What constitutes an “old” mare in breeding terms, and what increased risks might a more senior mare face? Selene Scarsi investigates the challenges and advantages of breeding from older mares
One of the UK’s leading reproduction vets, James Crabtree, director of Equine Reproductive Services (UK), admits that “how old is too old?” is a question he is asked a lot when it comes to breeding from mares.
“The truth is, each mare is an individual; it also depends on the breed, as thoroughbred and warmblood types tend to age more than native ponies. But, generally speaking, a mare’s fertility starts to decline at around 14 to 15 years old,” he says.
The first thing to bear in mind is that breeding – carrying a pregnancy and delivering a foal – will always represent a risk, regardless of age.
“It’s the same with humans — just think back to Victorian times, when pregnancy was one of the leading killers of women,” continues James. “With older mares, the risk is increased, although it’s difficult to quantify this increase. For instance, they will be more susceptible to complications, such as a uterine bleed, as the arteries that can bleed do degenerate with age.
“With older mares we also have a few limiting factors. As with women over the age of 40, who see the chance of having a baby decrease significantly, a mare is also less likely to produce a pregnancy and carry it to term, because the genetic material in the egg gets older.
“If we look at conception rates per cycle, younger mares (aged two to 11) will be on 57%, but with older mares (over the age of 14) this goes down to 31%. The foaling rates per breeding season (which might include multiple breeding attempts) are 82% and 48% respectively, so this is something else to bear in mind.
“There are some wonderful success stories of older maiden mares taking first time but, as a breeder wanting to have a foal on the ground, you need to be prepared and budget for far more attempts,” explains James.
This means there is a need for far greater veterinary monitoring before and during the pregnancy.
“Insemination might be more difficult, and require a greater degree of management, especially if frozen semen is used; the endometrial lining will inevitably degenerate with age, whether a mare has had foals or not. More importantly, older mares are susceptible to what is known as ‘older maiden mare syndrome’, meaning an abnormally tight cervix predisposing her to inflammation and infertility,” says James. “There needs to be much more veterinary input than with a young mare, who might only need to see the vet a few times throughout the pregnancy.”
Temperament and rideability
Caroline Ironside of MFS Studfarm in north-east Scotland breeds from several older mares, all of whom have been at the stud for a long time. Her oldest is 22 this year, followed by two 20-year-olds.
“Most of the mares at the stud are over 14, and all have been with us for a long, long time. This means that we have a really good idea of what they match well with; we know what does and doesn’t work with them, and the type of stallion they can go to,” says Caroline.
“When you see their stock under saddle, you get a much better idea of temperament and rideability – there is less unknown, whereas often with a young mare it’s a complete guess in terms of what they’ll produce.”
Of course, the older the mare the more difficult it is to get her in foal.
“Once they are in their 20s, most will have a foal every second year. We base it on the mare and how they’re looking health-wise,” says Caroline. “If they don’t go in foal then we’ll leave it and try the next year. If they can’t, then we retire them.
“Our 22-year-old Retina S, a KPWN elite mare by Goodtimes x Ahorn Z, took at the second attempt to Eldorado Van De Zeshoek for 2020, and depending on how she looks after the birth we’ll decide whether to have one more foal from her or not,” adds Caroline, who ensures a daughter of her mares remains at the stud, in order to keep the line going. “One of Retina’s daughters is now four and we’re keeping her.”
In terms of management, special attention is paid to nutrition. “Some mares are good-doers and others lose condition quite easily, but you do tend to notice a greater loss of condition as they age – carrying a foal takes more out of them, so we need to supplement a little bit more,” says Caroline. “We take blood samples from older mares, just to check they aren’t missing any essential vitamins or minerals.
“We home-grow our hay and haylage, and the feed is tailored to balance that, so there’s plenty of attention to feeding regardless of age. However, the older mares will have a slightly more tailored diet to be triple sure there are no inconsistencies or deficiencies.”
Emma Blundell of Mount St John Stud adds: “An older mare might not have as much milk, the milk might start losing some of the nutrients, or the colostrum might be of lesser quality. We test all the colostrum irrespective of age, as sometimes it’s not as good and foals will require supplementation, but this is more likely to happen with older mares.”
Independent equine nutritionist Fiona Watkins agrees: “Once the mare’s forage and concentrate requirements are met in full, a breeder may want to look into specific supplementation that may affect milk and colostrum quality. This includes omega-3 fatty acids, vitamin E – particularly beneficial for its antioxidant properties – live yeast and dietary protein.”
When it comes to breeding from older mares, Emma insists that the key is treating each horse as an individual.
“Some mares at 21 look like they’re 16, others less so. They will tell you when they’ve had enough. The conception rates will be lower with older mares: some might get in foal, but will struggle to maintain the foal because of the condition of the uterus,” she says.
“We ensure all of our mares are in top shape before delivery, with regular turnout and time on the horse walker, but I cannot stress enough how much of a physical exertion having a foal involves. There’s lots of extra weight – not just the unborn foal itself but the fluid around it, too – and it’s a lot to carry around all the time, especially towards the end. This inevitably takes its toll much more on an older mare,” explains Emma, whose oldest mare foaling herself is 21, with a couple of others of the same age producing a foal through embryo transfer (ET).
For those who are able, ET – the technique of removing (flushing) an embryo from the uterus of one mare (the biological dam) and placing it in the uterus of a younger recipient mare – can be the best of both worlds.
“It’s such a great way of ensuring you hold on to the really special genetics, but are then able to give the pregnancy to a younger mare who can run around the field and enjoy the process a bit more,” says Emma, who uses ET for around half of her foals.
“We’ve had lots of mares come to us at 18, after their previous owners couldn’t get them in foal, and they’re now still breeding in their 20s by ET with no issues. A great example is Donnerlady, who’s turning 22 – she’s a rare direct Donnerhall daughter and one of the top-producing mares in the Hanoverian studbook, so an incredibly valuable line. Through ET, she’s now given us six foals, and we’re expecting two more next year. She’s been so brilliant for us.”
‘Tricky to handle’
International grand prix rider Nikki Crisp put her retired international grand prix mare Pasoa in foal to her current top horse, the up-and-coming grand prix stallion Durable, when she was 21. In May last year, aged 22, Pasoa gave birth to her first foal, a healthy big colt named Danoa (William).
“Historically Pasoa was so tricky to handle that I never seriously considered ET when she was competing, or inseminating her when she retired at 18; she didn’t owe me anything, and I didn’t want to traumatise her,” say Nikki.
“It was only a few years later as we were having another mare inseminated that I decided to give it a try, almost on a whim, and with the idea that we wouldn’t force it – we wouldn’t induce a cycle, for instance. Surprisingly, she was totally fine with the entire process: because the repro vet was busy with her behind as opposed to her head or neck, she couldn’t have cared less.
“Because of her age there was possibly some loss of elasticity in the uterus and we went for a ‘cross every T and dot every I’ approach, flushing her for a full week, really cleaning her out, and we also had her on Regumate to support the developing embryo. But she scanned in foal first time and gave birth to a huge, healthy colt and now she’s clearly adoring being a mum.”
Pasoa is in foal again to Durable for 2020, this time expecting a filly, who will be her last.
“The one thing we’ll be doing differently this time is that we’ll let her live out even longer, not bringing her in at night until the 11th hour. Obviously, in a 20-something mare you do notice the strain and extra weight more than in a younger mare, and she’s clearly more comfortable if she can keep moving day and night as much as possible,” explains Nikki.
Ref Horse & Hound; 2 April 2020