Hey There, Honey!

In nature, mares have a high fertility/ conception rate since they are continually with a stallion who teases and breeds them at the best times. But few domestic horses are bred under natural conditions in pasture harems, and broodmare managers must detect when each mare should be bred. A successful breeding program depends on being able to determine when each mare is in heat and likely to conceive, whether she's being hand bred by natural cover or by artificial insemination.

Some mares are so obvious in their heat cycles that even if they hear a stallion's vocalizations they will show heat, says Carlos Pinto, MedVet, PhD, Dipl. ACT (theriogenology, or reproduction), an assistant professor at North Carolina State University. "Some older broodmares may show heat in their stalls without a stallion on the premises," says Pinto. "Some owners can tell when the mare comes in heat just because of her behavioral change, but some need closer contact for teasing.

"In our teaching herd, about 20% of mares can be identified in estrus without being teased, whereas even with a stallion, about 10 to 15% may not display signs of heat unless teased at close quarters," he says.

Teasing Procedure

A teasing rail, stall, or chute (safe barrier between mare and stallion) is often used. Pinto says the stallion is allowed to sniff and touch the mare, starting at her head, to see her first response. "Only after she's been teased face-to-face with him is he allowed to go to her hindquarters," he adds. "This is a natural behavior of stallions (as they would do if running with mares at pasture). We try to learn from observing stallions teasing in a pasture situation."

He added that problems arise if people think teasing is as simple as just putting a stallion close to a mare.

The teasing stallion is an important factor. "If he knows how to pasture breed, he'll be more effective," Pinto states. "He'll start to vocalize before touching the mare. He knows he must go to her head or shoulders first at an angle, to test her receptiveness, before touching her hindquarters."

He adds that an inexperienced or impatient stallion that goes right to a mare's hindquarters might get kicked, or endanger the handler. Even if he is protected by a teasing rail, if he goes aggressively toward her hindquarters, the mare might get scared, pin her ears, and kick. The observer might misinterpret this to mean she is out of heat.

Some teasers have not bred a mare before, so that could interfere with their actions toward a mare. "And if you have a maiden mare or a mare with a foal at side (and she's protective), it may be hard to properly interpret their behavior," says Pinto.

Some mares are timid and won't show heat if the teaser is too aggressive. A gentle teaser will often get better results in bringing out the true status of these mares.

Teasing and Fertility

"One of the major causes of infertility in mares is persistent mating-induced endometritis," says Pinto. "When a mare is bred, the semen itself and bacteria introduced during breeding will cause some inflammation. This mating-induced endometritis is transient and a normal mare recovers quickly, but some mares don't clear the uterus so efficiently; this causes persistent inflammation and infertility."

Pinto collaborated on a research project headed by Dale Paccamonti, DVM, MS, Dipl. ACT, professor of theriogenology in the Department of Veterinary Clinical Sciences at Louisiana State University, to determine if teasing causes an increase in uterine contractions and if that response varied by day of the cycle.

"Significant increase in intrauterine pressure (contractions) was observed in response to teasing, both two days before ovulation and on the day of ovulation," says Pinto.

This means when a mare is teased, it stimulates increased contractions of the uterus, and the contractions become even stronger around the time of ovulation. "This is one reason fertility may be decreased in artificial insemination programs, compared with mares in a herd with a stallion," he explains. "With all the teasing that goes on, and the mare being bred several times, she has contractions throughout the day and clears the uterus very well."

Mares with delayed clearance may be less fertile in an artificial system, Pinto adds. "Luckily, we have drugs such as oxytocin and prostaglandin to increase contractions, but this requires veterinary assistance. I'm not saying we should tease a mare several times a day to increase her uterine contractions and improve its clearance (this is usually not feasible), but this research helps us understand how teasing is directly associated with uterine contractions and, consequently, fertility."


Pinto says several studies have linked hormones to teasing. Some of the first research studies linking teasing to oxytocin release were done by two New Zealand endocrinologists and presented at the Sixth International Symposium on Equine Reproduction in Brazil in 1994. The research showed the act of teasing stimulates release of oxytocin in the mare, setting in motion many physiological actions that enhance ovulation and transport of egg and sperm to their proper destinations. Oxytocin, a hormone that stimulates milk let-down, also causes uterine contractions.

"The study we did here (at NCSU) to show that teasing causes uterine contractions was a follow-up on previous research that showed teasing to cause release of oxytocin," says Pinto. "We put electrodes in the uterus and vagina of the mare. We had a laptop computer getting signals from the uterus before, during, and after teasing. The mare could be in her stall, without being restrained. When the stallion was led by, she'd start to respond, and you could see the uterine contractions increase. These contractions are much lower during diestrus, when the mare is out of heat."

Research looking at patterns of behavior in mares shows that some mares that are usually strongly non-receptive will respond (showing heat) just by being passive. "Sometimes a subtle change in behavior is all you have to tell whether she's in heat or not," explains Pinto. "But this requires that you know the mare and have teased her regularly over several weeks. Even if you are not planning to breed her that month, it's important to keep teasing her in order to get more background information," he says.

Take-Home Message

Regular teasing of broodmares with experienced stallions will allow owners and broodmare managers to better interpret her signals of receptiveness to breeding, or heat. Research has also shown that regular teasing can help increase uterine contractions in mares, thus improving fertility in mares with persistent post-mating endometritis. 

Teasing Maidens and Mares With Foals

Many maiden mares don't show heat just because they are nervous, especially if they just retired from performance and have not fully adjusted to a new situation. These mares need a lot of careful teasing to get them to relax, and careful observation to detect subtle changes in behavior that might indicate heat.

Some mares in a herd might be afraid of bossier mares and won't come up to the stallion if they are being teased in the field, says Pete Sheerin, DVM, Dipl. ACT, of Rood and Riddle Equine Hospital in Lexington, Ky. "When you move farther down the fenceline with the stallion, those timid mares may show signs of heat," he says. You have to be aware of everything that's going on in the field, and know the social order of the mares, Sheerin says, adding, "Teasing mares is an art, and if you work with them long enough in the proper manner, most will eventually show heat."

Carlos Pinto, MedVet, PhD, Dipl. ACT, an assistant professor at North Carolina State University, says, "Special attention should be paid to mares with foals. Some people don't understand that when a mare is protective of her foal, she won't tease well. You may have to restrain the foal very close to her to minimize her worry about leaving it. If that doesn't help, you may have to restrain the mare by using a twitch, to take her mind off the foal. Some people think this would upset her more, but you'd be surprised at how many mares change their focus when twitched."

Sheerin says you can take some mares out of the stall and tease them away from their foals and they'll show. "You can't have the foal very far away or she'll become extremely agitated, but just having the foal temporarily away from her may get her to focus on something else, like the stallion," he says.--Heather Smith Thomas

One Breeder's Method

Bill Tracy, manager of Oak Tree Ranch near Bandera, Texas, uses a reliable teaser stallion he's owned for many years. "He was used for pasture breeding and is very savvy," says Tracy. "If he's really interested in a certain mare when we check them, you'd better go back again and tease her some more--because he knows--even if she's not showing. I walk him along the 12-foot-wide alley between the mare paddocks, and may let him stop and eat grass while my wife (with her chart) watches mares' reactions. Some mares come up belligerently to try to run him off, and others come up to show receptiveness. A more timid mare might stand off by herself and show heat. That's why it's important to have an observer. One person can't see everything; if you're watching the mares and not watching the stallion you'll be in trouble."

Tracy says a bossy mare might run other mares away even if she isn't in heat. He suggests walking by several times to know what's actually going on in a field. "It pays to be persistent, rather than just leading the stallion through once and deciding nothing's showing," he says.

When teasing along a fence, the fence must be safe and secure. Some mares will run up and kick or strike at the stallion and might get a foot caught or kick you or the stallion.

When mares are in the barn under lights, Tracy brings the stallion through the barn and teases at each stall. An observer can watch the mares in the other stalls. A timid mare might back away from the stallion at the door, but she might show heat when he's not at her stall.

Teasing mares with their foals present can be difficult. "We have a stud pen that's a quarter-acre (with six-foot-high pipe fence) within a larger, one-acre pen," he says. "I can turn mares in the bigger pen next to the stallion. I first saw this type of set-up at Texas A&M. They used it in their horse reproduction course, and someone could sit up on the corner of the fence with a chart and observe, writing down which mare came over or did what."

Keep identification on mares, such as a neck collar, so that anyone can properly identify them. "Sometimes the mares don't show heat when you are teasing them, but a little later someone will be out feeding hay and see a mare showing to another mare," says Tracy.

He says some farms leave a teaser stallion in a pen next to the mare paddock so mares can come up to him when they want. "I prefer being able to observe mares in a controlled situation," Tracy adds. "I've found that when the mares and stallion are very familiar with one another (constant contact), the mares may not show as much because it's no big deal."

The teasing situation works best if it's more of a novelty for the mares to have the stallion come by; a mare is more apt to come see him and say, "Hey, I've been looking for you!" --Heather Smith Thomas

About the Author

Heather Smith Thomas

Heather Smith Thomas ranches with her husband near Salmon, Idaho, raising cattle and a few horses. She has a B.A. in English and history from University of Puget Sound (1966). She has raised and trained horses for 50 years, and has been writing freelance articles and books nearly that long, publishing 20 books and more than 9,000 articles for horse and livestock publications. Some of her books include Understanding Equine Hoof Care, The Horse Conformation Handbook, Care and Management of Horses, Storey's Guide to Raising Horses and Storey's Guide to Training Horses. Besides having her own blog, www.heathersmiththomas.blogspot.com, she writes a biweekly blog at http://insidestorey.blogspot.com that comes out on Tuesdays.

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