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It's all in the timing: ovulation induction in the mare
  1. Madeleine Campbell, BVetMed, MA, PhD
  1. DipECAR, MRCVS, RCVS and European Specialist in Veterinary Reproduction (Equine), Hobgoblins Stud and Equine Reproduction Centre, Duddleswell, Ashdown Forest, East Sussex TN22 3BH, |UK
  1. e-mail reprovet_uk{at}

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PREDICTION of ovulation is difficult in the mare compared with other species, because of the mare's uniquely protracted luteinising hormone (LH) surge (Alexander and Irvine 2011). In modern horse breeding, the accurate prediction of ovulation is a prerequisite of efficient management systems, be they natural cover or artificial insemination (AI). Ideally, each mare would be covered or inseminated once a year to achieve pregnancy. Minimising the number of coverings/inseminations not only reduces the pressure on heavily booked stallions or the supply of semen, but also minimises the insult to the uterus that breeding inevitably entails (Kotilainen and others 1994), and thus reduces the chances of breeding-induced endometritis (Troedsson 2006) and increases the pregnancy rate.

For these reasons, pharmacological induction or ‘programming’ of ovulation has been routinely adopted in broodmare practice. By using an ovulation induction agent, one can narrow the window of time within which ovulation is likely to occur, and thus optimise pregnancy rates by arranging covering or insemination for the most appropriate time in relation to ovulation, according to the management system or type of semen being used. In the UK, two ovulation induction agents for mares are currently licensed and in common use: human chorionic gonadotrophin (hCG) (Chorulon; MSD Animal Health), and a deslorelin acetate implant (Ovuplant; Dechra Veterinary Products). (Buserelin acetate [Receptal; MSD Animal Health] is also licensed for ovulation induction in mares but is much less commonly used in practice, due to its short-lasting effect and the potential need to …

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