Published: July 2020 | Updated: February 2023
Foal heat is what we call the first estrus or mare heat cycle after foaling, and it usually begins 6-12 days after the foal is born, with the mare’s first ovulation occurring 10 days postpartum, on average.
Many breeders, especially those on large horse farms, choose to breed their mares back during foal heat in an effort to maintain a 12-month foaling interval, but is this the best plan for all mares? The answer to this question may depend on several different factors.
Advantages and Disadvantages of Breeding During Foal Heat
Breeding a mare back during this time can be advantageous for the breeder since he/she is optimizing the opportunity to get the mare re-bred. Foal heat breeding helps to ensure that the mare will maintain a foaling date around the same time each year since horses have an 11-month gestation period.
However, even if the mare loses the foal heat pregnancy, there is still often time to breed her again during that same breeding season. In some cases, it may also be necessary to breed on foal heat due to a stallion’s availability window–especially if he’s used in racing or competition.
One factor to note is that conception rates are typically higher in mares with relatively later as opposed to earlier foal heats. This is most likely related to uterine healing time. To that end, mares turned out on pasture tend to have quicker uterine recovery rates than mares kept stalled after foaling. Additionally, a younger mare (age 13 or less) is more likely to conceive during foal heat and also less likely to lose the pregnancy than an older mare.
In short, breeding mares during foal heat has been done for decades and still works well for many farms. But in some cases, it doesn’t work for the individual mare.
For example, some mares may not be physically ready to breed or may have poor conception rates if bred during their foal heat. Understandably, this can be due to what’s going on with her body physically post-foaling. During this time, the uterus sloughs placental debris, the lining of the uterus is restored, and the uterus, itself, shrinks back to its normal size. The more quickly the uterus can return to normal, the better the chances of success for foal heat breeding.
However, if the mare experienced a difficult birth or retained placenta, she most likely won’t be ready to breed during her foal heat, as she may have inflammation, infection, or fluid accumulation in the uterus and needs more time to heal.
Another thing to keep in mind is that some mares giving birth in very early spring may not have a foal heat at all, but instead have their first post-foaling heat approximately 30 days later (before resuming a 21-day cycle).
Foal Heat Diarrhea
One complication that occurs in about 80% of foals and often coincides with a mare’s foal heat is a bout of diarrhea, referred to as ‘foal heat diarrhea’ or ‘foal heat scours’.
While originally thought to be caused by changes in the mare’s milk due to hormones produced during the first estrus cycle after foaling, many veterinarians now believe this gut disruption in foals may be caused by normal but rapid changes in the bacterial and protozoal population within the gut.
Foal heat diarrhea also occurs around the same time that foals begin to nibble on the mare’s manure (known as coprophagy), as well as eat small amounts of hay or grain, so these may both be contributing factors as well.
Distinguishing Between Foal Heat Diarrhea and Infectious Diarrhea
Foals are often prone to bacterial, viral, and parasitic infections early in life due to their immature immune system. Likewise, if the quality or amount of colostrum from the mare was lacking, they may not have sufficient antibodies to protect them from pathogens. Foal heat diarrhea is not caused from an infection, however.
The main difference between foal heat diarrhea and other infectious causes of diarrhea is that newborns with foal heat diarrhea are typically healthy and alert. They will continue to nurse, remain active, and will not have a fever. Another difference is that foal heat diarrhea is usually mild and self-limiting whereas infectious-borne diarrhea is often profuse and watery.
Though most foals with foal heat diarrhea get over it fairly quickly, some may become ill, experience growth delays, or, in a small number of cases, die. Therefore, if your foal experiences severe diarrhea lasting more than a few days, has an elevated temperature (above 101.5 degrees F or 38.6 degrees C), or is not nursing regularly, you should consult with your veterinarian right away.
Foal Heat Diarrhea Treatment
While foal heat diarrhea is common and is usually a mild occurrence, it’s important to monitor your newborn closely to ensure that the condition does not worsen. If the area around the anus and rear end becomes irritated or there is some hair loss, washing the area with a mild soap, drying it, and then applying a topical protectant such as petroleum jelly or zinc oxide can help prevent further scalding. You will likely need to do this daily until the diarrhea resolves.
Likewise, administering probiotics specifically designed for foals, such as the FullBucket Foal Probiotic Paste, may also help combat the problem.
In fact, supplementing with probiotics during your foal’s first few months can help to ensure the early establishment of a healthy gut microbiome.
Knowing what’s normal during your mare’s foal heat and understanding foal heat diarrhea, as well as how to manage it, will help ensure that the postpartum period goes smoothly for your mare and foal.