Q3) Is it possible to control a mare's cycle, can I
decide when she will ovulate?
Yes, there are several ways to not only bring your mare into heat earlier in
the season but also to control when she will ovulate. There are basically two
methods, one is through the use of environmental stimuli and the other is
through the use of hormonal drugs and implants. Although there are arguments
against both by those who feel it is important to let nature run its course,
many breeders have found that by using one or both methods their breeding
productivity can be noticeably increased. And since there have not been any
recorded negative side effects to either mare or foal these methods are fast
becoming more and more popular.
In the wild, mares usually do not become truly fertile until May or June.
This is when the conditions are ideal because food is in good supply and the
longer daylight hours provide for increased activity and movement. This is a time
when horses can use their energy for other things rather than survival, which is
their main focus during the winter months. Breeding at this time also insures
that foals will be born in mild weather the following year.
If we can trick the
mare's body into believing that May/June has arrived in the middle of February
we will have access to her optimum fertility much earlier in the year. As
mentioned before we can achieve this through environmental stimuli. This
includes installing lights in her stall that will come on in the morning to
simulate an earlier dawn and stay on longer at night to simulate a later sunset.
The mare's feed can also be cut back severely in November and then slowly increased
early in the year, this simulates the "starvation" of winter being replaced
by the "bounty" of late spring.
Controlling when the mare actually ovulates can be much trickier process and
normally includes using hormone stimulators. One of these hormone stimulators is
called Ovuplant. It is a small implant that can be inserted under the skin and
releases a chemical called deslorelin which then stimulates the mare's hormones to
induce ovulation. Within 48 hours of the implant the mare should ovulate.
Although it seems like a great idea there is a catch. The American Association
of Equine Practitioners has announced that there was a significant percentage of
mares who had received Ovuplant inserts but did not conceive on the ensuing
ovulation that were not able to conceive for the rest of the season. For this
reason it has been suggested that if an Ovuplant is used that it is removed
immediately after it is determined that the mare did not conceive.
Another option is an injection of a hormone called Human Chorionic
Gonadotropin that will stimulate a mature follicle to ovulate in 24 to 48 hours
with an average of 36 hours. HCG is a hormone produced in the human body by the
placenta of a pregnant woman. It is present in the urine and is what causes a
pregnancy test to show a positive result. Normally the injection is given on the
same day as insemination or live cover. An alternative method is to
inseminate/cover the mare, then give the HCG injection, followed by another
insemination/cover 12 hours later.
Other hormones used to manipulate the mare's estrous cycle but not
necessarily to induce an ovulation are prostaglandin, progesterone and estrogen.
For example prostaglandin can be used to shorten a mare's estrous cycle. Or
perhaps you have 2 mares that need to be inseminated using a single
ejaculate. By using progesterone, estrogen and HCG it is possible to
synchronize both mare's ovulation to within just a couple of days of one
another. Alternatively, progesterone can also be used to prevent the loss of a
pregnancy and estrogen can be used to delay ovulation in the foal heat. This ability to restrict ovulation to a relatively predictable window of time has allowed many breeders to have more
successful conception rates.