February 11, 2011
The older broodmare presents some challenges during breeding season.
By Dr. Patrick McCue in The American Quarter Horse Journal
Older mares can become pregnant and carry foals to term into their 20s. One of the oldest mares recorded to give birth was a 42-year-old mare in Australia. However, the overall reproductive potential of a mare typically begins to decline by about 15 years of age. Pregnancy rate per cycle and seasonal foaling rate both decrease with age.
Owners need to understand the inevitable age-related changes in mares and develop realistic expectations regarding breeding potential. Assisted reproduction techniques such as embryo transfer and oocyte transfer have allowed many mares to continue to produce offspring well beyond their normal reproductive life span. Let’s review ovarian problems that develop or increase in frequency with advancing age in broodmares.
So, you’re ready to breed your mare. What steps do you need to take to breed her at home with shipped semen? In AQHA’s FREE Mare Care Report, Dr. Racqhel Rodeheaver of Fort Collins, Colorado, explains the process of preparing your mare, targeting a breeding date, ordering semen, inducing a follicle to ovulate, receiving and evaluating semen and much more.
One of the first changes an owner might notice is a delay in the first ovulation of the year in older mares. On average, older mares ovulate about two weeks later in the spring than younger mares. The interval between cycles during the breeding season is four to five days longer in older mares as well, primarily due to a slower growth rate of developing follicles.
Mares over 20 years of age can experience irregular estrous cycles, and it is not unusual for mares over 25 to stop cycling altogether. The phrase that has been used for this phenomenon is ovarian senescence.
The incidence of ovulation failure increases with age. In young mares, failure of the dominant follicle to ovulate occurs in less than 5 percent of cycles. In contrast, up to 13 percent of estrous cycles in mares 15 years old or greater result in ovulation failure. This issue alone can make breeding management of older mares unpredictable, frustrating and expensive.
It is common practice to induce ovulation in mares in heat with human chorionic gonadotropin (hCG) or deslorelin, a potent derivative of gonadotropin-releasing hormone. The effectiveness and predictability of hCG and deslorelin decrease slightly with the mare’s age.
The oocytes or eggs in the ovaries can also be adversely affected by age-related changes. A mare is born with all the oocyctes she is ever going to have. This is in sharp contrast to the situation in stallions, in which new sperm are produced throughout the reproductive life of the male. Oocytes must be penetrated by a sperm (or fertilized) within 12 hours after ovulation. Conflicting data exists regarding fertilization rates in older mares. Some studies have reported that fertilization rates were similar between older mares and younger mares, while other studies noted lower fertilization rates in older mares.
There is little dispute about the fact that pregnancy rates in older mares are lower than those of younger mares and that older mares have a higher incidence of pregnancy loss. The difference in pregnancy rates and embryonic loss rates might be due to defects in the oocyte, changes in the oviductal or uterine environment, or other factors.
Learn the steps for broodmare preparation and get the facts on receiving shipped semen in AQHA’s FREE Mare Care Report. For instance, did you know that you should never leave a semen shipping container in the sun? Read this report to learn more.
Age-related alterations in reproductive functions most often occur slowly and progressively. A reduction in fertility is a natural and predictable course of events as a mare ages. Recognition of potential problems and adjustments in management procedures can often result in a successful breeding program with older mares. Attention to detail, maintenance of sound medical and nutritional programs and selection of fertile stallions are just a few of the keys to success.
Opinions abound as to the best breeding strategy for older mares. One generally accepted principle is that older mares that have recently carried a foal to term are easier to breed back than similarly aged mares that have been intentionally left open for a year or two. A second universally accepted principle is that older maiden mares are notoriously difficult to get in foal.
Please consult with your American Association of Equine Practitioners veterinarian for the optimal breeding management options and techniques for your older mare.