The First Steps in Breeding Your Mare

Many first-timers have been asking us what is involved in breeding mares – what are the steps involved from getting mares pregnant all the way through to having beautiful babies running around – there is a lot involved! But this week, since a lot of people are starting to think about breeding before the season beings around September, I thought I would talk about the first few steps in breeding your mare to a stallion of your choice (one of the Ebony Park boys of course!!!)

When you have decided to breed your mare, the first thing that needs to be done before you bred is to make sure your mare is cycling (showing signs of oestrus)!

To do this she will need to be teased with a stallion or gelding (or other mares also work sometimes!). The signs you want to look for are any combination of the following:

  • Squatting and urinating when being teased – the tail will be held up high
  • Allowing the teaser stallion to approach and smell her (especially her back end – be careful of legs!)
  • Winking of the vulva
  • Squealing when approached by the teaser

Once the mare has ovulated she will no longer show signs of being ‘in heat’ (oestrus) and will often become quite aggressive towards the teaser (so be careful!). If the mare is cycling normally, she will come back into heat within around 10-16 days after the end of the previous cycle (so she will be in heat for 4-5 days, with her cycles occurring regularly ever 21 days or 3 weeks in total).

So once your mare is showing one of more of the above signs that she is in heat, what do you do next? Ultimately, at some stage during the next few days, you will want to breed her, but when? Many of us are using shipped semen, whether local and imported, and want the timing to be just right so that we maximize the potential of our mare falling pregnant. The most effective way of ensuring this is to get the vet out once our mare is in heat, so that he can perform an ultrasound scan on the uterus and ovaries and determine whether she is close to ovulation. If she is not close to ovulation he may want to come back in a day or two to scan her again. If she is close to ovulation the following can be observed on ultrasound:

  • A dominant, large follicle on one of the ovaries (there are sometimes more than one large follicle) – it depends on the size of your mare as to what a ‘large’ follicle is, but generally speaking, this will be >30mm in diameter – for Friesians it can be over 40mm in diameter!!
  • Folding of the uterus, coupled with uterine oedema – the uterus should not have any fluid in it, but the folds of the lining become fluid-filled.
  • The cervix of the mare will become very soft, and will be what is described as ‘open’ – this means that we can actually get the semen in there without too much trouble!

Make sure you ask your vet what he/she is looking at when they are scanning if you are interested!!

Unfortunately, it is not always this easy to get your mare even to the cycling stage!!

The normal breeding season in the southern hemisphere for horses is between September- February (spring and most of summer), although some horses will continue to cycle before and after these times. If your mare is not coming into heat, often a hormone called prostaglandin will be used in an injectable form to try and make her cycle. Prostaglandins (PG) act to regress the corpus luteum (CL) on the ovary (this is producing progesterone, which in

general terms promotes gestation or pregnancy – something that is not necessary before she is actually pregnant!) – this allows the mare to enter into oestrus.

Note that PG does not cause the ‘heat’ of the mare, it just removes the system (corpus luteum) that is preventing oestrus. PG is only effective when administered at the right stage during the cycle. Therefore, generally the vet will ultrasound the mare before PG – the mare needs to have a CL in order for the PG to cause it to regress!!

Generally, in terms of nutrition when breeding a mare, as with all of our  horses, we don’t want her to be too fat or too skinny. However, there have been a number of studies conducted that suggest that mares on a rising plane of nutrition (i.e. they are putting on weight) fall pregnant more easily. So if your mare is looking a bit underweight when you breed her, this may not be a bad thing! That being said, we don’t want to starve our mares just to get them to put weight on when we breed them, or to make them too fat by raising the feeding rates! As long as the mare is healthy and happy, fingers crossed she will get pregnant!!

Good luck this breeding season, and make sure you click here to claim your FREE breeding pack if you are interested in breeding with one of our boys this year! 🙂

To Your Dreams Becoming Reality,

The Ebony Park Team