Should You Rebreed Your Mare on Foal Heat?

About this time every year, as mares foal, mare owners begin to consider rebreeding on foal heat (estrous), rather than waiting for the 30-day estrous.  Wanting to move the birth-date of next year’s foal up a couple of weeks is an option that horsemen have considered for decades. When weanling and yearling halter futurities were popular, early foals were highly desired.  Thoroughbred breeders, especially those breeding for the sales ring, seek early foals as well while racing soundness and success, is less affected by an early birthdate.  If you are considering breeding your mare on foal heat, ask yourself two questions:  1. What do you actually gain by moving the breeding date and resulting foaling date up approximately 3- weeks?  2.  Is there anything to be gained by waiting until the 30-day foal heat?

 

Let’s look at the first question, what do you actually gain by moving the breeding date and resulting foaling date up approximately 3 weeks?  The first answer to this question is actually found in the question itself, by breeding your mare on the foal heat, the foal is born approximately 3 weeks earlier the next year, than it would have been had you waited to breed the mare during the 30-day heat.  Of course, this assumes the mare conceives on either of those heat cycles. 

 

The second advantage to breeding mares on foal heat is that the mare is less likely to return to anestrus (period of reproductive inactivity) following the foal heat.  If the mare does return to anestrus post foaling, it may be 2-3 months before she is physiologically ready to be bred.  So, these are the primary advantages of breeding on foal heat, what are the disadvantages? 

First, comparing mares bred for the first-time, postpartum, on either foal heat or on a 30-day or later heat, mares bred on foal heat have a lower pregnancy rate.  Second, postpartum mares bred on foal heat, lose a greater number of the resulting pregnancies than mares bred on or after the 30-day heat.  This information alone, suggests that waiting to breed mares on the 30-day postpartum estrous, may result in greater reproductive efficiency (pregnancy and then carrying the foal to term).

 

In the week or two after parturition (foaling) occurs, the reproductive tract goes through a period of cleansing and recovery.  The length of time required for post-foaling recovery may be determined by the ease of the foaling process, the level of trauma to the uterus during foaling, and the timely passage of the placenta, among other things.  Therefore, not every mare is a good candidate to be bred on foal heat and even if the mare becomes pregnant off of that breeding, chances of carrying the foal to term are generally less than if the mare were bred on the 30-day or later heat. 

 

If the mare undergoes a normal foaling, the placenta is passed in a timely manner, the mare carries good body weight, and a breeding exam by a veterinarian indicates the reproductive tract has recovered sufficiently, then breeding on foal heat may be a reasonable option.  If the breeding soundness exam indicates the mare could use a week or two of further recovery before breeding, you have little to lose by waiting.  In this situation, if you breed the mare on foal heat and she later loses the pregnancy, you may lose the entire year, only to start over the following breeding season.

                                                                                            Mike Yoder, Ph.D., PAS