Mares: Love ’em or Hate ’em

If tHere’s a mare in your barn you know exactly what the title of this article means. Mares have proven themselves in every area of performance, but dealing with them successfully may require some special attention to hormonal cycles, despite proper training.

Mares go through their heat or estrus cycles in response to increasing daylight. Left to natural lighting, a mare will cycle from about April through October in North America. In a barn with lights left on late at night or all night, a mare may even cycle all year. Retired race mares are often ?put under the lights? for early foaling so their foals will be be more mature for the racing year calendar.

HEAT CYCLES. A mare?s estrus cycle runs about 21 days, and for 5 to 7 days of that cycle she will be ?in heat.? Frequent squatting and urinating with her tail flagged to one side and ?winking? of the vulva mark the heat period. If you’re lucky, those are the only changes that mark the heat period.

Mares tend to fit into one of three camps when it comes to their heats. Some mares barely show any changes in behavior or attitude towards work or other horses. Some mares lose all ambition and work ethic ?simply becoming blah and needing extra efforts on your part to get any work done. And some mares become very difficult to handle. These problem mares are sensitive to touch, may kick without any real provocation and may become aggressive to other horses or to human handlers.

It can be frustrating to have your top equine athlete be a mare who really doesn’t train well for one week out of every three, and horse owners have looked for solutions over the years. Note: Some of the suggestions below will not be considered legal for competition. Check your rule books.

SOLUTIONS. If you aren?t planning to ever breed your mare, consider sterilization by having her ovaries removed. Yes, this is a drastic step but it is also a permanent solution. When a mare is ?spayed,? just her ovaries are removed, not her uterus. This is usually done via flank incisions. Not all veterinary clinics do this, you may need a referral. Cost is usually under $1,500.

Before you take this big, expensive step, be sure that your mare?s irritability is related to her heat cycles. She may actually be in pain from some other ailment.

Pneumovagina (air being sucked in to the vagina due to poor conformation or stretching during work) can cause behaviors that mimic many of the ?bad? in heat behaviors due to discomfort. In those cases, Caslick?s surgery with sutures to tighten up the vagina can solve the problem.

Back problems, kidney problems, tying-up and mild recurrent colic may all mimic the irritating pain some mares feel during their heats. An ovarian tumor could cause pain and erratic behavior, and your veterinarian may be able to do a screening blood test (testosterone level) to help determine if this is the cause. The point is, you need to rule other causes of pain or erratic behavior before treating for ?in heat? causes.

If your mare is simply irritable right at the day of ovulation, pain medications may be the way to go. Your vet may prescribe Banamine, which can often keep your mare comfortable for the day or two that she is uncomfortable.

Then you get down to hormonal solutions, also from your veterinarian. Your goal is to cover up the hormonal fluctuations or stop them with externally added hormones. Regumate is the most commonly used hormone for mare-heat problems. This is a progesterone drug, so it stops the heat cycles, basically ?faking? a pregnancy in your mare. With some mares this works very well?for others there is a major loss of drive and willingness to work. Women must handle this drug with care as it can effect human cycles, too.

Whether or not there would be long-term effects on your mare?s reproductive soundness is uncertain. Many mares do become pregnant after stopping Regumate therapy, but it isn?t a sure thing.

Another hormonal manipulation is HCG or human chorionic gonadotropin. Injections of this hormone cause ovulation and repeated injections can control estrus behaviors.

A new treatment for hormonally challenged mares is a vaccine called Equity, which stimulates an immune response against GnRF or gonadotropin releasing factor. The mare?s ovaries become small and inactive, mimicking the winter period with no heats. The vaccine is said to be effective for three to six months but some mares show longer effects. This isn?t recommended for use in mares that you would like to breed eventually.? However, Equity is currently only available in Europe, not North America.

If all of those solutions appear overwhelming, but your mare is kicking her stall door relentlessly, you may want to look into herbal preparations that have been effective for many horses. Vitex, also called chaste berry or monk?s pepper, doesn’t totally stop estrus or estrus behaviors. It does modify them, however, through the phytoestrogens which are part of the herb. For mares with irregular cycles, this herb may stabilize things and it does seem to have a ?mellowing? effect on many mares.

Herbal compounds and medications that tranquilize or mildly sedate a mare can cut down on aggressive behaviors as well.

The traditional ?calming? supplements?magnesium, thiamine (vitamin B1), tryptophan, valerian?may make a difference, when given at proper dosages.

BOTTOM LINE. If your mare has problems related to her heat cycles, you have options?ranging from permanent surgery to daily herbal supplements during the estrus cycles. Consider your riding goals, breeding goals and any health problems your mare has to find the best solution for your mare.

Article by Consulting Veterinary Editor Deb M. Eldredge, DVM.

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