title: Use of GnRH agonist implants for long-term suppression of fertility in extensively managed heifers and cows.
abstract: The ability of gonadotrophin releasing hormone (GnRH) agonist implants to suppress ovarian activity and prevent pregnancies, long-term, was examined in heifers and cows maintained under extensive management. At three cattle stations, heifers (2-year-old) and older cows (3- to 16-year-old) were assigned to a control group that received no treatment, or were treated with high-dose (12 mg, Station A) or low-dose (8 mg, Station B and Station C) GnRH agonist implants. The respective numbers of control and GnRH agonist-treated animals (heifers + cows) at each station were: Station A, 20 and 99; Station B, 19 and 89; Station C, 20 and 76. Animals were maintained with 4% bulls and monitored for pregnancy at 2-monthly intervals for approximately 12 months. Pregnancy rates for control heifers and control cows ranged from 60-90% and 80-100%, respectively, depending on the study site. The respective number of animals (heifers + cows) treated with GnRH agonist that conceived, and days to first conception, were: Station A, 9 (9%) and 336 +/- 3 days; Station B, 8 (10%) and 244 +/- 13 days; Station C, 20 (26%) and 231 +/- 3 days. Treatment with high-dose GnRH agonist prevented pregnancies for longer (approximately 300 days) than treatment with low-dose GnRH agonist (approximately 200 days). In the majority of heifers and cows treated with GnRH agonist, ovarian follicular growth was restricted to early antral follicles (2-4mm). The findings indicate that GnRH agonist implants have considerable potential as a practical technology to suppress ovarian activity and control reproduction in female cattle maintained in extensive rangelands environments. The technology also has broader applications in diverse cattle production systems.
authors.affiliation: School of Animal Studies, The University of Queensland, Gatton, Qld 4343, Australia. mdocchio@uqg.uq.edu.au
authors.forename: Michael J
authors.initials: MJ
authors.lastname: D'Occhio
authors.forename: Geoffry
authors.initials: G
authors.lastname: Fordyce
authors.forename: Tim R
authors.initials: TR
authors.lastname: Whyte
authors.forename: Tristan F
authors.initials: TF
authors.lastname: Jubb
authors.forename: Lee A
authors.initials: LA
authors.lastname: Fitzpatrick
authors.forename: Neil J
authors.initials: NJ
authors.lastname: Cooper
authors.forename: William J
authors.initials: WJ
authors.lastname: Aspden
authors.forename: Matt J
authors.initials: MJ
authors.lastname: Bolam
authors.forename: Timothy E
authors.initials: TE
authors.lastname: Trigg
mesh_terms: D000822:Animal Husbandry / Q000379:methods; D000818:Animals; D001315:Australia; D001835:Body Weight; D002417:Cattle / Q000502:physiology*; D003271:Contraceptive Agents, Female / Q000008:administration & dosage / Q000494:pharmacology*; D004343:Drug Implants; D005260:Female; D005298:Fertility / Q000187:drug effects*; D008297:Male; D006080:Ovarian Follicle / Q000187:drug effects; D011247:Pregnancy; D011897:Random Allocation; D012621:Seasons; D017329:Triptorelin Pamoate / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000494:pharmacology*
chemical_list: D003271:Contraceptive Agents, Female; D004343:Drug Implants; D017329:Triptorelin Pamoate; C066438:deslorelin