Ask the Vet: Reproduction

Question: Is there an age limit for a mare to be fertile? I have a mare that I am unfamiliar with her history. I am also uncertain that she has had a cycle in the last 4 months. She is11-years-old.

Answer: There is no set age limit in mares as some mares can be fertile into their 20’s. Your mare is not old, by fertility standards. This time of year is tricky for horses. They go into a “quiet” time for fertility, called anestrus, in the winter, when they don’t cycle at all. Then, in the spring as the days begin to get longer, they will transition into cyclicity once again. So, your mare is likely right on track as horses are “long day breeders.” A simple palpation/ultrasound by your veterinarian can tell you where your mare is in her cyclicity.

Question: I recently had a stallion go through a fence and cover two mares. What are the chances of a mare settling in January? Is there a shot that can be administered to prevent pregnancy?

Answer: Although most mares go through a time where they do not cycle in the winter, there is no way for you or I to know for sure if those mares were fertile or not without an examination. There is a prostaglandin injection that your veterinarian can give to the mares if they are pregnant. A simple palpation +/- ultrasound transrectally by your veterinarian can tell you whether those mares are pregnant as early as 9-10 days after the mare ovulates (goes out of heat).

Question: How soon after delivery can a mare be bred back to another stallion? What are the positives and negatives for not allowing suitable time for recovery from foaling?

Answer: Most mares foaling during the breeding season (long days), will come back into heat around day 7 after foaling. This is called their foal heat. The foal heat can be a fertile cycle to breed her, as long as there were no major complications during foaling. Pros can be getting your mare in foal earlier in the year. Some issues that may complicate a foal heat breeding would be trauma to the reproductive tract during foaling, retained placenta and complications from that, exceed fluid or debris that hasn’t been pushed out. Sometimes there is added difficulty in retrieving an embryo from a bigger uterus on a foal heat breeding before it returns to its normal size once again. In my practice, I encourage a full examination of the mare’s reproductive tract to look for these potential issues and that’s a great time to get the foal examined again too. We breed many mares each year on foal heat and have great successes with it.

Question: Will Equi-Max dewormer be safe for my breeding stallion? On the back we noticed a “Not recommended for breeding Stallions”…. But I want to rotate my dewormers as to be thorough with my parasite program, especially with the weather warming up again. Can you tell me if this product is truly unsafe to use on a breeding stallion or a colt intended for breeding?

Answer: I have a box of EquiMax by Bimeda here and the label reads “Stallions and breeding, pregnant or lactation mares may be treated without adverse effects on fertility.” So, you should be fine to deworm with this product in your breeding stallion. To be safe with any product, I recommend to always follow the label’s directions.