Latest News Bulletins
Hyperkalemic Periodic Paralysis (HYPP)
Dominique Bouchard, DVM
New England Equine Medical and Surgical center
Dover, NH 03820
“Dream is a 4 year old Quarter Horse mare showing in Halter classes. She is well balanced and has a very well defined and developed musculature. She is sometimes reported to present with muscle tremors and her third eye lid flashing over her eyes after a stressful event. She also seems anxious during the “episode.”
In that case scenario, Dream presents with the classic clinical signs of HYPP or Hyperkalemic Periodic Paralysis. It is an inherited autosomal dominant condition seen in Quarter Horses, Appaloosas and Paints who are descendants from the sire Impressive. In other words, this is a genetic disease that causes a defect in muscle membrane transport. This defect results in increased amounts of potassium (hyperkalemia) in the blood causing an inability of the muscle cells to relax. The dominant character of the condition means that only one mutation of the gene is necessary to express clinical signs. Individuals having two mutations of the gene (homozygote-H/H) are more clinically affected than the horses with one mutation (heterozygote-N/H). When bred, an H/H horse will automatically pass the mutation to their offspring. These animals should not be bred to perpetuate the genetic disease. Since 2007, these H/H horses cannot be registered at AQHA.
Signalment, clinical signs, blood work, response to treatments and DNA genetic testing are used to diagnose the condition in suspected cases. Most commonly clinical signs are seen at the onset of training but are sometimes seen in foals or older horses. Often the first episodes develop after a stressful event such as colic, a dietary change, fasting, weather changes, anesthesia, etc. Each episode can last minutes to hours and can include one or more of the following clinical signs:
-Muscle tremors; usually starting at the head/neck and progressing to the whole body
-Weakness, dog sitting, recumbency
-Prolapse / flashing of the third eye lid
-Sudden death (reported with both N/H and H/H)
Treatments exist to manage the disease and control the clinical signs as well as resolve the signs during an episode depending on the severity. Often management can be performed to prevent episodes. Once it is known that a horse is affected, management of diet and exercise as well as medications can be used to control the disease. Included in management are special diets low in potassium (no alfalfa, brome grass hay or molasses), small frequent feedings, regular exercise, and minimal stress. More severe cases will often need medical treatment during episodes. Dextrose with or without insulin combined with calcium administered intravenously are used to shift the potassium back into the cells. Acetazolamide, a potassium wasting diuretic medication, is used either during an episode or as a daily medication to reduce the frequency and severity of the episodes in affected horses.
Although heterozygote (N/H) animals are still used routinely for breeding, riding, and showing, precautions should be taken when handling or riding those horses. The episodes are unlikely to develop when the horse is exercising, but any abnormal signs should be considered seriously. Eradication of the trait is still a very hot topic in the horse industry.
If you have any questions about HYPP or about matters relating to your horse’s health in general, please talk to your veterinarian about them, or feel free to contact the veterinarians at New England Equine Medical and Surgical Center.
Everyone who foals out a mare knows that colostrum is a good thing. Critical for immune defense in the first several months of life while the foal’s own immune system builds itself up, colostrum is produced by the mare only for a short time after foaling. The foal’s GI tract can only absorb the antibodies contained in colostrum for 12-24 hours after it first nurses, so ensuring that the events of foaling pass normally and the foal stands and nurses (and continues to do so) is extremely important. Foals who fail to do so require supplemental feeding or plasma transfusion to get them through the critical period and prevent problems such as infections and sepsis. However, there exists a situation where mare’s colostrum can be highly detrimental and even fatal to the foal: neonatal isoerythrolysis, or NI.
NI is a condition in which antibodies are produced by the mare against the foal’s red blood cells causing red blood cell destruction and anemia in the foal. This is very similar to Rh factor in human pregnancy when the father passes Rh positive status to the baby and the mother is Rh negative; her body makes antibodies against the ‘foreign’ Rh factor. Almost always, NI occurs with mares who have had multiple foals, and is more likely in the mare’s second foal by the same stallion. Horses have many blood groups, and it is not uncommon to cross a mare and stallion with different blood types and not have a problem. Certain of the blood types are more likely to cause NI than others; mares that do not have a Qa or Aa blood type, and are bred to stallions with Qa or Aa are the most likely to develop problems. If the mare is exposed to the ‘foreign’ blood type either from placental problems during pregnancy or from blood contamination at foaling, her body develops antibodies against the blood type. If the exposure occurs at foaling, the antibody response takes long enough to build that the current foal will not be affected. The next foal by that stallion (or another stallion with that blood type) would be affected because the antibodies are already in the colostrum and absorbed through the foal’s intestines in the first hours of life.
How will you know if you have an NI foal? Usually these foals are born normal, nurse well, and then begin to go downhill within the first few days of life. At their foal check, they usually have adequate passive transfer of antibodies (IgG levels). As the anemia progresses, they become weak, uninterested in nursing, have elevated heart and respiratory rates, and their mucous membranes (eyes and gums) will become yellow with bilirubin, a byproduct of red blood cell destruction. In milder cases, supportive care may be enough to get the foal through the event. Preventing nursing from the mare while providing supplemental feeding, avoiding dehydration, and keeping the foal as low-stress as possible is important. Antibiotics and steroids can be used to prevent infection and reduce the antibody response respectively. After 36-48 hours of life, the intestinal tract of the foal will no longer absorb antibodies from the mare’s milk, antibodies in the milk have declined dramatically, and nursing can be safely reintroduced. If the disease causes severe anemia, a blood transfusion will be required. The ideal donor is the foal’s dam, but the red blood cells must be ‘washed’ to remove all antibodies contained in her plasma. Other donors may be used but cross-matching is important to prevent making the problem worse.
Prevention of NI is possible with a bit of planning ahead. Blood typing the mare and stallion is easily performed with a small amount of blood. If the stallion is bred to many mares, he may already be typed. The mare’s first pregnancy is usually ‘safe’ unless she has had a blood transfusion in the past. In these cases, compatibility should also be checked. If the stallion is positive for Aa or Qa blood type, the mare is negative, and this is not her first foal (a foal by the same stallion is higher risk but remember, previous stallions may have had these blood types and resulted in exposure), she should be considered ‘high risk’ for an NI foal and steps taken in accordance. Muzzling the foal once it stands and before it nurses, and giving colostrum from another mare for 36-48 hours will protect the foal from the dam’s antibodies while ensuring it gets the colostral antibodies it needs. The foal may stay with the dam if the muzzle stays in place. She will need to be milked during this time, not only to keep her comfortable but to remove the colostrum from her udder. There are also tests that can be performed by your veterinarian with the foal’s blood and the mare’s blood or colostrum, to indicate whether there are antibodies present against the foal’s red blood cells.
NI is just one of the many things to think about when it comes time for foaling. As with many foal diseases, early recognition of a problem and quick intervention is key. Having your veterinarian out within the first 24 hours to do a foal check, and then alerting them quickly if anything seems to be abnormal goes a long way to control problems before they get out of hand. If you have any concerns about the possibility of NI in your breeding program, please contact your veterinarian or any of the veterinarians at New England Equine Medical and Surgical Center, to make a plan for prevention. If you have a foal on the ground that you are concerned about, for NI or any other reason, calling the veterinarian as soon as possible increases the chance for a happy outcome.
Susan Barnett, DVM
Jacqueline Bartol, DVM, DACVIM
Watch him drop – Penile cancer in horses
It’s a good idea to be observant when your older male horse urinates in his golden years. Penile cancer in horses typically affects geldings and stallions greater than 14 years of age. They can be located on the prepuce (sheath), although they are more commonly found on the penis. Some horses show no concurrent clinical signs with a penile mass. If the mass is extensive, then you may observe sheath swelling or difficulty urinating if the mass is compressing the urethra. Some cancers can also be ulcerated and may have an odor if they have become secondarily infected with bacteria.
The most common cancer that targets the penis is squamous cell carcinoma (SCC). Light colored horses tend to be predisposed to this type of cancer. They have less pigment in their skin, and sunlight affects the genetic material in the cells causing cancer. There are likely multiple factors, as horses can also get this type of cancer in their upper airway that is not exposed to sunlight.
When you observe a mass on the penis, you should call your veterinarian for an evaluation. The first thing that should be done is a biopsy. Other possibilities for penile masses include parasitic nodules, papillomas (warts) and other tumors (sarcoids, melanoma). It’s important to know what you’re treating, as no one wants to pay for surgery if they can treat a parasitic nodule with a $10 dewormer. If possible, 2-3 biopsies should be taken, especially if there are multiple masses. Although not common, additional diseases can be found on masses that also have SCC. A biopsy of the mass may also tell you how likely the tumor is to metastasize or spread to other organs in the body.
Once you know what you’ve got, then you need to discuss how to go about getting rid of it. There are basically six different treatment options depending on the size and location of the mass, the first two are the most common methods.
1. Surgical excision - This involves excising or cutting the mass away from the normal tissue. This is usually attempted for small tumors or tumors that do not extend into the deeper tissue of the penis.
2) Cryotherapy “cold therapy” - This procedure involves liquid nitrogen, a chemical that freezes the cancer tissue. It freezes the cells, then they die when they thaw after the chemical is removed. This treatment is usually used in conjunction with #1 or for very small masses to decrease the chances of recurrence.
3) Topical chemotherapy - The success depends on the size of the tumor and is variable. Basically it is a topical chemo treatment that is applied daily for a recommended period of time.
4) Surgical removal of mass and healthy tissue -If the tumor extends into the sheath tissue, then this requires cutting off part of the sheath to limit the chances of cancer recurrence.
5) Penile amputation, where a section of the penis containing the mass is removed.
6) Massive penis and prepuce resection and penile retroversion – This procedure is not done often, but is an option for extensive penile tumors that are high up on the penis and/or the horse is having difficulty urinating. Basically the major portion of the penis as well as the whole prepuce (sheath) are removed. The urethra that carries urine from the bladder is significantly shortened and needs a new outlet. This “reconstructive surgery” sutures the new opening below the anus; in effect the male horses start urinating like a female.
Although they have the capability to spread to other organs, squamous cell carcinoma tends to be locally invasive meaning that they just spread to the local lymph nodes. But metastasis to other organs is possible nonetheless. Recurrence rates depend on the extensiveness of the cancer, but in some cases have been as high as 50% and necessitate more than one round of treatment. In effect, it is important to be observant of the older male and to initiate treatment sooner than later with SCC of the penis and sheath. Routine and regular sheath cleaning by your veterinarian constitutes an excellent screening technique.
If you have any questions regarding penile masses, contact your veterinarian or any of the veterinarians at New England Equine.
Karyn Labbe, DVM
Omar Maher, DV, DACVS
Jacqueline Bartol, DVM, DACVIM
Urinary stones in horses
Dominique Bouchard, DVM
New England Equine Medical and Surgical center
Dover, NH 03820
Solo is an 11 year old Warmblood gelding that has been noticed by his owner passing red-colored urine for the past 2 weeks. He urinates more often than normal, passing small amounts at a time and stays in the urination posture longer than normal.
Major potential causes for red urine and difficulty to urinate:
-Urinary stone (urolith): can be in the bladder, urethra, kidneys or ureters
-Trauma: penile, vaginal, urethral or preputial
-Penile masses: usually tumors
-Urinary tract infection
-Acute muscle disorders: for example- tying-up
-Toxicity: for example- red maple toxicity
The most common cause for the clinical signs demonstrated by this horse would be a urinary stone. A urinary stone, or urolith, can be located anywhere within the urinary tract but they are most commonly found in the bladder. This condition is called cystic urolithiasis. Males are affected more commonly than females, although this is a relatively uncommon condition in horses compared to other species such as cats and dogs. Two steps are required to form a urinary stone: first a core of material, called a nidus, must form to set up an origin for accumulation of urinary minerals, called crystallization. Examples of factors that help predispose a horse for urolith formation are prolonged urine retention, incomplete bladder emptying, increased mineral content of the water as well as decreased water intake. Non-steroidal anti-inflammatory drugs such as phenylbutazone also may predispose to urolith formation because of possible kidney function impairment. In addition, once the process is activated, the alkaline (high pH) environment and high level of calcium carbonate mineral in normal equine urine favor crystallization.
Two types of uroliths are found in horses. They can be differentiated visually and by their composition, even though both are composed primarily of calcium carbonate. Type one uroliths are most common. They are a soft yellow-green stone with a very rough, crumbly surface. The rough surface irritates the urinary tract often resulting in bloody urine being passed. Type two uroliths are hard, grey and smooth. In addition to calcium carbonate type two uroliths also contain magnesium and phosphate.
Both urolith types can be detected by a meticulous rectal examination. Rectal ultrasound can confirm the primary diagnosis along with the history and the clinical signs. Urinary endoscopy is helpful when available because this allows visualization of the urinary tract and the stone if it is in either the urethra or bladder. This diagnostic tool helps the veterinarian to evaluate damage caused by the stone(s), determine the number of uroliths present and the upper urinary tract function. Other tests include renal ultrasound to determine if kidney anatomy appears normal, urinalysis and kidney function tests to determine kidney function and bacterial culture for evaluation of concurrent urinary tract infection. Even though urinary tract infections are usually rare in horses, they are often seen along with urinary stones.
Treatment of uroliths includes removal of the stone either surgically (most common in male horses) or manual removal via dilation of the urethra (which is only possible in mares). Optimal treatment will depend of the size, and number of calculi as well as the surgeon’s preference. Antibiotics will also be administered to treat concurrent urinary tract infection as well as post-surgically. Prevention of recurrence of a urinary stone includes attempting to acidify the urine, encouraging increased water consumption, and decreasing the amount of calcium in the diet.
If you have any questions about urolithiasis or about matters relating to your horse’s health in general, please talk to your veterinarian about them, or feel free to contact the veterinarians at New England Equine Medical and Surgical Center.
Eastern Equine Encephalitis
Winter is nearly upon us, bringing mosquito season to a close, and many horse owners are breathing a sigh of relief. Mosquitoes are not only a nuisance but can carry several diseases which can infect horses and humans alike. Of these, Eastern Equine Encephalitis (EEE, ‘Triple E’, or ‘Sleeping Sickness’) made the headlines this year with an unprecedented number of cases in equines throughout New England.
EEE, unlike the name suggests, occurs across the US and parts of Canada, as well as extending into Central and South America. The disease is caused by a virus that is maintained in wild birds, which usually show no signs of disease. The virus reaches high levels in the bloodstream of these birds, where it is picked up by the mosquito and may then be transmitted to a horse (or human) the mosquito later bites. Horses are considered a ‘dead end’ host for EEE, meaning that they do not produce enough virus in the blood to allow transmitting the disease to another animal or human. The peak incidence of this disease is during mosquito season (spring to fall), and tends to be highest late in the summer.
Once the virus is introduced into a susceptible horse, it enters and multiplies in white blood cells and cells lining the blood vessels. The virus then spreads through the blood to nerve tissue in the brain. It may take 1-3 weeks after the virus enters the body for clinical signs to develop. Horses with EEE usually show depression and fever at the outset, and neurologic signs follow. Early on, the horse may show anorexia, ataxia (unsteadiness) and proprioceptive deficits (lack of awareness of limb positioning). The horse may then develop signs such as severe depression or ‘sleepiness’, hyperexcitability to stimuli, compulsive walking in circles, blindness, and have cranial nerve deficits (drooping of the ear, eyelid, or lip, abnormal position of the head or eyes, trouble swallowing). As the disease continues to progress, affected horses will typically become recumbent, unable to rise, and enter a comatose state. Horses who reach this point have a very poor prognosis for survival, and humane euthanasia is typically recommended. Horses who survive severe infection usually have life-long neurologic deficits as a result of the disease. While infection with the disease confers long-lasting immunity against later infection, this is small comfort if the horse is no longer able to lead a normal life. Diagnosis of the disease is often made on clinical signs and an unvaccinated status. Analysis of cerebrospinal fluid (CSF) is the most common laboratory test, and can reveal elevation of white blood cells and protein. It is also possible to recover virus from CSF, or brain tissue post-mortem, though this process takes much longer.
While the disease is devastating to affected individuals, vaccination is highly effective. One of the core vaccines recommended by the American Association of Equine Practitioners, the EEE vaccine is given 1-3 times per year, depending on the level of risk for the disease. While the South is usually thought of as being the place of highest risk, and horses in the Northeast have long been vaccinated only on an annual basis, the recent outbreak would suggest that vaccination at least twice per year would be prudent. The vaccine is usually given in the spring, before the start of mosquito season, but incorporating it into the fall vaccine group is recommended for increased protection. While mosquitoes are not obviously present in the winter, the mild fall weather and earlier spring thaw can result in mosquito presence beyond what we would normally consider ‘mosquito season’. Vaccinated horses who are bitten by an infected mosquito stand an excellent chance of clearing the virus without ever developing clinical signs, and in the few cases in which signs develop, they tend to be far less severe and the horse is much more likely to survive. As they say, ‘an ounce of prevention is worth a pound of cure,’ especially in the case of EEE, where an inexpensive vaccine can save the life of your horse. Mosquito control is another important component to controlling mosquito-borne disease, so eliminate sources of standing water and use insect repellant on horses and humans alike, especially when mosquitoes are most active.
If you have any questions about EEE, other neurologic diseases, or vaccination protocols for horses, please contact your veterinarian or the veterinarians at New England Equine Medical and Surgical Center.
Susan Barnett, DVM
Jacqueline Bartol, DVM, DACVIM
Intestinal parasites – Are worms overpopulating our horses?
Everyone answers, “Yeah, my horse is regularly dewormed.” But these days it doesn’t mean that your horse isn’t still burdened with parasites. Wild horses had the right idea. They dewormed themselves by the low levels of toxins in certain weeds they grazed. Too bad it ain’t free these days. No horse is going to be free of parasites, but we should be educated to know how to control the numbers in our herds. What product to use, when to use it and what it is that we are killing are important questions. Also, what else can I do as a horse owner to limit parasite numbers on my farm?
1). Roundworms (Parascaris equorum), the long worms that you see coming out of your weanling or yearling. The earliest age that youngsters are affected is 3 months considering the worm cycle, so don’t deworm your 2 week old colt. We recommend first deworming for roundworms at 8 weeks old and thereafter treating every 6 weeks. The product? Well, that depends on what you suspect the worm burden is. If the weanling is skinny with a pendulous belly and lethargic, then he probably has more rounds in him that the active weanling of an appropriate weight. So treat the heavily parasitized youngster with Fenbendazole first, then six weeks later go to the more effective Ivermectin. Note that when you treat with Fenbendazole (panacur) specifically for roundworms, you treat with a double dose (10mg/kg) once daily for five days; Ivermectin is the regular dose given once. If you treat the heavily parasitized weanling with Ivermectin, then you could potentially cause a massive die off of the worms and possible impaction of the small intestine. Plus the worms are antigenic and can stimulate a pretty big inflammatory response. The lifecycle of the roundworm larvae involves migration through the lung tissue among other places. Some of these youngsters may also exhibit a cough and snotty nose. Older horses usually more than 1-2 years old tend to gain immunity to roundworms, their immune system may inhibit the migration of the larvae through different stages.
2. Large strongyles (Strongylus vulgaris), not so much a problem since the introduction of ivermection. Aka the bloodsuckers, these larvae migrate through the vessels that supply blood to the intestine causing blood clots and possible death of the intestine. But they could potentially be a problem in areas that don’t have any type of deworming protocol. Recommend Ivermectin to treat with.
3. Small strongyles (Cyathostomes), the larvae of this worm can cause serious diarrhea in horses. Diarrhea associated with these worms is typically seen in late winter or early spring as the encysted larvae in the large intestinal wall excyst. This results in quite an inflammatory response, altered water absorption and watery diarrhea. Moxidectin is pretty effective at killing cyathostomes, recommended to deworm prior to the winter months to decrease larvae numbers. Remember, don’t give moxidectin to weanlings under 5 months of age, as it can have toxic side effects. Can be troublesome to diagnose if infected with the larvae since they are encysted in the intestinal wall. With diarrheal cases will usually see the red worms in the manure.
4. Tapeworms (Anaplocephala perfoliata), high numbers can cause problems in the horse. They have a predilection for the junction between the small intestine and the cecum, attaching to the intestinal mucosa. They may cause enough mucosal ulceration to cause a mild anemia, it’s debated whether they are involved in intussusception (one part of the intestine telescoping into another part). The worm segments look like rice grains. They are eliminated periodicially, so a fecal float may not always show an infected animal. Praziquantel is the dewormer of choice for tapes, recommend deworming with Praziquantel once every six months (twice yearly), give at least one dose around fall time.
At least once yearly your veterinarian should take fecal samples of a percentage of the horses (doesn’t have to be all) on your farm to see whether your deworming protocol is effective. All horses on the farm should be on a similar deworming program and horses dewormed around similar time intervals. Programs are going to be different on each farm, the above are just recommendations. Fecals can also be used to see whether you can decrease the frequency of deworming in some situations, which may decrease the chance of resistance problems on your farm.
Manure control is also important. Manure collected and spread on the pasture just allows parasites to enter their cycle again. Composting is a great option to parasite control. The heat kills worm larvae, as well as also controlling fly larvae and eggs. 3ft by 4ft compost piles that are rotated periodically to mix the compost will usually be complete by 3 months so that the compost can then be spread on the pasture. For the horses already out to pasture, raking the field to break up the manure will allow the sun to dessicate or dry out some of the larvae. Roundworm eggs are difficult to eliminate once in the environment. They can potentially remain infective in the environment for up to 5 years.
If you have any any questions concerning deworming strategies, then please feel free to contact your veterinarian or any of the doctors at New England Equine Medical & Surgical Center.
Karyn Labbe, DVM
Jacqueline Bartol, DVM, DACVIM