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Transitional heat cycles

By Jim Dettmer

Many mare owners are confronted with an idealistic idea of breeding for that January baby. That can be a difficult proposition because it is not naturally what a mare wants to do. It does not make sense to the mare to have a foal in the coldest month of the year. Naturally speaking, the survival rate for a foal that is born in January is very low, which is why a mare will wait until later in the spring to come in heat.

Fortunately, we can be a little savvier in our breeding practices to get us breeding earlier in the season. It should come as no surprise to most breeders that a mare’s cycles can be manipulated by putting them under artificial lighting. While there is some debate over which technique is most effective, you should find something that works best for you and do it consistently. If it is not consistent, it will undoubtedly be ineffective. I personally have a timer that I picked up from the hardware store, and it works quite well. Expect another article at another time that goes further into depth on manipulation of heat cycles. In the mean time, take a moment or two to find out about artificial lighting and how to use it to bring your mare in earlier.

One thing that is often not talked about when breeding mares early is that they will “cycle” before they are ready to be bred. There is almost always a transitional heat cycle when a mare is transitioning from anestrous in the winter months to being the Fertile Myrtle mares we all know and love in the spring and summer months. During that transitional heat cycle, the mare will come into heat, but will not produce a viable follicle.

The follicle contains the egg and grows, becomes irregular in shape and breaks open. When the follicle breaks open, the egg is released and, (God willing), meets up with a member of your favorite stallion’s swim team to be fertilized. This process is called ovulation and fertilization. Hopefully you have timed your semen shipment or cover date to correctly coincide with this magical moment.

The heartbreaker of the deal is when we try to get that mare in foal as early as we can. If that mare isn’t producing a viable follicle, she isn’t really ovulating. The bottom line: no egg, no pregnancy. It is very frustrating for mare owners and it can also be very expensive to have your vet out to ultrasound all the time. And an overzealous vet may have you order semen that will have as likely a chance of getting your sink drain pregnant as it would your mare. To further compound the problem, I have seen mares that build a follicle, and then begin to reabsorb it without ovulating during a transitional cycle.

Please also know that Prostin and similar products will not make a mare that is in anestrous come into a true estrus heat. It is not a magic shot that will bring them in whenever you want. There are appropriate ways to use it and there are techniques that just won’t work. Talk to your vet and see what options are best for you.

Don’t get mad. It’s not your mare’s fault! Or your vet’s fault. Or the stallion owner’s fault. If you need someone to blame, go ahead and blame Mother Nature and Father Time.

The best way to insure a mare is not transitional is to ultrasound. But be smart about it. If you watch your mare, and you believe that it is her first heat cycle, it is unlikely to be a true heat cycle and she is probably transitional. If her heat goes on for a while, or is hot and cold, you might want to hold off. A tease stallion is a great way to check up on your mare to see how she is doing. Having her on the farm with your favorite stallion is even better.

After seven days of her being in a heat cycle you suspect is transitional, you can start her on Regumate for 15-18 days. At the end of the Regumate cycle, give her a shot of prostaglandin and watch for the fireworks.

If you using shipped semen, you are hopefully having a vet help you with an ultrasound to tell you the size of the follicle and how soon she will (probably) be ovulating. Knowing your mare and what size follicle she usually ovulates at will be very helpful at this time.

The bottom line is, you will find yourself in a much better place if you know where you mare is at. Manipulating what Mother Nature intended is a difficult proposition, and sometimes waiting will help you find a lot more success with a lot less frustration. Just make sure you trust your veterinarian, and even if you do, be educated enough to make the right decisions for your situation and your mare.

Request for reprint must be directed to Jim Dettmer