Breeding Basics

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By Brandi Holohan, DVM, Pilchuck Veterinary Hospital

Before you take on the endeavor of breeding, you should equip yourself with some basic knowledge that will help in the decision-making process.  

Mares are in their reproductive prime from ages 6 to 8. A mare is considered aged after age 15. Cycling is most reliable between April and July without any other intervention. The mare’s heat cycle (from ovulation to ovulation) is approximately 18 to 25 days in length. It will tend to be longer early in the spring and shorter later in the summer. The mare will show heat for four to seven days, ovulate, and then be out of heat for 14 to 18 days. 
The mare should be up to date on vaccinations and dental health care prior to starting the breeding process. It is recommended that all mares have a pre-breeding exam. This exam should be performed while the mare is showing heat to allow for detection of any problems that could diminish her ability to become pregnant, carry the pregnancy successfully to term, or nurse the foal. This exam may be limited to a physical exam, rectal palpation and ultrasound, and speculum exam of the caudal reproductive tract. This allows for evaluation of all components of the reproductive tract and the mare’s overall health. 
Other routine diagnostics may be employed depending on the reproductive history of the mare. For example, a uterine culture and cytology would be indicated if there is any history of infertility or uterine fluid. Occasionally, breeding contracts require a mare to have this test performed and shown to be negative/clean prior to the stallion owner shipping any semen. Uterine biopsies may also be indicated if a mare has had reproductive difficulties, such as inability to conceive, pregnancy loss, uterine fluid retention or placental abnormalities. This would give information about the likelihood of the mare being able to conceive and carry a pregnancy successfully to term. If any issues show themselves, remember that an ounce of prevention is worth a pound of cure. Doing diagnostics early may prove to be more financially appropriate than waiting until later when time and foals are lost.  
If the mare passes her exam, it is time to focus on the stallion. Picking a stallion can be based on performance history, physical attributes or personality. It then becomes important to make decisions based on fertility. Questions to ask the stallion owner include: 
  1. What is the first cycle conception rate? This tells us how many mares got pregnant on the first breeding. 
  2. What is the season conception rate? This tells us the overall pregnancy rate, i.e., how many mares out of the total bred got pregnant.
  3. What is the average number of cycles per conception? A stallion may have an average of 1.4 cycles per conception or an average of three cycles per conception, but still have a 90+% seasonal conception rate. This makes a difference in your budget; if you have a healthy fertile mare, does she get pregnant on the first or second try, or the third or fourth try? You may need to put double the money into breeding the mare to achieve a pregnancy despite the stallion having a good seasonal pregnancy rate. 
All these numbers will change depending on the method of insemination undertaken: live cover, shipped/cooled semen, or frozen semen. All these methods have a different financial investment associated with them. This is important to consider when deciding on a stallion and method of breeding. 


Since 1996, the Equine Reproduction Center at Pilchuck has provided routine and advanced mare and stallion services. Please call 360.568.3111 for more information.

Mare and foal photos kindly provided by PVH client Adena Ray. This article appears in the January 2014 issue of the Washington State Quarter Horse Association newsletter.
Article added December 18, 2013