Mareish is a colloquial term used by horse people to describe behaviour in mares that is attributed to hormonal fluctuations — typically associated with oestrus (the period of sexual receptivity in the reproductive cycle). A mareish mare may become irritable, hypersensitive, distracted, reluctant to work, or difficult to handle at certain points in her cycle. It is one of the most frequently discussed topics in equine management, and also one of the most misunderstood.
What Does Mareish Behaviour Look Like?
Mareish behaviour can manifest in a wide range of ways. Some mares become tensely sensitive to leg aids, bucking or swishing their tails when asked to move forward. Others become herd-bound, calling out to other horses, particularly stallions or geldings. Distraction, squealing, frequent urination (winking), and an unwillingness to concentrate on work are also common observations. In severe cases, mares may become difficult to tack up, showing resentment of girthing or back contact.
It is worth noting that not all difficult behaviour in mares is hormonal. Back pain, saddle fit issues, ulcers, and other physical discomforts are frequently misattributed to “being mareish” when a thorough veterinary assessment would reveal an underlying physical cause. See also: gastric ulcers.
The Equine Reproductive Cycle
Mares are seasonally polyoestrous — they cycle during the longer daylight months, typically from spring through autumn in the northern hemisphere. Each cycle lasts approximately 21 days, with oestrus (heat) lasting 4–7 days. During oestrus, rising oestrogen levels produce the classic mareish behaviours. Some mares transition smoothly through their cycles with minimal behavioural change; others are significantly affected.
During winter (the anovulatory period), many mares stop cycling altogether and may actually be calmer and more focused. This leads some owners to notice a marked seasonal improvement in their mare’s behaviour from late autumn through to spring.
Management and Veterinary Options
For mares whose hormonal behaviour genuinely interferes with work or safety, several management approaches exist. Progesterone-based treatments (such as Regumate) can suppress oestrus cycles and are widely used in competition mares, though they require careful handling due to risks to humans. Marbles (glass balls placed in the uterus) are sometimes used as a low-intervention method to mimic pregnancy and suppress cycling, though the evidence for their effectiveness is mixed.
Spaying (ovariectomy) is a more permanent surgical solution available for mares with severe hormonal behaviour, though it is relatively uncommon in the UK. The British Equine Veterinary Association (BEVA) provides guidance on reproductive health in mares: www.beva.org.uk
Frequently Asked Questions
Are all mares mareish?
No. Many mares cycle through their seasons with minimal behavioural change and are just as consistent and willing in their work as geldings or stallions. Mareish behaviour is notably variable — some mares are significantly affected for several days each cycle, others barely at all. Breed, individual temperament, workload, and management all influence how much a mare’s cycle affects her behaviour.
Should I treat my mare’s mareish behaviour with hormones?
This is a veterinary decision and should involve a proper assessment first. Before reaching for hormonal treatments, rule out physical causes — ulcers, musculoskeletal issues, ill-fitting tack, and dental problems can all produce similar symptoms. If a physical cause is excluded and the behaviour is genuinely linked to the reproductive cycle, your vet can discuss the most appropriate management options for your mare’s workload and competitive schedule.
Do mares get worse with age?
Some mares do seem to become more reactive to their cycles as they age, particularly if they have had foals and their cycle becomes more established. However, this is not universal. Regular, consistent work, good management, and appropriate veterinary support can help maintain quality of life and performance for cycling mares well into their competitive careers.