h ram exposure were ovariectomized immediately after bleeding, and all follicles greater than 1 mm diameter were dissected from the ovaries and measured. LH basal concentrations and pulse frequency increased significantly within 2 h of ram introduction, but by 24 h fell, and then remained low. FSH concentrations fell within 2 h of ram introduction and remained low. Control group ewes (isolated) had no follicles greater than 4 mm diameter, whereas all ewes exposed to rams had large follicles, with CL or preovulatory follicles present at 40 h after ram introduction. Ram introduction was also associated with follicle recruitment (antrum formation to less than 2 mm). Follicular recruitment and development to the large follicle stage therefore occurred during a period of low plasma gonadotrophin levels and suppressed LH pulsing.
D000780:Anestrus; D000818:Animals; D002369:Castration; D004971:Estrus; D005260:Female; D005640:Follicle Stimulating Hormone / Q000097:blood*; D007986:Luteinizing Hormone / Q000097:blood*; D006080:Ovarian Follicle / Q000502:physiology*; D011247:Pregnancy; D012621:Seasons; D012636:Secretory Rate; D012726:Sexual Behavior, Animal; D012756:Sheep; D013997:Time Factors
D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone