The effect of an extended artificial photoperiod and gonadotrophin-releasing hormone infusions in inducing fertile oestrus in anoestrous mares.
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.
Lowis
T C
TC
Department of Veterinary Clinic and Hospital, University of Melbourne, Werribee, Victoria.
Hyland
J H
JH
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
D007987:Gonadotropin-Releasing Hormone