Hormonal Mares

Kate Hore RNutr (Animal) : Nutritionist at NAF

Owners of our mare friends will tell us, that while ‘Girl Power’ can be an unbeatable force in the arena, owning a mare can bring it’s own, unique, challenges - sweet and lovely one day, ears pinned back and uncooperative the next! As an ‘entire’ it can be more like competing with a stallion than a gelding. As riders we need to be aware of
her hormonal challenges, and know how we can help her through them. If she is experiencing seasonal problems the last thing on her mind is working well, so how do we regain control?

The veterinary approach of using the horomone, progesterone, to suppress your mare’s system is far from ideal. Owners find regulating with progesterone expensive, and it’s important to remember that it also carries a risk of affecting your own hormones through handling. Certainly women and girls who may wish to conceive in the future, should handle equine progesterone with extreme caution. The once common practice of vets inserting a uterine marble to trick the mare’s hormones into believing she was pregnant, and so not cycling, is now not so widely recommended. Researchers are finding the presence of this foreign body, the marble, in the mare’s uterus is commonly associated with endometritis, pyometra and infertility.

Mares typically exhibit anoestrus over winter, returning to regular oestrus from early Spring, cycling, on average, every 21 days. However as they go through that vernal transition they may exhibit extended periods of oestrus, meaning the early seasons are often the most challenging, so it’s good to be prepared.

What signs might we see? The ovaries are behind the saddle and below the spine, so discomfort in that area affects her ability to use her strides and easily lengthen over her back. Hormonal behaviour traits may also affect her focus or willingness to work. Owners should consider those management and dietary steps we can use to support her comfort whenever she is working and competing.

Check Body Condition Score, as excess weight can impact her cycles. Research finds obesity decreases the time
a mare spends in anoestrus, so meaning she is likely to cycle for longer, even all year round. It is also advised to review her stabling regime. Anoestrus is principally dictated by shorter day length, so if she is stabled somewhere with artificial lighting, particularly late in the day, then that may also mean she cycles all year round. Conversely,
this technique is used to promote oestrus and reproductive behaviour in Thoroughbred mares, where the breeding season starts in February, simply by using artificial light for those broodmares in the relatively dark Northern Hemisphere during that period.

Nutritionally, feeding a high fibre, low cereal diet is recommended. Avoid feeding starchy concentrate feeds which are associated with a number of health concerns, including increasing reactive behaviour, and so are likely to exacerbate the behavioural response to cycling seen in your mare.

Targeted nutrition is advised. Recent research in horses has shown that when dietary magnesium is combined with the right herbs it can improve focus and trainability. For hormonal mares those herbs should be those recognised
as associated with hormonal function. Often herbs that the natural plains dwelling horse evolved to self-select,
our modern mares now rely on us, as owners, to replace what is lost in the restricted culture of modern pasture.