Reproduction - Estrous Cycle and Teasing

estrus behavior | teasing methods | group teasing | individual teasing

The Estrous Cycle

Introduction: The reproductive cycle in mares is classified as seasonally polyestrus. This means that they are reproductively active at a defined portion of the year, during which they will cycle repeatedly. Each of these estrous cycles are driven by a coordinated system of interdependent hormonal responses that stimulate appropriate behavioral and anatomical changes. These changes combine to provide favorable conditions to establish and support pregnancy.

Estrus Behavior: The estrous cycle in mares is divided into two distinct periods, diestrus and estrus. During diestrus, progesterone produced by the corpus luteum is dominant. This period is characterized by behavioral non-receptivity and even aggression towards a stallion that approaches too closely. During diestrus, mares are commonly described as "out of heat." For most mares, diestrus begins at 1 to 2 days after ovulation and continues for 14-16 days.

Mares that are in estrus or "in heat," are primarily influenced by the hormone estrogen. Estrogen causes them to exhibit a receptive behavior when a stallion approaches. Mares that are in estrus will typically show one or more of the following behaviors:

Estrus typically lasts 4-7 days, beginning 4-6 days before ovulation and continuing 1-2 days after ovulation has occurred. However, the length of time that mares are in estrus is much more variable in late winter/early spring. During this period it is not uncommon for mares to remain in heat for up to 2 weeks.

Estrus behavior also varies between mares. Some mares consistently show strongly prior to ovulation, others may never show more than passively. The intensity that a mare shows estrus is usually not related to fertility. However, mares that consistently fail to show estrus can be difficult to breed and require more frequent palpation exams to continually determine where they are in their cycle.

Estrus behavior can also change in the same mare when exposed to the teaser stallion under different circumstances. Following are some examples of these circumstances and how teasing behavior may deviate from normal:


Teasing Methods

Introduction: The development of reliable methods to assess and record teasing behavior of mares is certainly one of the most important tasks undertaken at breeding facilities. Accurate and up to date teasing records are absolutely essential in the success of equine breeding programs.

Breeders typically use a scoring system to record daily changes in the teasing behavior of the mares in their care. One popular scoring system uses the numerals 0-4 to describe a mare’s behavior toward a stallion. Each teasing score corresponds to a type of reaction generally exhibited by mares and signals their readiness to breed (Table #1).

Table #1 - Example of a typical scoring system for estrus characterization in mares:

0 - Out of heat; mare aggressively rejects the teaser stallion.
1 - Passive; mare stands quietly and neither accepts nor rejects the
2 - Lightly in heat; mare stands and eventually displays estrus in response to prolonged exposure to the teaser stallion.
3 - Solidly in heat; mare stands and displays estrus in response to the teaser stallion.
4 - Strongly in heat; mare stands and strongly displays estrus in response to minimal exposure to the teaser stallion.

Estrus behavior usually becomes more pronounced as the follicle progressively develops. For many mares, estrus begins with passive behavior 4-6 days before ovulation, then teasing behavior will intensify as ovulation approaches. Teasing scores will usually be detectably reduced by 24 hours after ovulation; however, many mares will usually "tease in" for 1-2 days post ovulation.

A good teasing program uses a teaser stallion that is manageable and exhibits strong libido. Virtually any method is acceptable that can consistently and safely permit a stallion to have relatively free access to nuzzle a mare and provide an observer the opportunity to assess her receptivity to the stallion. Most breeders find the ability to effectively perform both individual and group teasing methods important since each method has distinct advantages and disadvantages. The importance of a sound and consistent teasing program to a successful breeding operation cannot be overstated. For the majority of mares, it is a very reliable and cost efficient method of evaluating estrus.

Group teasing: This method provides breeders an excellent means of following the cyclic activity of individuals within groups of mares. Mares in group teasing situations are given the opportunity to freely associate with the teaser for a period of at least 15 to 20 minutes. The advantages of group teasing include efficiency and effectiveness. Often an astute observer is given the opportunity to distinguish subtle changes in the mare’s behavior that may not be as noticeable in an individual teasing situation where the mare is restrained.

A major drawback of this method is that it often fails to detect estrus in mares that are either fearful of approaching the stallion or fearful of mares already near the stallion. This is especially true early in the estrus period and in maiden mares. For these reasons, the manager should keep in mind that as the number of mares teased in a group increases, it is more likely that observation of estrus in some mares will be missed. Generally, it is safe to begin the season teasing 10 to 15 mares in a group. Because some of the mares in each group become pregnant, this number may be increased as the season progresses. Another problem associated with group teasing is that mares that have been newly added to the group will often tend to stand quietly away from the others mares or keep close to a newfound friend. In these cases, the observer must make a special effort to take notice of any degree of attentiveness that the mare may express toward the stallion. In these situations, mares will occasionally need to be removed from the group and teased individually.

Individual teasing: These teasing methods are especially useful in breeding operations that employ hand breeding. For safety reasons it is essential that all mares be individually teased before the stallion is allowed to approach the mare.

Careful observation and recording of teasing characteristics are key to making appropriate breeding management decisions. Following are some of the most important factors to consider when assessing teasing behavior in mares:

Teasing should be performed daily until a mare is determined to be safely in foal. Afterwards, mares should be teased periodically through the rest of the breeding season. It is often an advantage to pasture pregnant mares near a stallion’s exercise pen. The benefit of this is two fold: it allows the stallion to be housed in a more natural setting near mares, while at the same time, allowing the manager to keep track of their teasing behavior. Mares that return to estrus can be removed and placed back into a more intense management scheme.