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Stimulating Mares to Cycle Early
Stimulating Mares to Cycle and Ovulate Early
Introduction
Depending upon the breed of horse and the goal of the breeder, foals born earlier in the year are often times more desirable. The reason for this is that several breeds, including the Thoroughbred, recognize January 1st as the first birthday of all the foals born the year before. This means that a foal born February 2nd is considered to be one year old at the same time as a foal born on June 27th. This gives the foal born earlier a potential advantage when the two are required to race or show against each other when young.
Therefore, our goal in many instances is to get the mare bred early in the year since their gestation period is about 343 days. This presents a problem because most mares go through a winter anestrus, during which they do not cycle, followed by a transitional phase, during which estrus and ovulation aren't always synchronized. Left to Mother Nature, most foals would be born in the late spring or early summer, as it takes until then for mares to be regularly cycling and ready for breeding.
In this article the specifics of artificial lighting, altrenogest (Regumate) and sulpiride to induce mares to cycle early in the year is discussed. Recent advances have greatly shortened the time required to get a mare to ovulate in the dead of the winter.
Artificial Lights
The following is an article wrtiten by Bill Ley DVM on the use of lights to stimulate mares to cycle and ovulate early.
Artificial Lights
One way in which we can manipulate a mare's ovarian activity is by the use of artificial lighting. In this way we can increase the possibility of having estrus accompanied by ovulation so that fertilization can occur earlier in the year. It takes about four to six weeks to stimulate the mare's ovaries out of anestrus and another four weeks to get through the transitional phase, so November 15th to December 15th is the best time to start the lighting program. The physiological premise behind this program is that extended daylight provides the main drive for estrous activity in mares. Although other variables such as temperature, and forage availability also play a role, length of daylight plays a greater part.
It has been determined that 15 to 16 hours of daylight per day are required in order to stimulate the mare's brain appropriately. There are a couple of ways to do this. On your chosen starting date you can simply add the required amount of hours of light at the end of the day. Another way is to gradually build up to the required 15-16 hours by supplying an additional 30 minutes of light each week. Either way, it has been shown that the best way to add the extra light hours is at the end of the day and not in the morning. An electronic timer which you can purchase at a department or hardware store makes this an easy task, and is quite reliable.
The intensity of light needed to stimulate ovarian activity is 10 to 12 footcandles. In a 12'x12' box stall, a 200 watt incandescent bulb or two 40 watt fluorescent tubes should be placed seven to 8 feet above the stall. Large groups of mares have successfully been stimulated to cycle using large metal halide lights affixed above a paddock. Within 40 to 70 days your mare should be cycling and breeding can be started.
How Light Stimulates Estrus in Horses
Although it is not fully understood how this works biologically, we do know that light suppresses the pineal gland's (in the horse's brain) secretion of melatonin, a hormone important in carrying messages about daylight length to the brain's estrous cycle control center.
So get ready--all you need is a few light bulbs and an electronic timer and you too can have an early-born foal, and a jump on the breeding season.
Regumate is an Important Adjunct to Early Ovulation
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