Ask the Vet: Reproduction

Are you considering breeding your mare or stallion this season? Pose your equine reproduction questions for this month's AAEP expert, Dr. Semira Mancill.

1
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.
2
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.
3
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.
4
Question: I have a 7-year-old mare that has never been bred before but has a fused bone chip in one knee. Her knee is enlarged, with no heat, but she does walk lower leg turned in. She can still lay down and get back up but does so with her bad leg out in front of her and not bent under her. We have considered breeding but I am concerned about the additional weight on her knee, overall balance, and ability to get up/down. This is a race injury that occurred at 4-years-old. Would a pregnancy pose a problem for her?
Answer: 
The extent of your mare's comfort will dictate her being able to carry a foal to term without significant problems. If she's getting around with some problems and/or has pain, they will get harder on her in late pregnancy. Now, having said that, many mares with chronic lameness get pregnant and carry their foals to term. It's difficult to determine your mare's situation without seeing her and doing a proper examination. I would recommend having your veterinarian do a physical exam on her and give you advice on her situation individually. There is always the choice of embryo transfer (as long as her registry/association allows it), so you can have the foal and keep her comfortable as well.
5
Question: Is it true you can breed (or inseminate) a small mare to a much bigger stallion? Some say it is dangerous and others say the size of the mare's uterus will limit the size of the foal to a safe delivery size. If there is a limit in difference of size what is that limit?
Answer: 
There was a very interesting study done by Dr. Ginther years back, where he put "large" mare embryos into pony mares and vice versa. There was not any appreciable amount of problems with those mares foaling on either side. They then followed the foals out to their 3-year-old years and measured bone sizes, wither height, etc. There were some small changes, but the author felt that they were insignificant in the grand scheme. There are not any "rules" per say on sizes or limits. I would say that common sense would prevail in choices of mare size (probably wouldn't put a draft embryo in a mini!) but it shouldn't be a major problem as long as they are standard sized mares. I have bred many standard Quarter horse sized mares to Friesian studs and not had issues with those foals.
6
Question: My new broodmare, I hope to breed, has very large mammary glands from past breedings. Will this be a problem for a new born foal?
Answer: 
Sounds like you have a nice broodmare on your hands! Previous pregnancies can alter the maiden mare's mammary glands over the years, causing them to stay in a somewhat enlarged state. As long as she doesn't have signs of mastitis or infection of the mammary glands, such as heat, pain, or foul discharge, she should be just fine. Happy breeding season!
7
Question: My pastures tested 5% endophyte. Is it necessary to remove my mare that is due March 23rd, from the pastures completely? And if so, when? I'm concerned the stress of confinement would affect her.
Answer: 
To be absolutely safe, mares grazing on endophyte fescue should be removed 45 to 90 days before estimated foaling. Fescue toxicosis in pregnant mares can cause a variety of problems, including prolonged gestation, "red-bag" or premature separation of the chorioallantois, agalactia or reduced milk production with possiblity of decreased amounts of colostrum (critical to the foal's immunity in those first few months after birth), thickened placenta, retained placenta, among others. If your mare has a friend out in the pasture that could be a buddy in the stall next door, this may reduce her anxiety levels.
8
Question: I recently had a stallion go through a fence and cover two mares. What are the chances of a mare settling in January in Alaska? 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).
9
Question: My 10-year-old mare has MILK and as far as I know is NOT pregnant...she doesn't look pregnant either. She has had two foals before I purchased her 6 years ago. Should I be concerned?
Answer: 
There are several reasons your mare could have discharge from her mammary glands, including pregnancy, mastitis (infection in the gland), or some produce fluid for unknown reasons that are not harmful to the mare. If the mare is at your place with NO intact males, including young colts around in the last year, then pregnancy is probably low on the list. Mastitis can look as simple as just an increase in size of the mammary gland with some fluid discharge all the way to highly increased in size, hot, painful and include foul discharge. Although some mares can normally have fluid discharge without disease or pregnancy, a simple check-up with your veterinarian can rule out these reasons and give you an answer to let you rest easy about your mare.