Equis ISSN 2398-2977

Therapeutics: reproductive system

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

Gonadal function

All reproductive hormones have the potential to interfere with the reproductive systems of humans, and should be handled with particular care and caution, particularly by women of childbearing age. Many of the drugs listed should not be handled by pregnant women. Some have additional safety requirements for humans of both sexes and the data sheets of the individual drugs should be consulted before use.The use of many reproductive hormones is forbidden by the regulatory authorities governing many different equine sports; such rules should always be checked before treatment.Many of the therapeutic uses of drugs for treatment of the reproductive system are unlicensed and as such should only be used under the prescribing cascade and with fully informed owner consent.


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 or IM.
      • Administration: mares need to be in estrus (endometrial edema, relaxed cervix) for >3 days with a dominant follicle of >35 mm. Ovulation can be expected 24-48 h after injection (usually ~36 h post-injection, depending on the size of the follicle at the time of treatment).
      • Side effects: repeated administration of hCG during the same breeding season has been associated with mares becoming refractory to ovulation induction with hCG due to production of antibodies against hCG (which may cross-react with endogenous LH). This effect can be minimized by using the lower end of the suggested dose range.
      • 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 developing, dominant follicle of >30 mm. Ovulation within 48 h (usually ~40-42 h post-injection, depending on size of follicle at the time of treatment).
    • 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 has been used. However, the problem appears to have been associated with the formulation of the implantation tablet in some countries, and implantation into the vulva lips is not necessary with all formulation and is an unlicensed route of use.
  • Buserelin 0.0042 mg/mL (Receptal):
    • Solution for injection.
    • 40 µg (10 mL) IV, IM or SC.
    • The licensed use is to induce ovulation of a mature follicle in mares (via increasing luteinizing hormone).
    • Buserelin also been used 8-12 days post-ovulation to prevent early embryonic death in mares. This is an unlicensed use for which (written) informed owner consent should be given prior to drug administration. For induction of ovulation - 40 µg by IM (or IV or SC) injection once a pre-ovulatory follicle has reached its maximum size and 6 h before breeding, repeated after 24 h if mare has not ovulated.
    • For the unlicensed use of supporting early embryo survival, 40 µg by IM (or IV or SC) injection once, between day 8 and day 12 post-ovulation.

Sex hormones

This article is available in full to registered subscribers

Sign up now to purchase a 30 day trial, or Login

Prostaglandins

This article is available in full to registered subscribers

Sign up now to purchase a 30 day trial, or Login

Ecbolics

This article is available in full to registered subscribers

Sign up now to purchase a 30 day trial, or Login

Dopamine antagonists

This article is available in full to registered subscribers

Sign up now to purchase a 30 day trial, or Login

Others

This article is available in full to registered subscribers

Sign up now to purchase a 30 day trial, or Login

Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Barker K J, Mateu Sánchez S, Serrano Y R, Lacey F M & Crabtree J R (2019) Prostaglandin F2 alpha-induced maternal behaviour for fostering orphan foals and for mares demonstrating foal rejection. Equine Vet J 61, S53.
  • Schramme A et al (2010) Pharmacokinetics of carbetocin, a long-acting oxytocin analogue, following intravenous administration in horses. Equine Vet J 40 (7), 658-661 PubMed.
  • Ginther O J, Beg M A, Gastal E L, Gastal M O & Cooper D A (2009) Treatment with human chorionic gonadotropin (hCG) for ovulation induction is associated with an immediate 17beta-estradiol decrease and a more rapid LH increase in mares.  Anim Reprod Sci 114 (1-3), 311-7 PubMed.
  • Hemberg E, Lundeheim M & Einarsson S (2006) Successful timing of ovulation using Deslorelin (Ovuplant) is labour-saving in mares aimed for single Ai with frozen semen. Reprod Domest Anim 41 (6), 535-7 PubMed.
  • Barker C, Echeverria K & Davis M (2006) Effects of different doses of PGF2 on luteal function and on the subsequent estrous cycle. Anim Reprod Sci 94, 207–209. 
  • Daels P F, McCue P M, DeMoraes M J & Hughes J P (1996) Persistence of the luteal phase following ovulation during Altrenogest treatment in mares. Theriogenology 46 (5) 799-811 PubMed.
  • Fuchs A R (1987) Prostaglandin F2α and oxytocin interaction in ovarian and uterine function. J Steroid Biochem 27, 1073-1080 PubMed.

Other sources of information

  • Bertone J J & Horspool L J I (2004) Eds. Equine Clinical Pharmacology. Saunders, UK. ISBN: 0702024848.
  • The NOAH Compendium of Datasheets of Licensed Veterinary Medicines. Website: https://www.noahcompendium.co.uk/home.


ADDED