title: Seasonal variation in oestrus, the secretion of oestrogen and progesterone and LH levels before ovulation in the ewe.
abstract: Ewes with cervical ovarian autotransplants were studied after PGF-2alpha-induced luteal regression in November and February (mid- and late-breeding season) and June (anoestrum). Progesteron and oestradiol-17beta secretion rates and LH concentrations were determined in serial ovarian venous blood samples and the ewes were frequently tested for oestrus. All 4 ewes in November and 3 of the 4 ewes in February exhibited oestrus and endocrine changes indicative of ovulation. The remaining ewe in February and the three ewes in June failed to show elevated oestradiol-17beta secretion rates after luteal regression, indicating the absence of follicles in the final stages of maturation. The preovulatory rise in the oestradiol-17beta secretion rate, the LH surge and the display of oestrus all occurred earlier, with respect to the PGF-2alpha infusion, in November than in February, suggesting a greater stimulation of folliculogenesis, and therefore a greater availability of maturing follicles, in November than in February.
mesh_terms: D000818:Animals; D004958:Estradiol / Q000378:metabolism*; D004971:Estrus; D005260:Female; D007986:Luteinizing Hormone / Q000378:metabolism*; D010060:Ovulation; D011247:Pregnancy; D011374:Progesterone / Q000378:metabolism*; D012621:Seasons; D012756:Sheep / Q000502:physiology*
chemical_list: D011374:Progesterone; D004958:Estradiol; D007986:Luteinizing Hormone