Ask the Vet: Preparing Your Mare for Breeding Season

Answered by Madison Seamans, DVM, MS, Cornerstone Equine Medical Service, Wilder, IdahoCourtesy of AAEP

Question: What causes an 18-year-old maiden mare (never bred) to have a full bag from which I can squeeze liquid? In about October or November, she had a full bag for about a week, first time in her life that it’s ever been that full; then it went back to normal. I’ve had her since she was born, so I have the opportunity to observe her year around, every year. I also have an 11-year-old gelding in the herd. 

Answer: Mammary development, or what looks like it, can occur due to several reasons. First, the mare is pregnant. You should have a veterinarian perform a pregnancy exam to be absolutely sure.  There are many cases where “she can’t be pregnant, there is no stallion around!”, but the mare, indeed, was “expecting”.  Hormonal influences are a powerful force which has insured the survival of the species:  boys and girls will get together.  There are many plants that contain phytoestrogens, a hormone that can mimic the  effects of naturally occurring substances that can cause mammary development in non-pregnant mares.  Soybean products are a good source of these compounds, so check any grain or “supplements” for the presence of soy-based material.  An infection in the mammary gland called mastitis can also cause a milky discharge, so a vet exam would also be helpful to diagnose and treat this problem. Finally, there are some mares that present with a “milk-like” secretion for absolutely no apparent reason. This will not likely be treatable, but also not a real problem, so therapy would not be warranted.

Question: I have a 16-year-old maiden mare that has gas ulcers off and on. I have been treating her with omeprazole as she does very well with it and has been able to keep the episodes at bay for 3 ½ months. Unfortunately, it is now back and am looking to treat another round. I am considering breeding her in February. Should I be concerned? 

Answer: EGUS (gastric ulcers in horses) has been carefully studied over the recent decade, and  our understanding of this very common syndrome has changed.  Omeprazole, (prilosec, gastroguard, ulcergard) js one in a class of drugs called proton pump inhibitors (PPI).  Although it has long been considered safe, recent evidence has suggested this type of compound must be used with caution.  In mares, the recommendation is: “The safety of omeprazole in pregnant and lactating mares has not been determined. Do not use in pregnant or lactating horses unless benefits outweigh the risks. Avoid use in foals less than 4 weeks of age.”  In addition, horses experiencing multiple bouts of EGUS–even those that have responded to PPI’s in the past–may benefit from other management techniques with lower to no risk. Slow feeders and natural products that elevate gastric pH (Aloe Vera juice and some seaweed extracts) have been a quite effective part of EGUS management.

To make things just a bit more complicated, sixteen-year-old-maiden mares can be a challenge on several levels. Older mares, especially maidens over the age of thirteen or so, will commonly be difficult to impregnate, so you are going to need help. You should seriously consider starting artificial lighting now. Sixteen hours of darkness and eight hours of light (bright enough for her to read a newspaper in every corner of her stall) will stimulate most mares to produce a normal ovulation cycle by the first of February.  Your local AAEP veterinarian can guide you through this aspect of equine reproductive and nutritional management.