Check out this informative article from thehorse.com ...
We are sorry to announce that Horsemen’s Laboratory will no longer be selling the EquiSal Tapeworm Test Kit. Due to unforeseen ongoing issues with customs and excise, EquiSal Tapeworm will no longer be sold in the US. Austin Davis Biologics Ltd. is investigating alternative ways to bring tapeworm testing to the US in the near future.
If you have purchased an EquiSal Tapeworm Test Kit and would like to have a saliva sample tested please collect and return your horses’ saliva sample to Horsemen’s Laboratory by October 29, 2017 so that it can included in our final shipment to the UK on October 30, 2017. Otherwise please contact us for a refund for any un-used EquiSal Tapeworm Test Kits.
Please contact Austin Davis Biologics Ltd. at firstname.lastname@example.org if you have any additional questions concerning EquiSal Tapeworm.
Once again, we apologize for any inconvenience this may have caused you.
By Dr. Kenton Morgan, managing veterinarian, Equine Technical Services, Zoetis
For horse owners in parasite-prone areas of the country such as the Southeast, their deworming program could be teetering on the fence of responsibly controlling parasite burden or unintentionally contributing to parasite resistance.
Within temperate environmental conditions that are key for parasite survival, horse owners may be tempted to deworm every few months in an attempt to reduce their horse’s parasite risks; however, by deworming every few months, horse owners can inadvertently do more harm than good — increasing the horse’s risk for parasite resistance. When parasites are overexposed to certain active ingredients, they can become resistant, leaving fewer effective treatment options.
To determine prevalence of anthelmintic (deworming treatment) resistance, a 2004 study examined 786 horses on 44 farms across Florida, Georgia, South Carolina, Kentucky and Louisiana. Fecal egg count reduction tests were conducted, and results demonstrated farms with anthelmintic-resistant cyathostomes (encysted small strongyles) was highest at 97.7% for fenbendazole (Panacur®, Safe-Guard®). The prevalence of resistance found in the study is higher than previously reported, which suggests a growing problem of parasite resistance.1
The Gluck Equine Research Center evaluated the safety of moxidectin, the active ingredient in Quest® and Quest® Plus Gel, as well as other products. Examining inflammatory reaction within the intestinal walls, the studies suggest moxidectin presents very little inflammatory response in the large intestinal walls, thus offering a safer choice for treatment of horses with large burden of encysted small strongyles. “Similarly, moxidectin may qualify as drug of choice for treatment of larval cyathostominosis, and could possibly replace the long-term treatment regimes involving several alternations between fenbendazole and ivermectin that were previously suggested. However, further studies are needed to verify these assumptions fully,” according to the report. 2
With just a single dose, Quest and Quest Plus Gel continue to demonstrate safety and efficacy in treating and controlling encysted small strongyles, bots and roundworms. 3,*
Because every horse is unique, I encourage horse owners to work with their veterinarian to perform an annual fecal egg count (FEC) test to determine their horse’s parasite levels and efficacy of treatment. The American Association of Equine Practitioners (AAEP) considers an FEC test to be the best assessment of parasite burden to identify the frequency of treatment needed. Once a baseline is established, horse owners can work with their veterinarian to develop an Individualized Deworming™ plan tailored to their horse’s needs.
The following factors contribute to equine parasite risk and, with an FEC test, can be used to determine your horse’s individualized deworming plan:
Yearlings and 2-year-olds should continue to be treated as “high” shedders (those with an FEC of 500 or above) and receive three to four yearly treatments. Horse owners can determine deworming needs for mature horses with an FEC test, conducted by the horse’s veterinarian, to identify the frequency of deworming treatment needed to target small strongyles, tapeworms, bots and spirurid nematodes, which are responsible for causing summer sores (Habronema spp. and Draschia spp).
For additional information and resources, visit QuestHorse.com.
Do not use Quest Gel or Quest Plus Gel in foals less than 6 months of age or in sick, debilitated and underweight horses. Do not use in other animal species, as severe adverse reactions, including fatalities in dogs, may result.
Zoetis is the leading animal health company, dedicated to supporting its customers and their businesses. Building on more than 60 years of experience in animal health, Zoetis discovers, develops, manufactures and markets veterinary vaccines and medicines, complemented by diagnostic products, genetic tests, biodevices and a range of services. Zoetis serves veterinarians, livestock producers and people who raise and care for farm and companion animals with sales of its products in more than 100 countries. In 2016, the company generated annual revenue of $4.9 billion with approximately 9,000 employees. For more information, visit www.zoetisUS.com.
For more information, contact:
1 Kaplan RM, et all. Prevalence of anthelmintic resistant cyathostomes on horse farms. JAVMA. 2004:225(6);903- 910.
2 Betancourt A, Lyons ET, Horohov DW. Characterization of the inflammatory cytokine response to anthelmintic treatment in ponies. Equine Veterinary Journal. 2014.
3 Mason ME, Voris ND, Ortis HA, et al. Comparison of a single dose of moxidectin and a five-day course of fenbendazole to reduce and suppress cyathostomin fecal egg counts in a herd of embryo transfer-recipient mares. J Am Vet Med Assoc. 2014;245(8):944-951.
4 American Association of Equine Practitioners. AAEP Parasite Control Guidelines https://aaep.org/guidelines/parasite-control-guidelines. Accessed August 15, 2017.
* This study compared Quest (moxidectin) Gel with Panacur Powerpac (fenbendazole).
All trademarks are the property of Zoetis Services LLC or a related company or a licensor unless otherwise noted. Panacur and Safe-Guard are registered trademarks of Intervet Inc. or an affiliate.
© 2017 Zoetis Services LLC. All rights reserved. QST-00095
The staff and owners of Horsemen’s Laboratory are like all other businesses we love our loyal clients. This is a short story about just one of our many loyal clients and her horse Herz. Ginger Krantz sent Horsemen’s Laboratory Herz’s first fecal sample on May 5, 1993 for a fecal egg count. Horsemen’s Laboratory received Herz’s latest sample on May 19, 2017. Herz was 7 years old when we received his first sample and now 24 years later he is 32 years old. Over the 24 years Horsemen’s Laboratory received 63 samples for evaluation and only 9 of those samples were positive and then for only 50 strongyle eggs/gm the lowest number we record. No other worm eggs were found. When I asked Ginger how many times she dewormed Herz over the 24 years she immediately replied 9 times after each positive test. Ginger moved Herz to several different stables situations over the 24 years and yet he never had an egg count over 50 strongyle eggs/gm. His last positive test was 50 strongyle eggs/gm on November 9, 2012 almost 5 years ago.
Horsemen’s Laboratory wants to thank Ginger for her loyalty and reward her for her diligence in protecting her horse Herz from worms by having his stool checked so often. Therefore, John W. Byrd, DVM owner of Horsemen’s Laboratory said we would check him for worm eggs for free for the rest of his life.
Horsemen’s Laboratory has several other clients that have their horses worm control programs evaluated by us, but none of them have one horse that we have been evaluating over as long a period of years as Herz or as many times.
If you are a client of Horsemen’s Laboratory and feel you have a special story you would like to have told concerning your horse and how Horsemen’s Laboratory has helped you evaluate your horses’ worm control program please contact us and let us share it with our other clients.
Here’s Ginger & Herz’s story …
Dr. Byrd and Horsemen’s Laboratory have made a significant, positive difference in the life of my German Warmblood gelding, Herz. When I purchased him, in 1989, he was 4 years old. I’d recently enrolled in a four-year training program in Brennan Healing Science®. With health being a primary value, I sought to make educated decisions about his management. Soon I began to question some conventional methods of horse care, and sought to reduce his intake of toxins. Working with my veterinarian, I minimized his vaccinations. I made dietary and supplement changes. When I learned about Horsemen’s Laboratory, in 1993, I shifted from the accepted norm of routine paste worming every six weeks; to testing for egg counts quarterly, and worming as needed.
In our 28 years together, Herz has lived at four different farms, in two states. Any time, I’ve had a concern or question about worms, or my horse’s fecal results; Dr. Byrd has been available for consultation. He’s informed me with his data, and facts from the latest research; enabling me to make the best, educated choices for my horse. As a result, in the past 24 years, Herz has had positive stool sample only nine times, and his egg count has never been above 50. Tracking his fecal counts, has allowed me to minimize his intake of chemical wormers, toxins and stress on his digestive system. The fecal reports have also made it possible for me to surmise why he obtained worms, in each case.
From my personal healing journey, and passion to help horses and their owners, I’ve created Earth Horse Healing, a holistic healing practice that specializes in horses. Over the years, I’ve clearly seen the positive difference minimizing toxic load and stress has on horses. I’m grateful to Dr. Byrd, for having the foresight and dedication to create Horsemen’s Laboratory. He’s given me, and the many people I’ve referred his service to, the opportunity to take their horses’ worming programs into their own hands. Thanks to Dr. Byrd, my horse has been spared countless doses of paste and daily wormers. Horsemen’s Laboratory has contributed to Herz, at 32 yrs, still being with me, today.
Earth Horse Healing: http://earthhorsehealing.com
Earth Horse Healing Facebook: https://www.facebook.com/EarthHorseHealing/
Horsemen’s Laboratory has donated $1,000.00 to American Association of Equine Practitioners to support their relief efforts in helping horsemen and women affected by Hurricane Harvey. Horsemen’s Laboratory has also committed to donating $1.00 from the sale of every kit sold in the month of September to this relief effort.
Order kits today and help us raise additional funds to support those in need.
If you would like to make a donation directly to the AAEP you can visit: https://foundation.aaep.org/form/foundation‐donation
The American Association of Equine Practitioners (AAEP) Foundation’s Equine Disaster Relief Fund is accepting aid to help horses in Texas, Louisiana and other states affected by Hurricane Harvey. Fund donations will be distributed among credible programs and organizations that are helping with recovery and rebuilding efforts in the aftermath and towards preparedness efforts for future disasters.
The AAEP Foundation, a 501(c)(3) organization created in 1994, serves as the charitable arm of the American Association of Equine to improve the welfare of the horse. Since its inception, the Foundation has disbursed more than $4 million to support its mission.
Recently Horsemen’s Laboratory was asked what other practices an owner can use to control worms in addition to deworming, especially for the worms that cause summer sores (Habronema).
Since Habronema larvae are spread by stable flies and house flies, the best practice to help control them is to control the fly population in your horses’ environment. The Habronema larvae are passed in horse manure, when flies feed on the manure they actually take in the microscopic larvae. These larvae develop and when the flies feed on a horse’s wound or around the eyes, lips or other areas of the horse that are moist the larvae moves to the mouth parts of the fly then they get into the small wound that the fly makes as it feeds on the horse and burrow in to the tissue of the horse. Fly larvae (maggots) may also eat the Habronema larvae which will live in the fly until the fly becomes an adult. Once in the tissue it is thought the larvae causes considerable inflammation. Some believe that there is a severe allergic local reaction to the larvae that causes the severe inflammation that creates a deep ugly ulcer from ¼ inch to several inches in diameter. Some owners claim the fly predators help reduce the fly population a great deal around the stable.
Other worms and practices that help control them:
Pick up manure in stalls, paddocks and pastures as often as possible.
Be sure it is going to be hot and dry for several days when you mow or drag pastures and best to pick up manure before mowing or dragging. One should also strongly consider keeping horses off the pasture for 2-4 weeks. Since mowing and dragging pastures spreads the infective eggs and larvae over a much larger portion of pasture area making it hard for the horses to avoid eating them.
Cleaning pastures at first sounds like a big task, however, most horses seem to divide pastures into two distinct areas; lawns and roughs. There are also pasture vacuums now available to be pulled behind a tractor that will actually vacuum your pastures.
Once the lawn and rough areas have been established you most likely will only have to pick up the rough area, as 90% of the worm eggs will be passed in those areas. Strongyle larvae general take 2-3 days (in the summer under ideal conditions 24 hours) to reach the infective stage and they do not leave the pile of manure they were passed in until they reach the infective stage.
Following the routine we have described for keeping stalls, paddocks, and pastures cleaned will have a very positive affect on reducing the number of infective eggs and larvae that your horses are exposed to. As opposed to deworming that only kills the worms that are adults.
In conclusion, picking up the manure piles on a routine schedule will reduce your horses’ exposure to a much higher number of worms than deworming. However, deworming is still an essential part of worm control. Therefore, following all the recommendations above will greatly reduce your horses’ risks of problems caused by worms that we described in an earlier article.
Large strongyle larvae penetrate the large intestinal wall and migrate through different abdominal organs. There are 4 species of large strongyles, Strongyles vulgaris, Strongylus edntatus, Strongylus equinus, and Triodontophorus. Until around 1980 Strongylus vulgaris was the most harmful worm in horses. The larvae migrated through the abdominal organs and into the main artery that supplies the intestine known as the cranial mesenteric artery. Where this artery comes off the aorta these larvae seemed to gather. They caused considerable irritation to this area with the formation of blood clots and degeneration of the artery by disrupting the lining and weakening the artery wall. This occasionally caused an aneurysm of varying size to form, which allowed serum to leak from the artery and even occasionally was said to lead to rupture of the artery and sudden death of the horse. The blood clots that formed often were said to break off and travel down the artery obstructing the smaller braches of the artery thereby restricting the blood supply to a section intestine. Without proper blood supply the section of the intestine did not have the normal peristaltic movement and often the horse developed colic. This colic was named Thrombo-embolic colic, one of the few large terms I still remember from vet school. After this the larva travel back to the intestine and become adults and continue to cause the horse problems by attaching to the intestinal wall and sucking blood causing the horse to become anemic. This characteristic plus the fact the larvae travel in the blood stream gave this worm the name Blood Worms. When I first got out of vet school I dewormed a small herd of horses for a client in December. It snowed about 3 inches that night and the client called the next morning in a panic and claimed I had poisoned his horses. I rushed back to the farm to find that each pile of manure the horses had passed in the snow had very fine steaks of very bright red leading away from the pile a few inches to a foot. When examined carefully each streak had a dead worm at the end of it. The streak was due to the passage of the blood the worm had passed as it crawled away from the pile of manure. When Ivermectin came on the market around 1980 it was very effective against Strongylus vulgaris because it was absorbed from the intestine and would kill the larvae that were migrating through the horse. It was thought that the use Ivermectin would eventually eliminate worms; however the worms had a different idea and are still a threat to horses. Strongylus vulgaris is not nearly the threat it once was but still can be found if searched for. The deworming routine that was started back in the 70s and 80s may now be responsible for the development of the resistance to deworming medication we are seeing in worms to today.
The other large strongyles are less of a problem but can cause some significant harm if in large enough numbers. They have not been nearly as harmful as Strongylus vulgaris. Triodotophorus is unique in that is fits into the large strongyle size category but it does not migrate in its larval stages but becomes encysted as small strongyles do.
Between 30%-33% of the samples examined by Horsemen’s Laboratory are positive for worm eggs. 95% of the positive samples are positive for strongyle eggs. Research tells us likely only 5% of those eggs are from large strongyles. Most strongyle eggs appear very similar under a microscope. The eggs must hatch and the larvae must be examined to tell which species of strongyles are present. Most often it is a mixture of several different species.
Small strongyles have several names. One is scientific Cyathostomins. Another is non-migrating due to the fact unlike migrating or large strongyles that the larvae migrate through several abdominal organs. Small strongyles only burrow into the mucosal lining of the large intestine and become encysted there normally for 2-3 weeks, but may remain encysted and viable for 2.5 years. They are now by far the most common parasite of horses. Dr. Nielsen and Dr. Reinemeyer state in their book Handbook of Equine Parasite Control there are over 50 species of small strongyles. They have similar life cycles and common modes of pathogenicity (ways of causing disease). The eggs of all strongyle species are very similar and cannot be used to identify which species are present. The main problem caused by small strongyles is the inflammation that the larvae cause in the large intestinal wall when they encyst. The adult small strongyles do not cause the horses much problem even when in high numbers. They do not attach to the lining and suck blood as large strongyles do. Sometimes large numbers of encysted larvae encyst at one time and rarely cause a syndrome termed Larval Cyathostominosis. Due to the substances released being somewhat toxic and the inflammation caused by the encystation of the large number of larvae the horse can develop this syndrome characterized by profuse diarrhea, weight loss, anemia, hypoproteinemia, ventral edema, and dehydration (Dr. Nielsen and Dr. Reinemeyer). This syndrome is difficult to diagnose. Larval Cyathostominosis most commonly occurs in young horses between 1-4 years of age. This syndrome may appear somewhat seasonal. Within the northern climates occurring in winter or early spring, in warm climates occurring in the summer. It may occasionally occur after deworming. What causes the larvae to remain in the cysts is unknown but due to when these large encystations occur it may have to do with the number of adults in the intestine. As the number of adults present in the intestine drop it seems a signal is sent to the larvae to leave the cysts. Just because this syndrome is discussed here is not intended to cause owners to worry. Horsemen’s Laboratory has examined over 70,000 samples since 1992. Between 1/1/14and 1/1/16 we examined 29,976 samples with 19,000 negative (63%) (No worm eggs found on counting chamber) and 11,108 (37%) samples were positive. 1563 (14%) of the positive samples were over 1000-strongyle eggs/g of stool. We have never have had a report of a horse developing c. This may be because most our patients are mostly older horses. What I am trying to illustrate is that Larval Cyathostominosis is not a common problem just because horses have a fairly high number of small strongyles.
By John Byrd, DVM
Problem #6: Death
Please be sure to read the last paragraph of this article.
Deaths in horses have occurred in the past due to worms and may continue to occur, but at a much reduced rate. The introduction of Ivermectin as a deworming medication has been a large factor in the decreased death rate from worms. It has nearly eliminated Strongyle vulgaris and other large Strongyles that were the major cause of death in horses from worms. As indicated previously, Strongyle larvae can cause severe damage to the arterial supply to the digestive tract. Blood clots, emboli, and aneurisms were the result of large Strongyle infections. The finding of these problems is seen much less today during colic surgery and necropsies. Small Strongyles now can cause death due to large excystation of small strongyle larvae with development of the syndrome termed Larval Cyathostminosis.
Most deaths in horses thought to be due to worms are due to several factors and worms are only one contributing factor. Horses that are suffering from inadequate nutrition, viral or bacterial infections, and other stress are much more likely to die from worm infections.
The number of horses that die from worms is a very small (probably minuscule) number and owners should not read this article and become worried that their horses are going to die or even that worms are going to effect their performance. I know for a fact that I could put 5 horses in a ring and ask expert horsemen to rate them according to how many worm eggs they are passing and it would be pure luck for them to get the rating correct. I say this not to be critical, but to show that horses can be fat, slick (have a beautiful hair coat) and energetic and still we find 2000-3000 eggs per gram of strongyle eggs in their manure. One of the first horses I tested when I moved back to Illinois had just won a major Quarter horse futurity a few days before I personal took the sample and it was positive for 5000-strongyle eggs/gm of manure. Dr. M. K. Nielsen one of the authors of Handbook of EQUINE PARASITE CONTROL did a study on fecal egg counts in 213 racing Standardbred horses in Denmark with the following results. There was a statistical difference in the fecal egg count in the horses finishing 1-3 in a race as compared to those horses finishing unplaced. The actual results were unexpected. Horses finishing 1-3 actually had a higher fecal egg count than those finishing unplaced.
To keep from worrying about worms in your horses do periodic (Horsemen’s Laboratory recommends every 3 month at least until it is established what egg shedding category they are in) fecal egg counts to evaluate the effectiveness of your horses worm control program and go enjoy your horse.
By John Byrd, DVM
Problem #5: Tail Rubbing
The characteristic tail rubbing associated with worms is generally due to pinworms. The female pinworm partially exteriorizes itself and lays her eggs around the rectal ring. The eggs stick to the skin with a substance similar to egg whites. This substance causes an itchy sensation causing the horse to rub its tail on feed tubs, posts and other objects causing self-inflicted superficial skin irritation sometimes almost appearing as an ulcerated area.
By John Byrd, DVM
Problem #4: Ulcers
Bots, Draschia megastoma and Habronema musccae are 3 classes of worms that can be responsible for ulcers in the stomach. Bot worms are the larval stage in the cycle of a Bot fly. They look like a small honeybee and they fly around horses’ legs, gluing eggs to the hair on the horses’ front lower legs. When licked by the horse these eggs hatch and the larvae attach to the horse’s tongue. Then they burrow into the horses tongue and gums and find their way to the stomach where they attach to the mucosa. When large numbers of larvae attach, they do it in close proximity to each other and when they all release their attachment at one time a fairly superficial ulcer is revealed. These ulcers are generally not very severe.
Draschia megastoma (largemouth stomach worm) and Habronema musccae live in the stomach. Draschia megastoma can cause nodules in stomach that can be like an abscess that can rupture into the stomach or into the abdomen. Fortunately this is very rare. Habronema cause some irritation to the lining of the stomach. Stable and houseflies carry the larval stages of these 2 worms. When the flies feed on the horse’s skin, the larvae leave the flies and get into the wound and can cause severe skin ulcers that are commonly known as summer sores. Summer sores most often are seen in horses in the southern states and California. The ulcers are frequently seen in the corners of the eyes and lips, and in geldings and stallions, they form on the penis and sheath.
Tapeworms sometimes appear to be responsible for ulcers in the area of the intestine where the small intestine connects to the large intestine. These ulcers seem to be due to tissue damage caused by the attachment of the worm’s mouthparts, especially when there are large numbers present. These ulcers have been observed during colic surgery and during necropsies.
Most ulcers in the digestive tract of horses are not caused by worms, but by stress or some other disorder that affect the bacterial flora or cause chronic irritation to the gut.
By John Byrd, DVM
Problem #3: Chronic cough, Runny nose
Round worms can also be responsible for coughs and runny noses in young horses most often under one year of age, but may even occur in horses slightly older. One stage of the life cycle of the roundworm is larval migration to and through the lungs. During the migration through the lungs the larvae may cause considerable inflammation that may be considered a type of pneumonia. Pneumonia is frequently complicated with a viral infection and occasionally with bacterial infections. Often I am asked how much permanent damage is done to the lungs during the time the larvae are in the lungs especially when horses are to be used as performance horses later in life. I have seen horse that had fairly severe roundworm infection with severe respiratory signs that went on to be outstanding racehorses and other performance horses. I have discussed this with pathologists that perform necropsies on horses and they have told me they seldom see much residual damage to the lungs even though the respiratory signs were severe when the horse was young.
Chronic coughs can be caused by lungworms in any age horses that are kept with donkeys. It seems that the lungworm causes little if any problems for donkeys, but when a horse gets them they cause a dry chronic cough. The larvae are coughed up and passed in stool, but are seldom found. In donkeys the larva develops into adults in the lungs and passes eggs that can infect horses that are grazing with the donkeys. However, in the horse the larvae do not develop into adults and pass infective eggs, therefore; the horse is considered a dead end host. In order to make a diagnosis of lungworms a sample should be taken from the donkeys that are grazing with the horses.
By John Byrd, DVM
Wormy Horse Syndrome: Weight Loss, Diarrhea, Stunting, Poor Hair Coat, Depression, Poor Appetite, and Potbelly appearance
I have elected to discuss all these problems together because they all appear to occur together. The problems are generally seen in young horses less than 2 years of age. They are most often seen in poorly managed breeding operations where young horses have been raised in the same pasture or paddocks for several years. There are 3 major factors that seem to be responsible for this.
Weight loss, stunting, poor hair coat, and depression can also be due to the heavy load of worms using up a great deal of the energy that these young horses need to grow. In the case of roundworms, just the large mass of roundworms in the small intestine can interfere with the absorption of nutrients that takes place in the small intestine. Due to the lack of needed nutrients the horse will become depressed and its appetite will also be depressed. Often these young horses are infected with several different classes of worms. It is not uncommon to find large numbers of roundworm eggs and strongyle eggs in a young horse’s fecal sample. Recently, we had a couple yearlings that also had tapeworm eggs in their stool. These worms are all competing with the young horse for the nutrients it is taking in. The large strongyles are particularly bad because the adults attach to the intestinal wall and actually suck the horse’s blood. Soon after I graduated from vet school I recall deworming a large herd of horses, it had snowed a few inches overnight and the next morning the owner called me in a panic because he thought I had poisoned his horses. From each of the fresh manure piles there were little red streaks on the fresh snow. I rushed back to the farm and what we found was that each streak had a dead large strongyle at the end of it filled with pure blood. Many weanlings have suffered and died of anemia due to severe large strongyle infections. Fortunately, shortly after that Ivermectin came on the market and has tremendously reduced the population of large strongyles, but has not completely eradicated them as we had hoped.
Diarrhea can occur when there are extremely large numbers of encysted strongyle larvae in the wall of the large intestine in a horse. The cysts can cause an interference with the absorption of fluid from the large intestine thereby causing the fluid to be passed in the stool as diarrhea.
Diarrhea also can occur when a large number of larvae all leave their cysts in a relatively short period of time. On rare occasions, this encystation causes enough swelling and inflammation to cause poor absorption of fluid from the large intestine. This syndrome is termed Larval Cyathostminosis and can occur at any age, but is more prevalent in horses between 1 and 4 years of age according to Dr. Nielsen and Dr. Reinemeyer in their book the HANDBOOK of EQUINE PARASITE CONTROL.
By John Byrd, DWM
Problem #1: Colic
Colic just means a horse has pain in its abdomen. There are many causes of this pain and different worms can cause colic. Round worms can cause the pain when a young horse, such as a weanling or yearling, is heavily infected with adult round worms. These young horses seem to become heavily infected at an early age because their immune system does not prevent the larvae from developing into adults. Worms can become very large and completely block the small intestine, in rare cases; they can cause a rupture of the small intestine. This may occur shortly after dewormer is given and all the worms die and the horse tries to pass this entangled mass all at once. This occurs less frequently now because most owners are aware of this problem and deworm their young horses early and often to avoid the problem. Fecal egg counts on young horses over 3-4 months of age can assist an owner in evaluating what the likelihood of having an infection of adult round worm may be.
Any age horse can also show signs of colic from worms. When I graduated from Veterinary school in 1970, large strongyles were the main cause of colic in older horses. Strongylus vulgaris was the one most often responsible. The larvae migrated to the cranial mesenteric artery where they caused severe irritation to the lining of the artery. Blood clots would form in these areas of irritation. These clots would break off and travel to smaller arteries that supplied blood to the areas of the digestive tract. The size of the blood clot would determine how large an area of the intestine would be affected. The size of the affected area would determine generally how severe the colic was. If a large enough area was affected it would prevent the normal peristaltic movement and an impaction of food would occur. Fortunately, most of the time new blood supply would develop and the peristaltic movement resumed before any permanent damage had occurred. However, occasionally larger areas were affected which led to necrosis (death of the intestinal tissue) of the intestine and rupture of the intestine. The only treatment is surgery to remove the section of dead intestine. Fortunately the use of Ivermectin has nearly eliminated Strongyle vulgaris and this cause of colic.
Small strongyles can also cause colic even though they do not migrate through the body as large strongyles do. They only burrow into the intestine wall where they become encysted as part of the normal life cycle. If there are large numbers of these encysted larvae and many of them leave their cysts all at the same time this process may cause enough inflammation to cause some mild signs of colic such as occasionally rolling, restlessness, getting up and down often, not eating, depression listlessness, or slow to no GI sounds. What causes the larvae to stay encysted and then leave the cysts at one time is not well understood. One theory is that there are a large number of adults in the intestine so the larvae wait until there are fewer adults to compete with. Sometimes it appears to be seasonal, in the early spring or late fall when there are many adults in the digestive tract to lay eggs when horses go on pasture in the spring so the contamination is at its highest rate. Another time seems to be when a horse is dewormed and the adults are all killed off.
In the last 7-10 years tapeworms have become more suspected of causing colic. When I graduated from Veterinary School in 1970, when a horse died and a necropsy was done if tapeworms were found in the intestine it was generally noted but it was rare that tapeworms were blamed for causing colic. However, now it is widely accepted that if large numbers of tapeworms are found in the area of the intestine where the small intestine empties into the large intestine the cause of death will be listed as colic. It appears that large numbers of tapeworms that attach to the lining of the intestine can cause enough inflammation and swelling in the area to prevent the normal progression of digestive material and gas through the area. This restriction of movement causes distention of the intestinal wall, which can become great enough to cause colic.
Below is a link to an informative article on the importance of performing fecal egg counts on your horse written by Dr. Craig Reinemeyer. Occasionally I refer to “Equine Parasite Control”, the book he wrote with Dr. Martin K. Nielson because Dr. Craig Reinemeyer is dedicated to improving horses’ health through parasite research. Dr. Reinemeyer is well repsected, considered an expert in the field of Parasitology and enjoys sharing his expertise, in addition he knows a great deal about the most current research.
Craig R. Reinemeyer DVM, PhD, is president of East Tennessee Clinical Research, Inc.; he graduated from the Ohio State University College of Veterinary Medicine in 1976, and spent 5 years in a mixed animal practice before returning to OSU to pursue a PhD in veterinary parasitology. He was a faculty member of the University of Tennessee College of Veterinary Medicine from 1984 to 1998, and served as the President of the American Association of Veterinary Parasitologists from 2003 to 2004. In 1997, Dr. Reinemeyer founded East Tennessee Clinical Research, Inc., an independent business in Knoxville, Tenn., that conducts clinical pharmaceutical research for animal health companies to facilitate the development of new veterinary drugs. ETCR’s efforts have contributed to the approval of several currently marketed anthelmintics for horses, cattle, and pets.
Harmful Effects of Worms
There are many harmful effects caused by a horse having worms. These harmful effects vary according to the species of worms that are present. Unless the worm infection is severe these harmful effects are not generally seen; however, over time much damage can be done to the horse physically.
Dr. Craig R. Reinemeyer and Dr. Martin K. Nielsen state in their book EQUINE PARASITE CONTROL, “Fecal egg counts remain the cornerstone of equine diagnostic parasitology.”
Here is a list of harmful effects that worms can cause in a horse. They may differ depending on the worms present, age of the horse, how heavily infected they are, and duration of infection.
By John Byrd, DVM
How do you know my horse has worms? How do you know you got rid of the worms my horse had? These two questions were commonly asked when I dewormed horses as a general equine veterinarian. My standard response was that the drug companies tell us they work.
When the daily dewormers came on the market many of my clients requested that I get these dewormers for their horses. I often told them I thought it was unnecessary because most of the horses were already being dewormed every 2 months. In addition, 90% of the horses I cared for in southern California were kept in clean box stalls 22 hours a day except when they were being ridden or exercised. I did not see how these horses could have many worms, if any at all. Therefore, I decided to seek the answers to these common questions for myself by doing fecal egg counts before I dewormed my client’s horses.
What I found was that less than 1 out of 20 horses had any eggs in the stool sample to indicate they were infected with adult worms. After consulting with several experts in equine parasitology and recognizing that no one was performing routine fecal egg counts for horse owners, I started Horsemen’s Laboratory to fill this void. I felt owners should have the opportunity to know whether or not their horses had worms rather than just treating them blindly.
For several years now researchers have known that many of the worms that horses have were becoming resistant to the dewormers that were being used to treat them. There also appears to be a link between the over use of these dewormers and the developing resistance. What appears to be occurring is that the dewormers kill most of the worms that are sensitive, leaving only the resistant few to mate with each other. These worms then create more worms that are resistant and soon we have large populations of worms that are now resistant to the dewormer. Performing fecal egg counts can help owners identify if their horse has resistant worms and can also indicate which dewormers an owner should be using.
Stool samples will also indicate which horses are passing the most eggs and therefore identifying the worst contaminators of the pasture. Horses can then be dewormed according to how rapidly they are spreading eggs that will become infective larva on their pasture and in their environment. Research shows that 20% of the horses in a pasture are responsible for 80% of the eggs in a pasture.
Regular stool samples will give horse owners the peace of mind that they have a worm control program that is working to protect their horse from the effects of these parasites. There is no other way of evaluating whether or not you have an effective worm control program. By testing a stool sample before automatically deworming, you may also be helping to slow the development of resistance to dewormers by only deworming when it is necessary. In the long run this may reduce the cost of their worm control program and give owners the confidence that it is truly effective.
HORSEMEN’S LABORATORY has made it affordable and convenient to have fecal egg counts done on your horses. Visit www.horsemenslab.com or call (800) 544-0599 and take advantage of this great service to help protect your horse from worms.
Recently one of our clients at Horsemen’s Laboratory asked about the accuracy of our testing methods. Horsemen’s Laboratory was established in 1991 and since then we have tested over 66,000 samples. In addition, we have sent samples to the University of Illinois, School of Veterinary Medicine Department of Parasitology and to East Tennessee Clinical Research, Inc., a very competent laboratory that does extensive testing and research in the field of parasitology and is owned by Craig R. Reinemeyer, DVM, PhD, Dipl. ACVM to confirm our results. Both of these laboratories placed horses in the same category of egg shedding as Horsemen’s Laboratory, confirming our results.
There are several factors that can affect the testing accuracy, the most common issue occurs when the sample is collected. We instruct clients to completely fill the container we provide and pack the sample firmly. Often we receive samples consisting of only a few small twigs of used hay and a couple of used oats.
There are 2 reasons we need the container filled completely and packed firmly.
The fresher the fecal sample is also improves results. Therefore, we recommend collecting samples on Monday and mailing them immediately. We receive 80-85% of samples within 3-5 days. When samples take longer and are not packed firmly the eggs have a tendency to hatch and we find the larvae swimming in the solution when viewing it on the counting chamber. However, when samples are packed firmly, the eggs have only developed slightly if at all. Occasionally it takes longer for samples to reach Horsemen’s Laboratory and if they are firmly packed the larvae in the eggs again will appear only slightly developed. Samples less tightly packed will have dead larvae floating in solution on the counting chamber, since each egg only produces one larva we just count the larvae.
There are many factors that affect the accuracy of fecal eggs counts, plus the fact that it is not an absolute or precise science. However, it is the best evaluating system we have for determining the presence of intestinal parasites (worms) in live horses. It is also the best method of measuring pasture and environmental contamination that can lead to worm transmission from horse to horse. Therefore, it is the method of choice to evaluate individual horses and herd worm control programs. It is also far better than guessing the effectiveness of your horses’ worm control program.
A client recently asked, “How effective is Diatomaceous Earth as an agent to prevent or control worms in horses?”
Here’s what Horsemen’s Laboratory has found through performing fecal egg counts on horses that are being fed Diatomaceous Earth. In horses that are high shedders, the egg count is often fairly high, 500 strongyle eggs/gm of stool or more. Owners often repeat the test after feeding more Diatomaceous Earth and the results are most often very similar to the first sample. For owners that have a closed herd or only have one horse in a pasture and feeds Diatomaceous Earth we often find egg counts to be very low or negative (no worm eggs found on the counting chamber). These same owners often comment that they clean their horse’s pastures every day or two. Cleaning pastures and removing the eggs before they hatch and become infective larvae has been found to be one of the best practices in the control of worms. Horsemen’s Laboratory has also found that horses that spend most of their time in pastures where the owner cleans on a daily schedule and do not feed Diatomaceous Earth are routinely low shedders to negative and often remain in that category for long periods of time.
Horsemen’s Laboratory does not have hard evidence of the effectiveness of Diatomaceous Earth. It may slow how fast the population of worms multiplies in horses, but it does not appear to completely control worms in horses. That being said, there seems to be many routines and schedules for feeding Diatomaceous Earth and the effectiveness may depend on what routine, schedule and amount that is fed.
This is a summary of an article that was written by Dr. C. R. Reinemeyer and Dr. M. K. Nielsen and was published in EQUINE VETERINARY EDUCATION. This article reviews essential features of the biology, epidemiology, pathology, diagnosis, and control of Oxyuris equi (pinworm) infections, and describes the current status of recent biological adaptations. You may Google Review of the Biology and Control of Oxyuris equi, in order to view the entire article.
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