AAEP Ask the Vet: Preparing for Breeding Season

Preparing for the Breeding Season
  1.  1. There are so many things we are supposed to do to our mares 30 days prior to foaling (i.e., vaccines, deworming, etc.). What exactly is 30 days prior considering gestation is 320 to 365 days, since so many horse owners go by all sorts of calendars predicting foaling anywhere from 327 days to 343 days?2. Is HCG a viable option to help stallion fertility?3. All male mammals have nipples, where are they located on male horses?4. At what age do mares eggs start to go bad, for example in humans women over age 40 are more likely to have a child with birth defects? 

    1. The last trimester of a mare's gestation is an important period for the final maturation of the fetus. In addition, the mare's body is busy preparing for a successful delivery and lactation. It is generally recommended to schedule the mare's routine vaccinations during the period that falls 4-6 weeks prior to the due date. The normal gestational length of the mare can vary quite a bit, but the average length is 340 days from ovulation. Knowing the prior reproductive history of an individual mare can be helpful; mares tend to have similar gestational lengths from one year to the next. If the history is unknown or if the mare is a maiden, then plan to administer her pre-foaling vaccines six weeks prior to the due date. This will give her adequate time to mount an immune response and have good levels of antibodies in her colostrum that will be protective for the newborn foal.

    2. Subfertility in the stallion can be a very frustrating problem to tackle. There are a myriad of causes of subfertility. Administration of  HCG (human chorionic gonadotropin) to a stallion is useful in determining if the horse's reproductive problems have a hormonal basis. However, treatment with HCG injections has not been shown to improve fertility in the male horse.

    3. This is the most entertaining question of the month! Male horses do indeed have nipples. They are quite rudimentary, and often difficult to see. They are located on the underside of the horse's sheath. It can be nearly impossible to see them in a standing horse, but the next time you have the opportunity to observe a castration of a young colt, you may see them while he is in dorsal recumbency.

    4. It is well documented that ageing has a negative effect on fertility in women. This also holds true for the mare, although the topic is not as well-studied in horses. A mare's fertility begins to decline in her mid-teens. Many factors are to blame for the age-related decline in fertility, but oocyte (egg) quality is ultimately the primary reason. Studies in mares show that oocyte quality is significantly decreased in mares over 19-20 years old. "Birth defects" due to chromosomal abnormalities are not as recognized in older mares as they are in older women. Dr. Kerry Beckman, Prospect, KY

    1.  How often should a stallion's sheath be cleaned during the breeding season? 

      Cleaning a stallion's sheath during breeding season is an important part of proper management. The horse should be teased so that he achieves an erection, and washed with warm water. Do not use soaps or disinfectants. If the stallion typically takes several minutes between washing and mounting, then drying the penis is not necessary. If he usually mounts immediately after washing, then blotting the penis with a clean paper towel will be sufficient to remove water that could negatively affect semen quality. 

      If it is safe to do so, a stallion should be cleaned prior to each breeding, whether it be natural service or semen collection. If the stallion is bred multiple times per day, cleaning him before the first "jump" is usually sufficient for that day. If he is used for live cover, he should also be rinsed off after mating, to reduce the chances of transmitting infection. There is usually no need to clean the stallion's genitals between breeding episodes, even if he does not breed frequently. Frequent washing (even using only warm water), removes the normal micro-organisms that reside on the sheath and penis, which predisposes him to an infection from more potent bacteria. A study has shown that breeding stallions actually have more bacteria on their reproductive parts at the end of the breeding season, most likely due to repeatedly removing the normal flora.

      In summary, a stallion should only be washed when necessary for hygienic natural cover or collection of semen. A normal amount of smegma and bacteria are part of healthy external genitalia. Dr. Kerry Beckman, Prospect, KY

      1.  I own a 22-year-old Warm blood mare She had a live birth in 1996. She is in good health. Can I successfully breed her? 

        You ask a very interesting question, which does not have a straightforward "yes" or "no" answer. There are several factors to consider when breeding the older mare. Many broodmares can successfully produce foals into their mid-twenties. You must take into consideration the overall health of the mare. Conditions such as chronic laminitis, Equine Metabolic Syndrome, Cushings disease, and even chronic lameness can negatively affect the odds that the mare will conceive and carry a foal to term. The mare's reproductive history can also help predict her future breeding success. An aged mare that has carried a foal to term recently has a better chance of becoming pregnant than a mare that has remained barren. Older mares typically have a lower conception rate per cycle (i.e. 30-40%) versus their younger counterparts (that typically have a 60-70% per cycle conception rate). This means that you may need to breed your older mare several times in a season in order for her to conceive. Aged mares are more likely to have reproductive conformation problems than younger mares.  As the mare ages, her reproductive tract slowly succumbs to the effects of gravity, and sinks lower into her abdomen. Also, she may develop tilted vulvar conformation, or have an accumulation of urine in her vagina. All of these anatomic challenges will predispose her to a uterine infection.  Beyond the conformation of the reproductive tract, we also have to consider what is occurring on a microscopic level within the uterus. Older mares can often have scar tissue, cysts, and inflammatory cells within the lining of the uterus, which will make it more difficult or even impossible for her to produce a live foal. 

        The crucial first step to determine whether or not you should attempt to breed your older mare is to have a general health exam and a  "breeding soundness exam" performed by a veterinarian who specializes in equine reproduction. This will include a rectal palpation and ultrasound exam, a vaginal and cervical exam, a uterine culture and cytology, and a uterine biopsy. Other tests may be deemed necessary as well. Some clients are hesitant to spend the money on a thorough initial examination, but it will almost always save you money in the long run. A breeding soundness exam will help determine the odds that your mare can become pregnant and carry the foal to term. This will also help your veterinarian know how to best manage the mare before, during, and after insemination.  

        It is important to ensure that the stallion you choose is fertile, and has had his own breeding soundness exam performed recently. Live cover and artificial insemination with fresh, cooled semen are preferable. Breeding with frozen semen typically will further decrease the per-cycle conception rate, and is more inflammatory to the uterus than using fresh semen.  

        When managing the breeding cycle in an older mare, I believe that "an ounce of prevention is worth a pound of cure." This means that I tend to be very proactive in trying to minimize inflammation and infection that will occur with insemination. The mare needs to have a clean uterine culture and cytology prior to breeding. I try to manage the breeding cycle so that the mare is only bred once, and as close to ovulation as possible. Often, we assist the older mare in clearing the uterine debris and inflammation by lavaging (rinsing out) her uterus 4-8 hours post breeding. Daily ultrasound examinations will help determine the optimal treatment course. If the mare does conceive, the pregnancy should be monitored carefully to ensure the health of the mother and fetus.

        Perhaps the mare in question is valuable for genetic or sentimental reasons, but is a poor candidate to carry her foal to term. Advanced reproduction techniques can be used to successfully produce a foal. "Embryo transfer" is the most commonly employed technique, wherein the mare is inseminated, and the resultant embryo is removed from her uterus 6-8 days after ovulation and transferred to a recipient ("surrogate") mare for gestation. This technique has been very successful for obtaining foals from older mares, but does require that the mare have the ability to conceive and maintain a pregnancy for about a week. If the mare's reproductive tract is unable to accomplish this, then "oocyte transfer" can be utilized. In this procedure, an unfertilized egg is taken from the mare's ovary, fertilized, and placed in a recipient mare for the remainder of gestation. This technique is also fairly successful, but will incur higher veterinary costs.  

        In conclusion, there are many factors to consider when deciding to breed an older mare. A thorough examination by a veterinarian that is proficient in equine reproduction will help determine your chances of success. Typically, breeding an aged mare will require a higher monetary investment in order to obtain a foal, but can be well worth the time and effort. Dr. Kerry Beckman, Prospect, KY