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Why does my mare behave badly?

A world-first vaccine developed in Australia provides a new way to manage difficult mares and fillies.

Does your mare change from being an easy-to-handle angel into a cranky, temperamental and unmanageable witch over spring and summer? Does her behaviour get worse when she’s in season, or at other times in her breeding cycle?

Temperament and behaviour problems in mares and fillies related to the breeding cycle - also known as the oestrous cycle - are a common source of complaint from owners, riders, trainers and everyone else involved with handling horses.

A new treatment for this problem has recently become available. Your veterinarian can now prescribe a vaccine for managing behaviour in mares and fillies associated with the breeding cycle.

Common signs of ‘marey’ behaviour

The commonly observed behaviour problems associated with the breeding cycle in mares and fillies may include some or all of the following:

  • Tail raising, frequent urination, wet tail and hind end
  • Squatting down, dropping hips, adopting breeding posture
  • Vulval ‘winking’ or ‘showing’
  • Squealing, aggression, kicking, ears back
  • Increased interest in nearby stallions and geldings
  • Difficulty in handling or riding
  • Decreased co-operation or concentration during riding or training
  • Nervousness and anxiety
  • Unpredictable behaviour

These types of undesirable behaviour do not only affect the rider or trainer of the mare; they can also influence the behaviour and concentration of other horses nearby. This can be a particular problem at horse shows, events, equestrian centres, pony clubs, riding schools, training stables and racetracks. It may only take one cycling mare to create a major scene!

Why does my mare behave in this way?

The breeding cycle of most mares is regulated by day-length, with nutrition and climate also playing their part. Mares in temperate regions generally start cycling regularly in spring as the day-length and temperature increase, and then continue cycling throughout summer to the following autumn. Many mares stop cycling during the winter months as the days get shorter, and then start cycling again the following spring. Some mares, however, appear to cycle all year round - especially in northern parts of Australia.

The average length of the breeding cycle in mares is 3 weeks (19-22 days), which can be divided into two distinct phases. The period when mares are ‘on heat’ and receptive to a stallion is called the oestrous phase, which usually lasts 5-7 days. The hormone oestrogen is at a high level during this phase. The period between each heat is called the dioestrous phase, which usually lasts 14-15 days. The hormone progesterone is high during this phase, and mares are generally not receptive to a stallion.

The two female sex hormones - oestrogen and progesterone - strongly influence behaviour patterns seen in mares and fillies during the breeding season.

The length of the breeding cycle (as well as the oestrous and dioestrous phases) can vary between mares, and even at different times during the breeding season in the same mare. Likewise, behaviour problems can vary at different stages of the breeding cycle - some mares are worse during the oestrous phase (i.e. when they’re on heat), some are worse during the dioestrous phase, and some mares are difficult to manage throughout the whole cycle or are simply unpredictable in their cycling behaviour.

Could this problem be something else?

It is important to remember that behaviour in horses (and all animals) is made up of several components, including innate (genetic), learned (environmental) and sexual (hormonal). Some behaviour problems in horses are the result of genetics, poor training and/or past experiences, which can lead to bad habits.

In addition, some diseases can result in behaviour that may appear similar to what is observed during the breeding cycle. For example, a tumour in one of the ovaries can produce high levels of oestrogen, which may cause the mare to be constantly in-season; an infection in the bladder can result in the mare raising her tail and urinating frequently; and arthritis in the spine or hind legs can result in a mare frequently squatting down - signs that are also typical of a mare in season.

As with any other problem, it is important for your vet to establish a correct diagnosis before attempting to control or prevent a mare’s difficult behaviour - it may not be a behavioural problem at all, and treatment may be required for a different disease or condition.

How can I manage my difficult mare?

There is now an Australian vaccine that provides a new way to manage behaviour associated with the breeding cycle.

In the past, vets and horse owners have tried a variety of treatments and remedies in an attempt to control the breeding cycle in mares and fillies and to prevent problem behaviour. These treatments have generally involved hormone injections, oral hormones (given daily), herbal remedies and acupuncture.

The new Australian vaccine, like all vaccines, works via the horse’s own natural immune system and does not involve giving hormone treatments.