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
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
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
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.