There are many reasons to short cycle your mare. You may be breeding around her show schedule, coordinating your calendar around the stallion’s or recipient mare’s availability, your veterinarian’s schedule or even synchronizing with other mares at the farm.
Short cycling simply means shortening a particular phase in your mare’s cycle. In the most simplistic terms, mares generally complete a full cycle every 21 days. Day one is ovulation, with 4-6 days of heat (estrus). If she’s not pregnant, estrus is followed by diestrus, non-heat, in which her body once again prepares for ovulation.
It’s during the 14-16 days of the luteal phase of diestrus that your veterinarian can administer prostaglandin to shorten your mare’s cycle. In the luteal phase, your mare develops a corpus luteum (CL), which produces the hormone progesterone that suppresses estrus. When prostaglandin is administered, the CL begins to break down causing progesterone to drop and allowing the mare to come into heat. Most mare will enter estrus within three to four days and ovulate within seven to 10 days.
Your mare is a candidate for short cycling if she cycles regularly and has recently has produced a large follicle. Never administer prostaglandin to mare without first having an ultrasound to ensure that she’s not pregnant and that she has a CL. Your veterinarian will also assess the size of her follicle. If she has a 35mm or larger follicle your mare may come into heat very quickly and ovulate within two or three days.
Andrea Bomkamp, broodmare manager at Iron Spring Farm, shares her tips for mare owners short cycling their mare for the first time.
How should you prepare your mare for short cycling?
Andrea: Your veterinarian will ultrasound your mare to make sure she has a mature CL. Prostaglandins aren’t effective if given at the wrong time of an estrus cycle. If you’re breeding your mare with cooled sem*n, the stallion owner may ask for an estimated date so they have an idea of when their stallion may need to be collected.
What kind of data should mare owners keep to help their veterinarian coordinate the process?
Andrea: Be sure to keep track of when your mare was last showing signs of heat. Recording the results of your mare’s reproductive ultrasounds will help you track of the length of her heat cycles and the size of her follicles when she ovulates.
What should mare owners new to short cycling ask their veterinarian?
Andrea: Be sure to to ask which medication your mare will receive and any side effects you should be aware of. There are two main medications used to short cycle mares. One of them can cause sweating and cramping, which can be quite alarming if you are not prepared. Another good question to ask is, how soon after administration should you anticipate your mare being bred?
Which mares are not candidates for short cycling?
Andrea: Pregnant mares! Prostaglandin will destroy an embryo that has formed in a mare’s uterus. Although, it can used to abort unwanted pregnancies (up to a certain gestation time).
Is there a limit to how many times you can short cycle a mare in a single season if she doesn't get pregnant the first time?
Andrea: Every mare is different, but it is nice to let her cycle on her own every now and again if you are having trouble getting her pregnant or retrieving functional embryos.
What is the best day of the week to give prostaglandin to avoid your mare ovulating on Mondays and therefore requiring weekend shipping for sem*n?
Andrea: Wednesday or Thursday are probably the best days to give prostaglandin to avoid weekend breeding. Be sure to check your mare on Sunday in case you need to order sem*n Monday for a Tuesday breeding.
However, knowing your mare is very important in this situation. Some mares may ovulate four to five days after prostaglandin. So if you give prostaglandin Wednesday or Thursday, she may ovulate before Tuesday when the sem*n arrives. This mare would be better managed with a Sunday or Monday prostaglandin so you are more likely to receive cooled sem*n in time. Work closely with your veterinarian to assess the best days for scheduling prostaglandin.
Anything else you think people should know about short cycling?
Andrea: Not every mare reads the text book. Your mare may ovulate earlier or later than normal even with medication.
Work with your veterinarian to learn more about short cycling your mare and breeding the foal of your dreams. Learn more about scheduling shipping here.
All content provided by Iron Spring Farm is general and for informational purposes only. Content may also not constitute the most up to date information. Nothing in this content is intended to constitute veterinarian advice or to serve as a substitute for consultation with a veterinarian. Always seek the advice of your veterinarian or other qualified provider with any questions that you may have about the treatment and care of your horse. Any reliance that you place on the information provided is strictly at your own risk and Iron Spring Farm, its officers, employees, representatives, and agents, hereby disclaim any and all liability to any party for any direct, indirect, implied, punitive, special, incidental, consequential or other damages arising directly or indirectly from access to or use of any content provided to the maximum extent permitted by law.
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