BY

Official Wellness Partner of the NRCHA

Mare reproductive wellness begins and ends with nutrition.

Mares are seasonally polyestrus, meaning they naturally cycle several times during certain seasons of the year. Since pregnancy in a horse lasts about 11 months, five days, they were designed to foal when the grass is green and the days are warm. To accomplish this goal of foaling when the days are warm and long, mares must breed back quickly after foaling. This means they must cycle.

The reason mares are designed to foal in the late spring and early summer is because they will have plenty of grass or nutrition to produce milk and maintain body weight. A mare’s body weight is the No. 1 factor in my opinion in determining how well a mare cycles.

Mares are supposed to cycle every 21 days. There are many things that throw them off course. They are designed to cycle when the days are their longest. That is around the summer solstice the third week of June. You can move cycling up in the calendar by placing mares under artificial lighting—16 hours of light stimulate the pineal gland in a mare’s brain to wake up her reproductive organs. If it’s the right time of year, such as when the days are long, nutrition or the lack of it will disrupt a mare’s ability to cycle correctly.

Transitional estrus or “transition” is when the mare’s reproductive cycle is erratic. She may build follicles and regress them. She might short cycle herself or have prolonged estrus where she builds a follicle and won’t ovulate it.

Mares cycle the best when they are gaining weight. Conversely, they cycle the worst when they are losing weight. A skinny, dry mare on poor nutrition and not gaining weight is not going to cycle correctly even if the days are long. The same is to be said of the post-foaling mare that’s milking hard. If she’s receiving poor nutrition, she’ll use all her energy to make milk and feed her foal. Nothing will be left to give her energy to cycle back.

The perfect body score or body condition for a brood mare to cycle from a practical standpoint is when you can feel their ribs but not see them. I don’t like them too fat or too skinny. Fat mares don’t cycle well either.

I’m comfortable with a dry mare being a little thin in October and November. This body condition allows her body to shut down, so to speak, when the days are getting shorter and losing a little weight is a good strategy. This is followed with artificial lighting beginning December 1 and increased nutrition if your goal is to breed by or on February 15. If your mares put on 75 to 100 pounds between December 1 and February 15, and are getting 16 hours of bright light a day, I can almost guarantee they will be cycling.

However, you can’t use the same strategy with pregnant mares. They need solid nutrition and stable weight the entire pregnancy. The last trimester is the most important because all the micronutrients the foal needs are delivered to it during this period. The most important thing to help post-foaling mares cycle back is to at least maintain and not lose body weight. They need to turn into eating machines, especially if they are heavy milkers.

Reproductive wellness and cycling begin and end with nutrition. You can have a mare under lights, but if she isn’t gaining weight, or worse losing weight, she won’t cycle very well. If you have any questions, contact your local veterinarian.

Joe Carter, DVM Oklahoma Equine Hospital Official NRCHA Veterinarian

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