Wellness Tips

Equine Reproduction

Murdoch Veterinary Clinic has a wide range of experience with regards to equine reproduction. The clinic’s facilities, ultrasound machine, and other veterinary instruments enable us to perform procedures ranging from thorough prebreeding exams to pregnancy diagnosis at 14 days post-breeding.

Clients and their mares have had many successes with the assistance of our clinic and each year more people have been requesting equine reproductive advice and services. Initially many horse owners are overwhelmed by the scientific lingo used by the vets so this brochure has been designed to explain both the terminology and services offered at the clinic.

Answers to Frequently Asked Questions

1. Why does the vet always put his or her arm up the mare’s bum?

By placing a hand in the mare’s rectum, the veterinarian can actually feel most of the reproductive tract including the uterus and ovaries (see figure 1). The act of feeling the abdominal organs through the wall of the rectum is termed “palpation” and it allows the doctors to evaluate the health of the reproductive tract and determine the stage of the heat cycle.

Figure 1: The Mare’s Reproductive Tract

2. What is the equine estrus cycle?

Estrus is just a veterinarian term for heat. The duration of a mare’s heat cycle is measured as the time from the beginning of one heat to the beginning of the next. As the days get longer in January and February mares start cycling irregularly. Later at the peak of the breeding season in June the cycle repeats itself consistently every 21 days. In September and October cycles again become variable and by November cycling may cease altogether.

Signs of heat are best observed in the presence of a stallion and include:

The length of heat ranges from 2-12 days between mares, but each individual mare tends to be very consistent.

3. When should a mare be bred?

Starting on the second day of heat, breed every other day until the mare no longer accepts the stallion.

4. What is A.I.?

A.I. is short for artificial insemination. It involves collecting sperm from a stallion and then placing it directly in the mare’s uterus. AI is performed at a precise moment in the heat cycle just before an egg is released. The procedure is increasingly popular because the semen can be shipped by air from far away breeding farms that have highly prized stallions.

B. The Ultrasound Machine

Ultrasonographic images greatly help the veterinarian determine a mare is in her cycle. A scanner is placed in the rectum which then sends a picture of the reproductive organs to a video screen. The value of this expensive piece of equipment is obvious if you consider the ovarian changes which occur during the heat cycle (see Figure 2).

At the onset of heat, a developing egg is present on one of the ovaries. Ultrasonographically this is visible as a large black fluid filled bubble which is called a “follicle”. In most mares the follicle bursts at some point in the last two days of heat. The egg is then released into the uterine horn where fertilization takes place provided a sperm is present. Meanwhile the mare comes out of heat and the ruptured follicle converts to a dense white structure called a corpus luteum or “CL” in veterinarian talk. The CL is important because it produces a hormone called progesterone that is required to maintain pregnancy. In the event that pregnancy does not occur, the CL disappears by day 18 of the cycle and a new follicle begins to develop.

Close monitoring of ovarian activity is essential whenever artificial insemination is attempted because the sperm must be placed in the uterus just prior to follicle rupture and egg release (veterinarians call this release “ovulation”). To make things more complicated, cooled sperm prepared for shipping remains viable for only 48 hours. Therefore, the veterinarian requests the breeding farm to courier freshly collected sperm only when ultrasound reveals that the mare is about to ovulate.

Figure 2: Ovarian Changes

C. Reproductive Services

1. Prebreeding Exam

Mares may develop adhesions, infections, and other abnormalities which seriously decrease their chances of a successful pregnancy and foaling. The prebreeding exam involves rectal palpation, ultrasound, and examination of the cervix to detect any problems. Additionally, uterine fluid is tested for the presence of unwanted bacteria. All mares to be bred by A.I. must have prebreeding exam.

2. Artificial Insemination

This is a very rewarding service for both clients and veterinarians. It does, however, require significant commitment in terms of time and fees which arise from:

  1. The breeding contract with the stallion’s owner
  2. Courier fees to fly the fresh semen to Prince George and return the valuable storage containers
  3. Veterinary services

If a client does decide to A.I. a mare, Murdoch Veterinary Clinic is prepared to follow the mare closely which often involves ultrasounding mares on weekends and at nights. Our success rates in the past have been high so clients can expect a good outcome even though there are no guarantees when working with animals.

When considering A.I., bear in mind that the process is more intensive than simply sending a mare away to get bred. Be ready to work with your mare, the veterinarian, the breeding farm, couriers, customs officials, and airlines. Problems may arise from missed flight connections, poor sperm quality due to duration of transport, and connections may increase the chances of viable sperm being delivered to Prince George.

Clients are advised that A.I. requires planning before May when the mare will be coming into regular heat cycles. A list of steps to take in preparation for A.I. are listed below:

  1. Notify Murdoch Veterinary Clinic of your intent on getting A.I. done.
  2. Select a stallion and finalize the breeding contract.
  3. Give the clinic the name of the breeding farm so semen can be ordered when the mare is about to ovulate.
  4. Get the prebreeding exam done.
  5. Count on the mare requiring at least 3 ultrasound exams to determine when she will be ready for A.I.
  6. Do not expect all mares to catch on the first A.I. Remember that we can always try again the next time she comes into heat.

3. Pregnancy Diagnosis

Pregnancy can be detected 14 days after breeding with the aid of ultrasound. The developing embryo is visualized as a black fluid filled bubble in the uterus.

4. Boarding at Dr. Murdoch’s

In the event that the mare is quite far from Prince George it may be more convenient to board the prospective mother at Dr. Murdoch’s place. This allows frequent ultrasound monitoring so A.I. can be timed just right.

Mares about to foal can also be boarded in the care of Dr. Murdoch. She offers video surveillance and immediate veterinary attention should problems arise.