Choosing to Breed During Foal Heat

If a barn full of people were asked their opinion about breeding a mare during foal heat, a barn full of opinions would result. This topic has been controversial for a long time. There is debate about whether it is harmful to a mare’s health,
Share
Favorite
Close

No account yet? Register

ADVERTISEMENT

If a barn full of people were asked their opinion about breeding a mare during foal heat, a barn full of opinions would result. This topic has been controversial for a long time. There is debate about whether it is harmful to a mare’s health, whether it negatively impacts fertility, and whether it causes an increase in fetal loss during pregnancy. Unfortunately, there have only been a handful of good-sized scientific studies published that thoroughly evaluate the practice.

So, is there any reason to breed during foal heat?

What is Foal Heat?

“Foal heat” is the term used to describe the first estrus or heat that occurs after a mare delivers a foal. During this time the mare ovulates and can become pregnant again. Typically, estrus occurs every 21 to 22 days in the mare and lasts four to seven days. A large follicle develops on an ovary, growing to a size of 35-55 mm or more in diameter. Most mares will show behavioral signs of heat throughout estrus, including signs of interest in a stallion, squatting to urinate, and “winking” to show the clitoris. It is not until the last 24-48 hours of estrus, however, that the follicle ruptures and ovulation occurs. Only then is the mare able to conceive.

The process of foaling stimulates the mare to begin cycling within a matter of days. The typical interval from the time of foaling to the beginning of foal heat is eight to 12 days. Some mares enter foal heat sooner. Interestingly, season of the year plays a role here. Mares that foal early in the year, from January to March, tend to experience a longer interval; they reach foal heat about 15 days after foaling. In comparison, mares foaling later in the season, in April and May, tend to have the shortest interval, about six to seven days. Research has shown that optimal conception rates are achieved when mares are bred at least 10 days after foaling. Therefore, if a mare enters foal heat too early, ovulation might occur before this 10-day point and before breeding is recommended

Create a free account with TheHorse.com to view this content.

TheHorse.com is home to thousands of free articles about horse health care. In order to access some of our exclusive free content, you must be signed into TheHorse.com.

Start your free account today!

Already have an account?
and continue reading.

Share

Written by:

Susan Piscopo, DVM, PhD, is a free-lance writer in the biomedical sciences. She practiced veterinary medicine in North Carolina before accepting a fellowship to pursue a PhD in physiology at North Carolina State University. She lives in northern New Jersey with her husband and two sons.

Related Articles

Stay on top of the most recent Horse Health news with

FREE weekly newsletters from TheHorse.com

Sponsored Content

Weekly Poll

sponsored by:

Where do you primarily feed your horse?
312 votes · 312 answers

Readers’ Most Popular

Sign In

Don’t have an account? Register for a FREE account here.

Need to update your account?

You need to be logged in to fill out this form

Create a free account with TheHorse.com!