title: Ovarian response after gonadotropin treatment of heifers immunized against gonadotropin-releasing hormone.
abstract: Angus x Hereford heifers were used to determine whether the ovaries of heifers immunized against GnRH would respond to exogenous gonadotropins. Heifers (n = 23; 24 mo; 491 +/- 23 kg) were assigned to a 2 x 2 factorial experiment: immunization against GnRH conjugated to human serum albumin (GnRH-IMM) or human serum albumin alone (HSA-IMM), and treatment with gonadotropins (GTH) or saline. The GTH treatment was 2,000 IU PMSG + 1,000 iu hCG, and control heifers were given saline (s.c.). Immunization against GnRH (GnRH-IMM) caused cessation of ovulation (progesterone < 1 ng/mL plasma for 3 wk) and GTH treatment began within 3 to 5 wk after heifers became anovulatory. Heifers immunized against HSA (HSA-IMM) were treated between d 9 and 11 of the estrous cycle. All heifers were given PGF (i.m.) on d 2 (d 0 = start of GTH treatment) and 2,000 IU of hCG (i.m.) on d 4. Ovaries of heifers were evaluated by ultrasound. Blood was sampled daily from d 0 to d 8 and every second day through d 24 to quantify progesterone and estradiol. Concentrations of estradiol increased with time after GTH but the response was reduced by GnRH-IMM (IMM x GTH x day, P < .01). Number of follicles > or = 6 mm (d 0 to 14) was increased after GTH (GTH x day, P < .001) but was decreased (P < .03) by GnRH-IMM. Immunization against GnRH reduced total follicles > or = 6 mm on d 4 in heifers on both saline and GTH treatments. Treatment with gonadotropins increased the number of follicles > or = 16 mm on d 14 compared with control heifers. The number of CL was increased by GTH (GTH x day, P < .001) but the response was reduced (P < .03) in GnRH-IMM heifers compared with HSA-IMM heifers. We conclude that treatment with gonadotropins will induce follicular growth and ovulation in heifers that are anovulatory due to immunization against GnRH.
authors.affiliation: Animal Science Department, Oklahoma Agricultural Experiment Station, Stillwater 74078-0425, USA.
authors.forename: D K
authors.initials: DK
authors.lastname: Bishop
authors.forename: R P
authors.initials: RP
authors.lastname: Wettemann
authors.forename: J V
authors.initials: JV
authors.lastname: Yelich
authors.forename: L J
authors.initials: LJ
authors.lastname: Spicer
mesh_terms: D000818:Animals; D001835:Body Weight / Q000502:physiology; D002417:Cattle / Q000097:blood / Q000276:immunology / Q000502:physiology*; D004958:Estradiol / Q000097:blood; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000276:immunology*; D006062:Gonadotropins / Q000494:pharmacology*; D006801:Humans; D010053:Ovary / Q000000981:diagnostic imaging / Q000187:drug effects / Q000502:physiology*; D010060:Ovulation / Q000502:physiology; D011374:Progesterone / Q000097:blood; D012709:Serum Albumin / Q000276:immunology; D014463:Ultrasonography; D014611:Vaccination / Q000662:veterinary
chemical_list: D006062:Gonadotropins; D012709:Serum Albumin; D007987:Gonadotropin-Releasing Hormone; D011374:Progesterone; D004958:Estradiol