Equine Breeding Terms Explained

Image courtesy of siggakr.
Image courtesy of siggakr

It’s that time of year again foaling and breeding time! The most exciting time of year for horse breeders, as well as the busiest and most exhausting.

Over the years I have found myself explaining to many horse owners the steps and procedures involved in breeding a mare. I know that sometimes it can be hard to understand and remember the meaning of all the terms that you hear or see on a veterinary bill. So whether you’re a first time breeder, an owner, work with horses or an old timer here are some of those common terms that you are going to hear and use during the breeding season and what they mean.

Waxed Up  – Is a term used to describe when a mare develops droplets of colostrum on her teats that look like beads of wax. This can occur when foaling is imminent or even as early as two weeks prior to foaling or sometimes not at all.

IgG – Stands for Immunoglobulin Type G or sometimes called Gamma Globulin G. An IgG Test or a Gamma E Check Test involves taking a blood sample from the foal at 12-16 hours of age. It is used to determine if the foal has received and absorbed enough of the important antibodies that are passed through the mare’s colostrum.

Flush – A uterine flush is usually performed on a mare post foaling, if she has a uterine infection or sometimes after breeding. It involves a vet feeding a catheter (long thin tube) through the vulva to the uterus and then putting liquid through it and into the uterus. A flush can be done with water or saline and it can be mixed with iodine or antibiotics if there is an infection present.

Scan – A scan is done using an ultrasound that is guided through the rectum to examine the mare’s reproductive organs. Scans are done a regular basis to determine the stage that a mare is in of her reproductive cycle by looking at the ovaries and follicle size. Scans are also performed to determine and monitor pregnancy.

Follicle Test (FT) – Follicle Tests are the most accurate way to determine when a mare will be ready to breed. The vet will use an ultrasound and scan the follicles to see what size they are and when they will be ready to ovulate which can help calculate when will be the best time to breed the mare.

Corpus Luteum (CL) – is a structure that develops in the ovary after ovulation. It produces progesterone and oestrogen which are hormones necessary to support pregnancy. If pregnancy does not occur the CL will regress within a few days. If pregnancy does occur it will remain for a few months and continue to produce hormones to support the pregnancy.

Oxy (Oxytocin) – is a medication given to the mare to make the smooth muscle tissues of the uterus contract which then helps rid the uterus of any fluid. It is often given post foaling, after a flush and sometimes after breeding.

PG – is short for Prostaglandin which is a hormonal injection given to mares to help bring them into heat as quickly as possible. Prostaglandin also causes luteolysis (the regression of the corpus luteum) which then helps to shorten the luteal stage and shorten the cycle.

Swabs – mares may require a clitorial and/or uterine swab to ensure that no infection is present prior to breeding or to determine if or what infection is present. A simple swab is taken of the area and it is then sent away to a laboratory for testing.

Caslicks – is a procedure that involves stitching closed the upper part of the mares vulva. Caslicks are performed to help prevent reproductive system infections that can occur due to a mares poor confirmation, previous foaling injuries or from sucking air through the vulva. Caslicks must be removed prior to foaling and serving to prevent the stitches and vulva from being torn and damaged.

Serve or Serving – this is the process of mating a mare to a stallion.

AI – is short for Artificial Insemination, which is when a mare is inseminated with semen that has been collected from a stallion. The semen can be used fresh, chilled or frozen and is inseminated into the uterus when the mare is ready to breed.

I hope this has helped you to know and understand some of the common horse breeding procedures and terms. If you have any further questions or concerns about your horses or breeding speak to your veterinarian, I am sure they will be happy to help.

Until next time,


Author: Bec

From a very young age Bec has always had a great love and appreciation for all animals. Bec is a qualified Veterinary Nurse and also has a Bachelor in Applied Science Animal Studies with special interest in Wildlife and Recreational Animals. Her studies have been put to good use working in various animal industries including small and large animal veterinary clinics, horse studs and the family cattle property. Horses have played an important part in her life, living on a horse stud and caring for horses throughout breeding, foaling, spelling, racing and retirement. Bec is the proud mum of two gorgeous girls, a beautiful Cocker Spaniel, chickens and many horses including a cheeky little pony.

2 Replies to “Equine Breeding Terms Explained

  1. More important than the percentage of mares who conceive on foal heat is percentage of live foals from foal heat breeding, which I think is only around 35%. Has this statistic changed? From my perspective, foal heat breeding is a poor practice when using no-guarantee frozen semen.

    1. Hi Wasim,
      Thank you for your comment. I don’t disagree with you, foal heat (in my opinion) is not the most optimal time to breed a mare, however every situation, mare and breeding program is different. I am not aware of the statistics on live foals from mares bred in foal heat. I imagine it is a hard statistic to measure as there are a number of other factors influencing this and it probably varies in different breeds, breeding circumstances and industry’s. Perhaps I will look into the statistics in a future blog.

      Kind Regards

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