Oestrus-related behaviour in fillies and mares

Behaviour and temperament problems associated with the oestrous cycle (reproductive cycle) are a very common complaint of owners, riders, trainers and handlers of fillies and mares. Many fillies and mares become extremely cranky and difficult to handle when they are 'in-season' or 'on-heat'. This behaviour pattern in fillies and mares when they are cycling is also known as 'horsing' or 'marey behaviour'.

The reproductive cycle of most mares is regulated by day-length, as well as by nutrition and climate. Most mares in temperate regions commence cycling in spring, as day-length increases, and this continues throughout summer to the following autumn. However, some mares do appear to cycle all year round, especially in more tropical regions.

The commonly observed signs associated with the oestrous cycle of fillies and mares may include some or all of the following:

  • Clitoral/vulval 'winking' or 'showing'
  • Frequent urination
  • Wet tail and hind end
  • Tail raising
  • Squatting down, dropping hips, adopting breeding posture
  • Squealing
  • Aggression and kicking, ears back
  • Increased interest in nearby stallions and geldings
  • Decreased co-operation or concentration during training, performance or racing
  • Difficulty in handling
  • Nervousness and anxiety
  • Unpredictable behaviour

Zoetis has recently developed a world-first vaccine that can be used to effectively control oestrus and oestrus-related behaviour in most fillies and mares. This vaccine is now available in Australia through veterinarians. For further information on this new vaccine, and to find out whether it is appropriate for your filly or mare, please consult your local vet, or call Veterinary Operations at Zoetis, on 1800 814 883.

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