title: The effect of an extended artificial photoperiod and gonadotrophin-releasing hormone infusions in inducing fertile oestrus in anoestrous mares.
abstract: The occurrence of fertile oestrus early in the breeding season is of paramount importance to the Thoroughbred industry to facilitate early conception. This paper compares 2 techniques for inducing fertile oestrus in anoestrous mares using either an extended photoperiod alone or together with gonadotrophin-releasing hormone (GnRH) infusions. Eleven mares were placed under conditions of 16 h light and 8 h darkness and 5 of these were implanted with osmotic minipumps delivering approximately 100 ng GnRH/kg/h for 28 days (treated mares). The treated mares ovulated 27.7 days earlier than and conceived 32 days earlier than the 6 mares not given GnRH. GnRH-induced ovulations were followed by a competent luteal phase. The combination of GnRH pumps implanted 2 weeks before commencement of service together with extended photoperiod from July 1 has promise in assisting the stud breeder to improve reproductive efficiency on commercial stud farms.
authors.affiliation: Department of Veterinary Clinic and Hospital, University of Melbourne, Werribee, Victoria.
authors.forename: T C
authors.initials: TC
authors.lastname: Lowis
authors.forename: J H
authors.initials: JH
authors.lastname: Hyland
mesh_terms: D000818:Animals; D004971:Estrus / Q000187:drug effects* / Q000528:radiation effects; D005260:Female; D005306:Fertilization / Q000187:drug effects / Q000528:radiation effects; D007987:Gonadotropin-Releasing Hormone / Q000008:administration & dosage / Q000494:pharmacology*; D006736:Horses / Q000502:physiology*; D015918:Infusion Pumps, Implantable / Q000662:veterinary; D008027:Light; D010060:Ovulation / Q000187:drug effects* / Q000528:radiation effects; D010507:Periodicity
chemical_list: D007987:Gonadotropin-Releasing Hormone