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Vet's Corner

Breeding Older Mares

Reproductive efficiency in mares, as in most species, generally decreases with age. In Standardbreds, 15 years or greater, would fit the older mare category. A young normal mare has about a 60% chance of becoming pregnant at each estrus cycle(heat) if mated to a fertile stallion. Older mares only have about a 30% chance of becoming pregnant on any given estrus when mated to a fertile stallion. Older mares often need to be bred twice as many times as younger mares and frequently don't conceive year after year.

Now I know some of you are saying my 25 year old mare has had 10 foals in the last 10 years and yes there does appear to be some exceptionally fertile older mares. These mares are usually under excellent management and bred at the right times to very fertile stallions. With age, they are the exception not the rule.

Breeding the older mare in the race industry is usually based on the economic or sentimental value of the mare rather than the prognosis for fertility. Therefore they frequently present a challenge to the owner, the attending veterinarian(s), and the stallion owner.

Some general recommendations one can make on breeding older mares includes the following. Donít push them too much ó allow sufficient time after a previous foaling for her reproductive tract to get back to normal shape. I love foal heat breedings but with older mares that donít have all the criteria necessary for foal heat breedings, my records tell me that the failure rate is higher and early embryonic death(EED) rates are higher as well. In fact EED rates are significantly higher in older mares no matter what stage they are bred .Young mares have about a 10% chance of losing a pregnancy from the day of diagnosis to the expected foaling date, while older mares run in the 25-30% range. Such things as embryonic defects, chromosomal abnormalities, failure of embryonic implantation or transport due to uterine or tubular fibrosis(scarring) or inflammation are frequent causes in the older mare.

Proper nutrition and exercise are very important in older mares and particular attention should be paid to them prior to foaling and/or breeding. Poor physical condition(under or overweight) and chronic musculoskeletal problems in older mares makes their breeding prognosis even lower. Lameness problems are often important in former race mares as some of these problems like arthritic conditions, founder etc. become exaggerated when these mares are carrying foals.

If you are going to spend a lot of money on an older mare to get her in foal, e.g. high priced stud, long distance trucking and extended board rates, then I think it is important that you have a complete evaluation with your veterinarian and decide if this particular mare is a good candidate for what you want. I encounter it frequently ó the older mare that has been a great producer, no trouble at all 5 years past,and may or may not be barren now. What was in the past is not what is in the present and mares wear out just as we do. Let your common sense overrule your emotions.

An aged mare that has recently had a foal is much more likely to get in foal than a mare the same age that has been barren a year or more. Mares 18 years or older that have not had a foal for 2 or more years are almost impossible to get in foal because their reproductive tract atrophies or loses its function because it hasnít been used for a few years. On the same accord maiden older mares are also difficult to get in foal because their fertility is decreased.

Evaluations with your veterinarian should include the following. A complete assessment of the mares physical condition and her prior breeding history. A complete reproductive tract evaluation usually will yield some valuable information. Diagnostic techniques would include a rectal examination, a manual vaginal/cervical examination +/ó vaginoscopey, uterine cytology and culture, ultrasound exam, and ultimately, a uterine biopsy. I usually perform all of these with the exception of the vaginoscope exam unless adhesions are anticipated. Later, if the mare does get in foal, then evaluation of Estrone Sulfate and Progesterone levels helps in maintaining a pregnancy as older mares sometimes have hormonal abnormalities.

Results often suggest treatments which are usually beneficial. Older mares with poor perineal conformation should definitely have a caslicks performed (stitched up). Uterine cysts, uterine fibrosis, chronic low grade endometritis, or ovarian inactivity are some of the common reasons given for a poor prognosis to an owner.

Even if your older mare does get in foal and survives EED, there are still some increased risks latter in gestation which include rupturing the middle uterine artery which usually results in death, vaginal vein rupture is less severe but can cause hemorrhage problems, premature placental separation, and increasing the severity of existing musculoskeletal problems.

The ultimate goal of every breeder is one live foal per mare per year. Older mares certainly can achieve this goal, but owners must realize that the prognosis for fertility ,conception and delivery decreases on a yearly basis. The cost of trying to achieve that goal with older mares can get way out of line in a hurry and a proper evaluation at the right time can not only save many headaches but it can also correct many reproductive problems before you start, giving the mare a much better chance of success.