Welcome!

We are announcing the addition of a regular newsletter available to our clients. This newsletter will be available online at our website www.reidequine.com and emailed to those on our mailing list. Here you will find articles on management and care of your horses as well as recent updates about our practice and doctors. Feel free to forward on to your friends. If you would like to be added to our mailing list please email Brenda at byvet@comcast.net.

Estrus Suppression in the Performance Mare

Horse owners, trainers, and veterinarians are all looking for easy, inexpensive, and effective methods to block behavioral estrus in performance mares. Some mares are more difficult to train or exhibit performance issues when in heat. A small number of mares may experience pain or colic due to a large follicle or recent ovulation. The following article will address a number of medications and management strategies available to suppress estrus in mares.

Mares are seasonally polyestrus, which means they have regular estrus cycles that coincide with long daylight seasons. During the winter, most mares (80%+) are in anestrus, which means that their ovaries have very little activity and therefore they show very little or no estrus signs. As daylight hours increase, there is increased ovarian activity resulting in the spring transition in February and March when mares start producing follicles.

By spring and summer, mares exhibit regular estrus cycles that last about 21 days, 5 to 7 of which the mare is showing signs of being in heat. Closely tracking a mare’s estrus cycle on a calendar is probably one of the easiest and cheapest methods to diagnose behavior issues related to the heat cycle.

It is important, however, to rule out other causes of poor or unwanted behavior. A thorough general physical and reproductive examination, with ultrasound should be carried out. There are a number of ovarian disorders that can result in anything from no estrus cycling to extreme stallion-like behavior and aggression. One type of ovarian tumor, called a granulosa cell tumor, can reach basketball size and can produce high levels of testosterone leading to undesirable behavior. Measuring levels of different hormones in the mare may also be part of this diagnostic process.

Most importantly, getting the right diagnosis for the behavior issues can save money in the long run by reducing the incidence of inappropriate treatments.

There are several treatment options, both medical and surgical, to suppress estrus behavior in the mare.

Progesterone/Regumate®

The most common treatment for estrus suppression is the administration of some form of progesterone.

Oral altrenogest (Regu-Mate®) is the most commonly used product for estrus suppression. This synthetic progestin reliably keeps mares in diestrus and prevents them from coming into heat. In addition, it’s the only approved synthetic progesterone for estrus suppression in mares. Unfortunately, Regu-Mate® requires daily administration and careful handling, as it can be easily absorbed through the skin and affect women’s menstrual cycles. Compounded long-lasting (up to 30 days) injectable formulations of altrenogest are becoming increasingly available and more common in use. Cost can be a factor with long-term use.

Injectable forms of natural progesterone in oil will also suppress estrus in mares, however these require daily administration, and some mares develop muscle soreness after progesterone injections.

Depo-Provera® is the brand name of the synthetic progestin hormone medroxyprogesterone. The drug has been administered to performance mares with the intention of blocking behavioral estrus. However, extensive research has shown that is it NOT effective at suppression of estrus, has no effect on ovarian activity and cannot be recommended for estrus suppression in performance mares.

Intra-Uterine Devices

A 35-mm glass marble placed in the uterus within 24 hours following ovulation will result in a prolonged luteal phase in approximately 40% of mares. Progesterone levels remain elevated in these mares for up to 3 months, effectively suppressing estrus for this length of time. The cost is relatively low and drug-free, however, since this works only 40% of the time, it is often not reliable enough for the performance mare.

Ovariectomy

A permanent procedure, ovariectomy can be performed to remove the mare’s ovaries. It can be done on the standing sedated horse through a few small holes in the flank (laparoscopic). This procedure cannot be reversed; therefore a correct diagnosis should be made first. The upfront costs are higher than other procedures, but the results last forever and could save money in drug costs later on, especially in mares that are very active in competition. Cyclicity will cease following the procedure, however estrus behaviour may not in some mares. A mares behaviour during anestrus (winter) will most closely approximate how she will behave after ovariectomy, as this is the time her ovaries are quiescent.

It is most important for an owner to thoroughly investigate the cause of the mare’s behavior; and only after ruling out other causes should he or she assume that the behavior is solely related to the mare’s estrous cycle. Careful documentation of the mare’s behavior and a veterinary examination are necessary to determine the best treatment for each mare.

Dr. Erin Newkirk

August News

Dr. Raul Casas recently returned from his annual Humane Society Veterinary Medical Association Field Services Program (HSVMA) trip. Formerly Rural Area Veterinary Services(RAVS), this non-profit veterinary outreach program combines community service and veterinary education to bring free veterinary services to underserved rural communities where poverty and geographic isolation make regular veterinary care inaccessible.


This year’s trip was to Guatemala, where Dr. Casas volunteered his time and expertise during the 9 day trip to help provide veterinary care and improve welfare to the country’s working horses. If you would like to learn more about other HSVMA membership and programs please visit www.hsvma.org

Introducing Our Newest Interns!

We are pleased to announce the arrival of our two newest interns: Jodie Stowell, DVM from Tennessee and Nikki McGreevey, DVM from Colorado.

 Dr. Jodie Stowell

Dr. Nikki McGreevey

Both of our interns live either on site or just around the corner and are responsible for the primary care of your equine should it ever need to stay with us. The interns are also an important part of our team and work side-by-side with our doctors in the ambulatory or hospital care of your horse. Should your horse need emergency treatment after hours, they will likely be the first to meet you and start necessary treatment. Each intern spends about a year working in this role and Reid & Associates appreciates all that they do here to help care for our patients.