Equis ISSN 2398-2977

Therapeutics: reproductive system

Contributor(s): Graham Munroe, Simon Staempfli, Vetstream Ltd

Gonadal function

Human chorionic gonadotropin (hCG)

Action

  • Females: induction of ovulation.
  • Males: stimulation of testicular testosterone production.

Use

Preparations

  • Human chorionic gonadotrophin (Chorulon): commercially available as freeze-dried preparation of 1500 IU.
  • Use:
    • Induce predictable timing of ovulation:
      • Dose: 1500-3000 IU IV.
      • Administration: mares need to be in season (endometrial edema, relaxed cervix) for >3 days with a dominant follicle of >35 mm. Ovulation can be expected 24-48 h after injection (~36 h post-injection).
      • Side effects: repeated administration of hCG during the same breeding season has been associated with mares becoming refractory to ovulation induction with hCG.
      • Higher doses of hCG (4500-6000 IU) have been associated with lower conception rates.
    • Detection of cryptorchidism:
      • Dose: 10,000 iu IV.
      • Blood sampling for testosterone: baseline prior to injection, and then 1 h and 24 h post-injection.

The following preparations are also not licensed for use in the horse in the UK.

Gonadotropin releasing hormones (GnRH analogues)

Action

  • GnRH stimulates secretion of luteinizing hormone (LH) and follicle stimulating hormone (FSH) from the anterior pituitary gland.

Use

Preparations

  • Deslorelin 2.1 mg (Ovuplant):
    • Administration: SC implant. Mares need to be in season (endometrial edema, relaxed cervix) for more than 3 days with a dominant follicle of >32 mm. Ovulation within 36-48 h (~40-42 h post-injection).
    • Side effects: transient injection site reaction with mild swelling can occur. In a small number of mares a prolonged inter-estrus interval with reduced follicular activity and in very rare cases a complete shutdown of ovarian activity has been observed. In order to prevent this happening, implantation of Ovuplant into the vulvar lips with subsequent implant removal after ovulation is recommended.
  • Buserelin 0.0042 mg/mL (Receptal):
    • Solution for injection.
    • 10 mL IV, IM or SC.
    • Not commonly used for ovulation induction in UK.
    • Veterinary literature reports similar ovulation rates compared to Chorulon or Ovuplant within 48 h, if given to mares in season for more than 3 days with a dominant follicle of >35 mm.
    • Administration of 10 ml of Buserelin 8-12 days post-ovulation improved pregnancy rates in two studies by 10%. The mechanism of action remains unclear.

Sex hormones

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Prostaglandins

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Ecbolics

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Dopamine antagonists

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Others

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Further Reading

Publications

Refereed papers

Other sources of information

  • Bertone J J & Horspool L J I (2004) Eds. Equine Clinical Pharmacology. Saunders, London. ISBN: 0702024848.
  • Derived from The Veterinary Formula (2004) 6th edn. Ed: Bishop Y. British Veterinary Association and Royal Pharmaceutical Society. ISBN: 0853695792.


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