One of the most successful veterinary procedures in the field of assisted equine reproduction is one of the oldest ““ the Caslick surgery.
In the 1930s, American veterinarian Dr. E.A. Caslick first performed his simple surgical procedure to correct “pneumovagina,” or vaginal wind-sucking, in broodmares. He had observed that certain mares had an abnormal reproductive conformation that allowed air into the reproductive tract through the vulva. In addition, those mares were notorious “poor breeders,” unable to either get in foal or maintain a pregnancy due to repeated uterine infections.
Dr. Caslick developed a procedure that corrected the vulva, reduced the incidence of infection and restored the mares’ fertility. His findings were published in 1937 in Volume 27 of Cornell Veterinarian.
Since then, his surgery has helped mares with a variety of related reproductive problems and has become commonplace at breeding farms worldwide.
The mare’s outer reproductive tract includes the vulva, vagina and cervix. Those three outer structures provide anatomical barriers that protect the mare’s inner reproductive tract “” the uterus, fallopian tubes and ovaries “” against contamination from the external environment.
The mare’s primary barrier against contaminants (bacterial, fungal or viral) is the vulva. The vulvar lips are held closed together by muscle tone and the way the vulva naturally falls vertically down below the anus.
But when the vulva is compromised (due to foaling injury, poor conformation, advanced age, poor body condition, etc.) so that the vulvar lips gap open or have poor muscular tone, it provides an opportunity for contaminants to enter the vagina. This increases the mare’s likelihood of infection developing in the vagina and making its way through the cervix into the uterus. Uterine infection is uncomfortable for a mare and reduces a broodmare’s fertility.
In a Caslick surgery, the vulva is numbed with lidocaine, and a thin rim of flesh is trimmed from the edges of the top two-thirds of the vulvar lips. The raw edges are then sutured together so that the lips of the vulva heal together and seal together, restoring the vulva’s function as a physical barrier against environmental contaminants.
“The veterinarian should suture the top two-thirds of the vulva, down to just below the pelvic brim,” says Dr. Patrick McCue, reproductive specialist at Colorado State University’s Equine Reproduction Laboratory. “You need to leave about an inch and a half open at the bottom for the mare to urinate through.”
He says, “It is also critical that the vulvar tissue be trimmed in a continuous “˜U,’ so there is a continuous line of excised tissue all along the edges that you want to heal together. That way, the vulvar lips heal together completely, with no openings in the tissue (above the pelvic brim).”
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When a Mare Needs One
The reasons to give a broodmare a Caslick center around preventing contaminants from getting into the vagina and causing infection, especially when the vulva fails as a natural barrier.
“The classic example (and Dr. Caslick’s inspiration) is mares that aspirate air into the vaginal vault,” says Dr. McCue. “Those are mares who aspirate air just by trotting around, because the vulvar lips do not hold together.”
The problem isn’t necessarily the air itself but what the air carries with it: bacteria, fecal material, dirt, etc. Repeated contamination leads to infection, inflammation and infertility.
Wind-sucking is often linked to abnormal reproductive conformation. Normally, the vulva should be vertical, dropping down from the mare’s anus, and the vulvar lips should stay closed together with the mare’s movement.
But when the upper part of the vulva is abnormally angled cranially, so the anus is recessed above it, the vulvar lips are more likely to physically pull apart over the pelvic brim. In addition, fecal material is more likely to enter the vagina. That conformation lends itself to wind-sucking and repeated infection.
“Most Quarter Horses don’t have an abnormal vulva,” Dr. McCue says. “It’s pretty common to find it in Thoroughbred mares or some Appendix Quarter Horse mares.””¨An abnormal conformation can also develop in aged and severely underweight horses, he adds. Regardless, the more angled the vulva and recessed the anus, the more likely a mare is to develop reproductive infections and have a lower pregnancy rate.
Another example is a mare with poor muscular tone in her vulva.
“When we do a reproductive exam on a mare, we check that,” Dr. McCue explains. “You put a thumb and a finger on either side of the vulva and just press out a little bit. In a mare with good muscular tone there, you can’t really pull the vulvar lips apart very much.
“In others, you just apply a minor amount of pressure and the vulvar lips just gape open, and you can hear them aspirate air right into their vaginal vault.”
In addition, if a mare simply has a history of bacterial infection with no obvious reason, Dr. McCue often recommends a Caslick as a precaution.
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Managing a Caslick
In an artificial insemination program, mares in many instances can be bred without having to open a Caslick.
“A person with a small hand and arm can often get under the Caslick to reach the cervix with an insemination pipette,” Dr. McCue says. “Or one can insert a speculum and visualize the cervix, then pass an AI pipette through the speculum, into the cervix and deposit semen into the uterus.”
But in a live-cover program, a Caslick must be opened. Sometimes, a Caslick can be left open while a mare is bred and then resutured when she is confirmed in foal “” especially if she typically has no trouble getting in foal, but has trouble maintaining a pregnancy.”¨However, some mares have a propensity for repeated infection as they come in and out of heat, when they don’t have a Caslick in place.
“In that case, her vulva is blocked, the Caslick is opened, she is covered by the stallion, and then brought back to the stocks to be sutured again,” Dr. McCue explains.”¨A mare that needs the help of a Caslick will typically not be successful in a pasture-breeding situation.
“For pasture breeding, a mare needs a normal vulva, because that breeding is not assisted or controlled,” Dr. McCue says. “A stallion cannot penetrate a Caslick, so you can’t leave one in her while the stallion is turned out with her. But if she has problems with repeated uterine infections, she either won’t get in foal or stay in foal without the help of a Caslick.
“If a mare would be helped by a Caslick, she’s probably going to be open in a pasture-breeding situation.”
A Caslick must be opened prior to foaling.
“You would not want to allow a mare to go into labor with a Caslick still intact,” Dr. McCue says. “She will tear, and it can cause significant damage.
“About a week or two prior to her due date, she needs to have the Caslick opened up. If she bags up early, open the Caslick early.”
To open the Caslick, the vulva is numbed and surgical scissors are used to separate the healed-together tissue, along the line of the suture scar.
In Quarter Horses, Dr. McCue says, a Caslick is generally performed for a specific reason and not as a standard practice on every broodmare. Additionally, a broodmare can have a Caslick procedure performed annually for many years without significant issues.
“There is an alternative procedure that can be performed that eliminates the need to remove a rim of tissue from the vulva,” Dr. McCue says. “That is to simply block (numb) the vulva with Lidocaine and then use a scalpel blade to make a “˜U’-shaped incision along the rim without removing tissue. In my opinion, this procedure is actually easier to perform than a traditional Caslick.”
He adds, “Not very many veterinary procedures initially developed in the 1930s are still being performed some eight decades later. The Caslick has stood the test of time and will likely be around for the foreseeable future.”
From The American Quarter Horse Journal, America’s Horse Daily, September 5, 2014
photo courtesy of the Journal.