Advances in veterinary medicine and equine care mean today's horses, just like today's humans, are living longer, more productive lives. In addition to being used in competition, equine senior citizens are being used more frequently in breeding programs. But while there are many benefits to breeding older stallions and mares, there is a catch. Data indicates that older mares—mares 16 years old and older—are less likely to have foals than younger mares. Older stallions—those in their late teens and 20s—are less fertile than younger stallions. However, good breeding management, accurate testing, and medical and surgical therapies can often increase the breeding life of both mares and stallions.
Older Mares
Why would a breeder choose to use an older broodmare? To propagate the good genes of performance mares, according to Dr. Donald Hunt, a veterinarian at Middlebury Large Animal Clinic in Middlebury, Vermont. A mare who has been used in competition may be eight or 10 years old before having her first foal, and be several years older—often in her mid-teens—before her first foals are old enough to perform. If a mare with a good performance record produces foals who perform well, that mare's value increases significantly, and additional foals are in demand. This is the main reason why owners want older, proven broodmares.
Unfortunately, by the time a broodmare is considered proven she is facing a reduction in her reproductive ability.
"You are most likely going to have a poor conception rate with older mares," Dr. Hunt said. "There are many things that cause reproductive issues with older mares, and there are various ways to treat them, but the breeder must be prepared to spend more time and money getting the mare in foal."
Contamination and infection, both of which cause inflammation, are the primary reasons for poor reproduction. Inflammation can destroy the semen or the embryo. The cause of contamination and infection in older mares is usually poor conformation, including decreased uterine clearance, poor vulva conformation, and increased scar tissue of the uterus and cervix, according to Dr. Laura Carmel a veterinarian at Tufts School of Veterinary Medicine in Medford, Massachusetts. Ultimately, these conformation problems affect the anatomical barriers that help keep infection out of the reproductive tract.
One of the most common conformational problems in the older mare is the tipped vulva. "This is when the vulva is not perfectly vertical," Dr. Hunt said. "The muscles stretch and it becomes more horizontal, which allows feces, dirt, and air to enter the vagina. This problem can often be remedied with a Caslick's operation, in which the vulva lips are sewn to prevent the contaminants from entering.
Another common problem the breeder might encounter, according to Dr. Carmel, is decreased uterine clearance. This is when mares retain fluid in the uterus, which causes inflammation, infection, and often prevents pregnancy.
"Any time you breed a mare you are going to get infection," Dr. Hunt explained. "It is normal for the mare to have a certain amount of fluid in the uterus after mating. Normally, the sperm causes a release of white blood cells, which then expel the semen and dead sperm. Older mares are often unable to expel the results of insemination." To improve uterine clearance, mares can be treated with a lavage, in which the uterus is flushed with warm saline, hours after breeding. A dose of oxytocin may also be administered.
Dr. Carmel said that careful ultrasound examinations, a speculum exam, and a uterine biopsy can increase success when breeding the older mare.
Dr. Hunt concurred, "If you are going to breed an older mare, that mare should have a good reproductive workup. Make sure she is not infected by culturing her when she is in heat. A speculum exam in the vagina will let you know if there are adhesions or abscesses, and will tell you the condition of the cervix. If there is a fair amount of monetary consideration I would also biopsy the uterus for adhesions and glandular changes to see what the tissues look like. Cytology can be done to look for bacteria. Do a rectal ultrasound to survey the ovaries and uterus. If the mare has a poor biopsy the chance of conception is down around 5 percent."
If the breeder is satisfied with the reproductive workup and wants to breed the mare, there are steps he or she can take to boost the possibility of success.
One of the first things the breeder can do is choose a stallion who has a high number of motile sperm with a longer life span. A stallion who has sperm that last for two days, versus a stallion who has sperm that last a half day, is a better choice for the older mare.
Also, to minimize contamination, older mares benefit from breeding techniques that are more sterile, such as artificial insemination using fresh cooled semen, according to Dr. Carmel. Not only is it cleaner, but you can control the volume of semen that is put in the mare.
Older mares should be bred at the optimum time, which is 24 -48 hours before ovulation.
If you have an older, proven broodmare, it is important to keep her in foal. "If you have a good mare you have been breeding right along it is best to keep her bred to keep the fertility level up," Dr, Carmel said. Every year a mare is left open, it decreases her chances of conceiving.
Dr. Hunt added, "Older mares who have been bred consistently tend to do pretty well when their reproductive systems are kept in working order. The horse who is 17 and has never had a foal and is fat . . . she is a challenge."
Other issues include scarring of the uterus and cervix, aged eggs, hypothyroidism, overuse of antibiotics, genetics, uterine cysts, repeated foaling, and not foaling enough. General health, including nutrition and fitness, also play a role in getting the older mare in foal. A vaccination program; regular deworming, dental, and foot care; keeping the mare in good body condition; and feeding hay that is dust-free, leafy, green, and nutrient-rich also play a part in the mare's reproductive success.
When all else fails, there is technology that can help older mares pass on their bloodlines. Embryo transfer and oocyte transfer are two common options. Both techniques take the oocyte, or egg, from the proven mare and use a surrogate mare to carry the pregnancy. However, these methods do not work with mares whose reproductive problems are associated with the age of their eggs. While some older mares may not have difficulty getting in foal, they do have older eggs, which are often susceptible to early embryonic death.
How do you know when to retire your older mare? Dr. Hunt said, "If there has been an effort for two years using a good, fertile stallion and good breeding techniques, and you have bred the mare three times per season without pregnancy, then I would say it is time to retire that broodmare."
Dr. Carmel said, "If the breeding has been done properly and managed accordingly I would give it five cycles. Also, if the mare has lameness issues or poor body condition that would be exacerbated by extra weight I would retire her."
The Stallion
While five to eight years of age is the most fertile time for a stallion, some stallions are able to breed well into their 20s. The reasons for using an older stallion are similar to those regarding using an older mare—the desire to pass on proven bloodlines. While stallions have the added advantage of being able to perform and breed in the same time period, many breeders like to use older stallions retired from the competition ring as breeding animals. Stallions with proven offspring on the ground are very valuable, and as their value increases so does the value of their subsequent foals.
Before advertising a stallion, a breeder should first determine that the stallion is producing live sperm cells. The semen quality—the primary issue facing older stallions—can then be evaluated. "Decreased quality and decreased volume are the primary problems that breeders of older stallions encounter," Dr. Hunt said.
He suggested that breeders evaluate a horse's breeding strength by running a sample, collected using an artificial vagina, through a number of tests in which volume, motility, and pH are determined. "Sometimes we'll collect a stallion sample and everything looks good, but the stallion is still not getting mares in foal," Dr. Hunt said. "In this case you can check DNA, which is a fairly reliable test. It will give the breeder a good indication of where the problem is occurring."
It is also important for the breeder to know that some stallions do not ship as well as others. "If your stallion's breeding soundness exam shows no problems, and you are shipping your stallion's semen, process the semen in the equitainer and then evaluate it again," Dr. Hunt said. "It is possible the stallion's semen does not ship well." There is an even greater variation in frozen semen, according to Dr. Hunt. Only 25 percent of stallion semen can be frozen and result in a good, viable sample.
Artificial insemination is generally the breeding technique of choice for those using older stallions. "If you are using an older stallion, who may have physical disabilities such as arthritis, collection on a phantom mare is probably the best way to go," Dr. Hunt said. "The older stallion may hesitate to jump a live mare because he doesn’t want her to move. The phantom is not going to move. Also, when you use artificial insemination you get a chance to evaluate the sperm so you know whether to ship more, less, or not at all."
Dr. Carmel said, "If a stallion has arthritis in the hind legs you can teach him how to be collected standing on the ground. Arthritic pain, which makes a stallion unable to mount, is one of the main issues the breeder of an older stallion will encounter."
If the volume, concentration, or viability of a stallion's semen is not adequate, deep horn insemination is possible. This is when semen of poor quality is put through the cervix, in the tip of the uterus by the tip of the oviduct. "We have had some success with this method," Dr. Hunt said.
How do you know when to retire your aged stallion. When the semen looks completely dead, according to Dr. Hunt. Dr. Carmel said poor results from a breeding soundness exam, showing 30 percent progressive motility and 60 percent abnormal morphology, would indicate the stallion's breeding career has come to an end.
