Breeding your mare and Artificial Insemination (AI) options

These information sheets are provided for your interest. They should not replace veterinary advice from your veterinary surgeon.

Whilst every effort is taken to ensure the accuracy and completeness of the information provided, your specific circumstances must be discussed before advice can be given.

Mon, 11/04/2022 - 10:29 -- Heidi John MRCVS

Artificial insemination


  • Much wider choice of stallion including abroad
  • Less risk of introducing infection in the mare
  • Improved pregnancy rates with some problem mares
  • Reducing travelling for mare and foal


  • Closer monitoring of the mare’s cycle
  • Extra costs for vet work, hormones and transport
  • Not accepted by the TB breeding industry
  • Fee for AI covers a cycle or a fixed dose of semen and does not guarantee a pregnancy
  • Some stallion semen is not suitable for chilling or freezing
  • Frozen semen is associated with slightly lower pregnancy rates



Fresh: The mare and stallion are resident at the same premises and the semen is transferred to the mare shortly after collection.

Chilled: Semen is collected from the stallion; an extender is added, and it is chilled and couriered to the mare for insemination with 24hrs. For UK based mares only suitable from the UK or parts of mainland Europe.

Frozen: can be obtained from stallions standing anywhere in the world. The semen is concentrated and preserved in straws, virtually indefinitely and stored in liquid nitrogen. A dose or doses are shipped to the insemination centre or vet practice prior to the mare being lined up for insemination.


Natural service



  • Cost effective and good pregnancy rates
  • Stud fees are often on a ‘no foal free return’ basis


  • Mares with young foals need to travel to the stud to be covered
  • Not offered by all stallions due to injury risk
  • Increased risk of injury to stallion, mare handlers



The pregnancy rates for natural service and fresh or chilled semen in young healthy mares are around 60%. Frozen semen pregnancy rates are slightly less at 40-50%.



Most mares are suitable for AI with chilled semen, but frozen semen is not generally advised for mares over 15 years of age, those being bred to foal heat or of reduced fertility due to the lower conception rates.

Once a stallion is selected, check whether chilled or frozen is available – and whether the semen has proven pregnancies with the preferred option – due to the different way’s semen handles being processed. We as your vets can guide you through these options and this is often discussed at a pre-breeding assessment visit.


Chilled AI can easily be carried out at your own premises – sedation maybe required for the mare. Frozen AI can be carried out at home – but in some circumstances going into a clinic is less time consuming for owner and vet as more scans are needed with this option. With natural covering the mare will usually travel to the stallion for a ‘walk in’ covering at the optimum time of the cycle decided by a vet scanning her – or stay at the stud and get covered by the stallion while she is ‘in season’.

Travelling to a stud involves blood samples and swabs being taken from the mare to prevent the spread of disease to the stallion and other mares.