title: Follicular activity and ovulation regulated by exogenous progestagen and PMSG in anestrous ewes.
abstract: Follicular dynamics and ovulation were compared in 3 groups of anestrous ewes: those treated with medroxyprogesterone acetate (MAP) sponges for 12 d, then with 750 IU PMSG at the time of sponge removal (P4 + PMSG, n = 6), or PMSG alone (n = 6) and untreated controls (n = 6). Waves of follicular activity were observed in all the animals. In the P4 + PMSG treatment group, MAP priming permitted more ovulatory follicles (P < 0.001) to be recruited without changing follicle growth rate; MAP priming also delayed the time of ovulation (P < 0.001) and the time of the LH surge (P < 0.01), which allowed for an increase in the size of ovulatory follicles (P < 0.05). Ovulation also resulted in normal luteal function after P4 + PMSG (P < 0.01) but not after PMSG alone, since premature luteal regression occurred in 80% of the cases and was related to the presence of follicles > 4 mm when P4 levels were < 1 ng/mL on the day following ovulation. The results showed that MAP priming increased the ovulation rate by increasing the number of follicles that responded to PMSG.
authors.affiliation: Department of Animal and Poultry Science, University of Guelph, Ontario, Canada.
authors.forename: V
authors.initials: V
authors.lastname: Leyva
authors.forename: B C
authors.initials: BC
authors.lastname: Buckrell
authors.forename: J S
authors.initials: JS
authors.lastname: Walton
mesh_terms: D000818:Animals; D003338:Corpus Luteum / Q000033:anatomy & histology; D005260:Female; D006064:Gonadotropins, Equine / Q000494:pharmacology*; D007986:Luteinizing Hormone / Q000097:blood; D003341:Luteolysis; D017258:Medroxyprogesterone Acetate / Q000494:pharmacology*; D006080:Ovarian Follicle / Q000033:anatomy & histology / Q000187:drug effects* / Q000502:physiology*; D010060:Ovulation / Q000187:drug effects*; D045167:Progesterone Congeners / Q000494:pharmacology*; D012756:Sheep / Q000502:physiology*
chemical_list: D006064:Gonadotropins, Equine; D045167:Progesterone Congeners; D007986:Luteinizing Hormone; D017258:Medroxyprogesterone Acetate