title: Effect of length of progesterone exposure during ovulatory wave development on pregnancy rate.
abstract: The objective was to determine the effects of the duration of progesterone exposure during the ovulatory wave on fertility (pregnancy rate) in beef cattle. We tested the hypothesis that short-progesterone exposure during the growing and early-static phase of the ovulatory follicle (analogous to the ovulatory wave of 3-wave cycles) is associated with higher fertility than a longer duration of exposure (analogous to the ovulatory wave of 2-wave cycles). Three to 5 days after ovulation, beef heifers (n = 172) and suckled beef cows (n = 193) were given an intravaginal progesterone-releasing device (CIDR) and 2.5 mg estradiol - 17β +50 mg progesterone im to induce a new follicular wave. Cattle were allocated to short- or long-progesterone exposure groups (for 3 and 6 d after wave emergence, respectively) after which prostaglandin F(2α) was administered and CIDR were removed. Forty-eight hours later, all cattle were given 12.5 mg pLH and artificially inseminated (AI) with frozen-thawed semen. The diameter of the two largest follicles and the corpus luteum were measured by transrectal ultrasonography at CIDR removal, insemination, and 36 h after insemination. Pregnancy diagnosis was done ultrasonically 38 and 65 d post-AI. There was no difference in pregnancy rates in short- vs long-progesterone exposure in heifers (53 vs 47%, P = 0.44) or cows (63 vs 58%, P = 0.51). However, the diameter of the ovulatory follicle at CIDR removal and AI was smaller in short- than in long-progesterone groups (P < 0.02), and larger in cows than in heifers (P < 0.006). In conclusion, short-progesterone exposure during the growing and early-static phase of the ovulatory follicle (similar to 3-wave cycles) was not associated with higher fertility than a longer progesterone exposure (similar to 2-wave cycles).
authors.affiliation: Department of Veterinary Biomedical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.
authors.forename: F C F
authors.initials: FC
authors.lastname: Dias
authors.forename: R J
authors.initials: RJ
authors.lastname: Mapletoft
authors.forename: J P
authors.initials: JP
authors.lastname: Kastelic
authors.forename: G P
authors.initials: GP
authors.lastname: Adams
authors.forename: M G
authors.initials: MG
authors.lastname: Colazo
authors.forename: B C
authors.initials: BC
authors.lastname: Stover
authors.forename: O
authors.initials: O
authors.lastname: Dochi
authors.forename: J
authors.initials: J
authors.lastname: Singh
mesh_terms: D000282:Administration, Intravaginal; D000818:Animals; D002417:Cattle / Q000502:physiology*; D015237:Dinoprost / Q000008:administration & dosage; D004958:Estradiol / Q000008:administration & dosage; D005260:Female; D005298:Fertility / Q000187:drug effects*; D007315:Insemination, Artificial / Q000662:veterinary; D006080:Ovarian Follicle / Q000000981:diagnostic imaging / Q000187:drug effects / Q000502:physiology*; D010060:Ovulation / Q000187:drug effects / Q000502:physiology*; D011247:Pregnancy; D011374:Progesterone / Q000008:administration & dosage*; D013997:Time Factors; D014463:Ultrasonography
chemical_list: D011374:Progesterone; D004958:Estradiol; D015237:Dinoprost