title: Follicular, hormonal, and pregnancy responses of early postpartum suckled beef cows to GnRH, norgestomet, and prostaglandin F2alpha.
abstract: Cycling (n = 16) and noncycling (n = 24), early postpartum, suckled beef cows of three breeds were assigned randomly to three treatments: 1) 100-microg injection of GnRH plus a 6-mg implant of norgestomet administered on d -7 before 25 mg of PGF2alpha and implant removal on d 0 (GnRH+NORG); 2) 100 microg of GnRH given on d -7 followed by 25 mg of PGF2alpha on d 0 (GnRH); or 3) 2 mL of saline plus a 6-mg implant of norgestomet administered on d -7 followed by 25 mg of PGF2, and implant removal on d 0 (NORG). All cows were given 100 microg of GnRH on d +2 (48 h after PGF2alpha). Blood sera collected daily from d -7 to d +4 were analyzed for progesterone and estradiol-17beta, and ovaries were monitored daily by transrectal ultrasonography to assess changes in ovarian structures. Luteal structures were induced in 75% of noncycling cows in both treatments after GnRH, resulting in elevated (P < .01) progesterone on d 0 for GnRH+NORG-treated cows. Concentrations of estradiol-17beta (P < .01) and LH (P < .05) were greater on d +2 after GnRH for cows previously receiving norgestomet implants. Pregnancy rates after one fixed-time AI at 16 h after GnRH (d +2) were greater (P < .05) in GnRH+NORG (71%) than in GnRH (31%) and NORG (15%) cows. Difference in pregnancy rate was due partly to normal luteal activity after AI in over 87% of GnRH+NORG cows and no incidence of short luteal phases. The GnRH+NORG treatment initially induced ovulation or turnover of the largest follicle, induction of a new follicular wave, followed later by increased concentrations of estradiol-17beta and progesterone. After PGF2alpha, greater GnRH-induced release of LH occurred in GnRH+NORG cows before ovulation, and pregnancy rates were greater after a fixed-time AI.
authors.affiliation: Department of Animal Sciences and Industry, Kansas State University, Manhattan 66506-0201, USA.
authors.forename: K E
authors.initials: KE
authors.lastname: Thompson
authors.forename: J S
authors.initials: JS
authors.lastname: Stevenson
authors.forename: G C
authors.initials: GC
authors.lastname: Lamb
authors.forename: D M
authors.initials: DM
authors.lastname: Grieger
authors.forename: C A
authors.initials: CA
authors.lastname: Löest
mesh_terms: D000818:Animals; D000833:Animals, Suckling; D001947:Breeding / Q000379:methods*; D002417:Cattle / Q000502:physiology*; D003338:Corpus Luteum / Q000187:drug effects / Q000502:physiology; D015237:Dinoprost / Q000494:pharmacology*; D004971:Estrus / Q000187:drug effects; D004973:Estrus Synchronization; D005260:Female; D005298:Fertility / Q000187:drug effects; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology*; D006080:Ovarian Follicle / Q000187:drug effects / Q000502:physiology*; D049590:Postpartum Period; D011247:Pregnancy; D011282:Pregnenediones / Q000494:pharmacology*; D045167:Progesterone Congeners / Q000494:pharmacology*
chemical_list: D011282:Pregnenediones; D045167:Progesterone Congeners; D007987:Gonadotropin-Releasing Hormone; C100284:norgestomet; D015237:Dinoprost