According to figures released by The Jockey Club last month, 33,746 Thoroughbred broodmares visited stallions this past breeding season. With an average gestation of roughly 11 ½ months, it's not uncommon for mares to take several foals before they produce their best offspring, which could have them in production for years. A quick scan of recent Kentucky Broodmares of the Year reinforces this notion: Dear Birdie delivered eventual classic winner Birdstone when she was 14 years old. Somethingroyal was 18 when she had Secretariat, and Better Than Honour was 17 when she foaled Jazil (Rags To Riches came along the following year).
But how should a manager make the tough (and sometimes financially-fraught) call to pension a broodmare?
There are no hard and fast rules regarding the broodmare's age, according to Dr. Tamara Dobbie, director of the Hofmann Center for Animal Reproduction at the University of Pennsylvania's New Bolton Center. There are a few things to consider when looking at the individual in front of you.
The first and most obvious is the likelihood of the mare to successfully get in foal. Dobbie sees some mares who experience fertility problems in their early teens, and others who remain reliably productive until their early twenties. A better predictor seems to be when the mare first went into production, and how consistently she produced foals. Dobbie has found mares who began breeding in their mid-teens are more likely to encounter problems than those who start earlier.
“We often recommend that older broodmares continue to carry pregnancies yearly or every other year until the mare is retired,” said Dobbie. “Broodmares that are given several 'years off' in their late teens can be very challenging to get back in foal.
An older mare could be more likely to develop health conditions of her own that could complicate carrying a foal. Metabolic syndrome and Cushing's disease become more likely as a horse ages, and both can impact fertility. Even without those problems, older horses generally tend to have more difficulty maintaining an appropriate weight, particularly in fall and winter.
“In older mares, paying attention to basic things like body condition score is very important,” said Dobbie. “Older mares often require adjustments to feeding, as well as more attention to their teeth in order to maintain a good body condition score. Mares in poor body condition are much more prone to problems with vulvar conformation that can predispose them to windsucking and subsequent uterine irritation or even infection.
“If a mare does get pregnant in spike of windsucking, problems can still occur during gestation. For example, mares with poor vulvar conformation are much more prone to placentitis during pregnancy.”
Dobbie doesn't want to see mares become obese, but overly thin horses may be more difficult to get in foal. Additionally, they may not be able to meet the metabolic demands that go along with nursing a growing foal. Milk production can drop off and this can affect the foal's wellbeing. A body condition score around 5 on the Henneke scale is appropriate, and feed adjustments may be needed to maintain this score. Basic veterinary care, including regular dental check-ups and dewormings are important in helping mares, particularly older ones, maintain weight during pregnancy and while nursing a foal.
A mare's soundness should be a concern for breeders, also. If she was retired due to unsoundness, owners need to question whether the horse can remain physically stable along with the added weight of pregnancy.
Although the notion of carrying and delivering a baby every year sounds daunting to humans, Dobbie isn't convinced all mares experience acute 'wear and tear' on their reproductive tracts after just a few foals. In some older, veteran broodmares however, she does see a loss of uterine tone and this often makes it more challenging for the mare to clear fluid and prevent infection after breeding. For the most part, Dobbie said, difficulty conceiving doesn't equal difficulty delivering foals, so older horses aren't inherently prone to danger at foaling time.
Instead, the decision to pension a mare often comes down to the ease of getting her in foal again. During a breeding soundness exam, Dobbie will often take a uterine biopsy and rate the tissue on a scale of 1 to 3, with a 3 giving the mare the poorest chance of carrying a pregnancy to term. When fibrosis or other factors result in a score of 3, she advises clients against breeding the mare if the horse is expected to deliver the live foal herself.
Although fibrosis is often associated with aging, some mares develop significant fibrosis even at a relatively early age. In Dobbie's experience, other much older mares sometimes present with almost no fibrosis.
When it comes to weighing risks surrounding delivery, Dobbie is more concerned with a mare's history (especially one that includes uterine artery bleeds or dystocia) than age.
“Once a mare has had a foaling problem, you want to be extra vigilant during subsequent foalings,” said Dobbie. “It is often a good idea to have these mares foal at a facility where assistance can be provided immediately if the mare experiences trouble. We can also see problems in mares with no prior history of foaling difficulties. Because of the possibility of unexpected problems, it is very important that foaling be attended, even when the pregnancy appears to be progressing normally.”
“A lot of mares who have these problems might not have ever had a problem before.,” she said. “A mare could have a uterine artery bleed in the broad ligament when she's 12 or when she's 20. We used to think uterine artery bleeds occur more frequently in older mares, but the research doesn't support that.”
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