Breeding and Reproduction

Breeding and Reproduction

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Have you been curious about breeding your mare? Sweet River Equine Clinic, Inc. has a wonderful breeding program and we are excited to share it with you! We will discuss Artificial Insemination (AI), fresh semen, fresh cooled semen, frozen semen and embryo transfers. This is going to help you decide which is the best route for you and your mare.

Artificial Insemination (AI) is using an alternate method to breed horses by using fresh, fresh cooled, or frozen semen. The first successful record of AI was in 1780 by an Italian scientist, Lazzaro Spallanzani, bred a dog with freshly collected semen and later delivered a small litter of puppies. Spallanzani did it again in 1803 when he placed dog semen in the snow and recorded it becoming motionless. He then warmed it to notice it became mobile once again. The desire to make a broader use of better sires made AI advance to what we do today.

It is important to coordinate semen shipments with the mare’s ovulation when using cooled semen. When the mare is in heat she will need to be checked daily and bred within 24 hours of her ovulation. A mare bred within the 24 hours before ovulation has the highest pregnancy rate. An important aspect to remember when breeding your mare is the quality of the semen. Stallions with low fertility may have much lower conception rates than those with high inherent fertility. If needed ovulation can be induced using an ovulatory inducing agent called Deslorelin (which is what we use here at Sweet River Equine Clinic, Inc.). Ovulation with Deslorelin can occur as early as 24 hours or as late as 48 hours. After insemination, the mare should be checked daily until she ovulates. If she does not ovulate within the 24-hour period she should be inseminated a second time.

The advantages to using cooled semen, and the costs incurred with breeding your mare with cooled semen. The best advantage of using cooled semen, is that the location of the stallion is of little consequence. There is no need to endanger the mare and foal with a shipping method. Having a broader spectrum for choosing the ideal stallion based on pedigree or performance traits is a great reason to use cooled semen. Costs that can be associated when using cooled semen can include collection cost, semen extenders and shipping costs. Other costs can include teasing the mare. And, don’t forget your vet! Veterinary costs can include palpitations, ultrasounds, exams, pharmaceuticals, and the actual breeding, as well as, board and feed if the mare is staying at a veterinary facility. When considering breeding your mare with cooled semen, make sure to keep all of these in mind. Also, make sure to check with your breed registry, because there may be restrictions when using cooled semen.

Planning and prep for the mare, because planning and preparation are key to a successful pregnancy with cooled shipped semen. Some facts that have been presented in previous posts are so important we may be repeating them here for your knowledge and guidance. Having a fertile mare is the start of a good pregnancy experience with cooled shipped semen. The mare should be in good health with a regular cycle. She should be bred as close to ovulation as possible. Palpating the mare daily, once in heat, ensures the most accurate, as can be, timing for insemination. An HCG shot will be given once the follicle reaches 35mm in diameter, and semen will be ordered. The HCG shot is a fertility shot used to aid the mare in ovulating within 36 to 48 hours. Semen selected to breed the mare should be ordered as soon as the HCG shot is given. The veterinarian will then inseminate the mare once the semen has been received. Depending on how many doses have been sent, and the mares ovulation cycle, she can be inseminated again the following day. After insemination the Veterinarian will use an ultrasound machine to check if the mare has ovulated; after ovulation the mare is sent home. The Veterinarian should recheck the mare as early as 15 days to see if she is pregnant. At 30, 45, and 60 days the Veterinarian should be rechecking the pregnancy. If the pregnancy took you should see your new foal in 11 months 3 weeks and 3 days.

The Stallion. Keep in mind, when choosing your stallion, not every stallion produces the same quality and quantity of semen. There are extenders, but they may not work equally as well on every stallion. Veterinarians with successful experience using extenders is best when it comes to a successful pregnancy. Semen extenders are important to add so the viable semen will amount to 25 to 50 million cells per cc. 500 million cells is the number of sperm necessary for an acceptable pregnancy. When shipped, at least 1 billion cells are sent in a volume of 20 to 150cc of extended semen. These calculations are not done at every collection, and if the semen quantity is more than 1 billion that is Okay. When semen is shipped, it is usually used immediately upon arrival for cooled semen. It does not need to be warmed and double insemination in the 24-hour window may not increase the probability of pregnancy. It is very important to choose the right resources for handling the semen. Make sure to contact your vet if you have any questions about the stallion or his semen before choosing him to inseminate your mare.

Frozen semen is handled differently, and different techniques are used when inseminating a mare. Owners that use frozen semen on mares may need to find out a few things before committing to frozen semen: cost, size and number of straws, does the veterinarian have nitrogen tanks to store the semen (yes, we do), and the paperwork that will be included for the breed registry. When using frozen semen mares will be examined every 24 hours while in heat until the follicle reaches 30 to 35 mm in diameter. After desired size is reached the mare is then given hCG or Ovuplant, and then ultrasound at 24, 30, and 36 hours. If the mare ovulates during those times, she should be inseminated immediately. Twelve hours after insemination the mare should be checked again, and continually checked until she inseminates again, at which time she will be inseminated a second time. Two inseminations should be effective for most mares. Also, some mares can develop an inflammatory reaction to the frozen semen, because with frozen semen there is no seminal plasma. If that happens, the veterinarian will perform a routine uterine lavage 12 hours after breeding to clear out any by-products.


Embryo transfers are great for horses that are showing and do not need to be removed from their primary use to have a foal. ET is also beneficial for mares that have a hard time caring a foal to term. Embryo Transfers can be helpful to increase the annual reproductive rate in specific mares. Embryo transfers can be pricey though, so keep in mind that if moth mare and stallion are fertile, the cost can range from $7500 and up. If an owner wants to break even, the foal needs to be worth at a minimum $10,000.

A mare has her embryo collected 8 days after she has ovulated. Proper veterinarian management is key to having a successful embryo transfer done. The mare needs to be palpated every 12 hours until ovulation after she is bred to accurately determine the time of ovulation. Embryos are collected by uterine lavage. The fluids are collected using a special tubing that is attached to a cup with very small holes to not let the embryo slip through. Once an embryo is found it is placed in a dish containing transfer media and washed multiple times. To place the embryo in the recipient mare, the veterinarian will put the embryo in an insemination gun that is inserted through the cervix and discharged into the uterus.

This is our last breeding post in this series. We hope you learned a lot about breeding your mare and the different methods that are available. It is important to do your homework before making a decision on breeding your mare.

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