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2004 Fall/Winter 


The Scoop on Poop

We all do it. We all deworm our horses every 2-3 months with paste dewormers; we rotate dewormers so parasites don’t develop resistance, and we know the importance of deworming. However, do we really know what we’re up against? Do we know why we’re rotating dewormers and are we doing it effectively? Hopefully, after this article you will have more of an understanding of the reasons for your faithful deworming program.

There are more than 150 species of internal parasites that can infect horses. However, there are more common and troublesome ones that we deal with most of the time that include: large strongyles (often called bloodworms), small strongyles, ascarids (roundworms), tapeworms, lungworms, pinworms, bots, threadworms. The first four (large and small strongyles, roundworms and tapeworms) are the most important as far as the health of your horse. Most of these parasites go through similar life cycles involving eggs, larvae (immature worms) and adult worms. The eggs or larvae are deposited onto the ground through the infected horse’s manure. They develop in the environment and eventually are swallowed while the horse is grazing in the pasture or eating off the ground and then the larvae will mature within the horse’s GI tract. The larvae of certain species of parasites will likewise migrate out of the intestine into other tissue or organs before returning to the intestine to mature into adults who will then produce eggs and start the cycle back over again.

Clinical signs of parasitism can vary greatly from horse to horse. Horses massively infected with parasites can have clinical signs of it or can sometimes look relatively normal and healthy. Common clinical signs of parasites can include dull hair coat, lethargy, decreased stamina, loss of body condition, slowed growth in young horses, pot belly (especially in young foals), recurrent colic, diarrhea, etc… When you likewise consider that some parasites make larval migrations through the body before going back to the GI tract, you can also see chronic coughs with lung migration or liver inflammation with liver migration. Constant rubbing of the tail head can also be a sign of pinworm infestation.

So let’s talk more about these small culprits that are our topic of discussion. LARGE STRONGYLES or as they used to be called “bloodworms” got this name because as larvae they penetrate the lining of the bowel and can migrate along the blood vessels that supply blood to the intestines as well as the fact that they are “blood suckers”. Large strongyles are among the most destructive parasites of the horse. During this larval migration, as they’re cruising around in your horse’s GI blood vessels, they continue to grow and eventually occlude and destroy the blood vessels. The larvae are then free to undergo a final molt and then enter back into the GI tract where they begin producing eggs again. You can then see if there is a massive infection of large strongyle larvae, and if too many blood vessels are destroyed, they could effectively destroy a section of your horse’s GI tract due to lack of blood supply, and your horse would develop severe colic which would require surgery for survival. Other types of large strongyle larvae make migrations through the liver and pancreas, but they’re not as destructive and usually don’t cause any obvious clinical signs. Due to their voracious blood sucking nature they can show most of the previously discussed clinical signs as well as low red blood cells (anemia). Thankfully these parasites are easily controlled with deworming programs. Likewise, the horse fortunately has a very good checks and balance system with their GI blood supply which means that they have a lot of blood vessels supplying the same area. Therefore, if one vessel is destroyed there is usually another to help take up the slack. Also, if you deworm at appropriate intervals, even if blood vessels are almost completely occluded and cut off, once you kill the larvae the blood vessels often bounce back and start working effectively again.

SMALL STRONGYLES have yet another trick up their sleeve. Their larvae do not migrate through tissues; however, instead of completing a normal life cycle they sometimes burrow into the lining of the intestine and become dormant or “encyst” for several months. While they are hiding out in these cysts, most dewormers can’t affect them. However, Quest® and a Panacur PowerPac® have both been labeled for treating this stage, so please keep that in mind. Often times we see clinical colic in relation to these encysted small strongyle larvae in late winter or early spring when they tend to come out of their cysts in this area. So picture this if you will…..you have several hundred or thousand small strongyle larvae hiding out in your horse’s intestinal lining, minding their own business when some unknown stimulus (whether it be that the weather is improving and it would be perfect time to contaminate your pasture, or that your mare is getting ready to foal and it would be a perfect time to contaminate your foal) tells them all to hatch and they all “rip” out of their cyst and “rip” through your horse’s intestinal lining to get to the intestine. Ouch is right. That pain and damage to the intestine can cause massive inflammation, colic, and diarrhea.

ASCARIDS or ROUNDWORMS are most often a problem in foals, weanlings and yearlings. Adult horses often develop a resistance to these parasites and it is for this reason it is usually not clinically a problem in adults. These are the worms that I usually get calls about because it’s one of the only parasites in a horse that you can easily see. They can be several inches long and about the diameter of a pencil and really freak horse owners out, especially if they’re still moving when they come out. The larval stage of these parasites has yet another way to wreak havoc on your horse. Their migration makes a trip through the wall of the intestines to the liver, through the caudal vena cava to the heart and then to the lungs of your young horse where it can cause pneumonia, coughing, nasal discharge, etc… As it matures it is literally “coughed” up to the mouth where it is again swallowed and gets back into the GI tract. And then once they mature and start developing eggs, just one female roundworm is capable of laying 200,000 eggs per day. WOW!! Likewise, due to the sheer size of these parasites, a massive infection of them can cause young horses to look pot bellied. So picture this if you will….you have a foal massively infected with roundworms and you deworm your foal to kill the parasites. You now have a large amount of huge, dead parasites attempting to exit out all at once and sometimes they can cause an impaction and a colic that could require surgery. I’ve seen heavily infected foals fill buckets with dead roundworms (not a lovely picture I can assure you). It is for this reason I usually recommend using a half a dose of a dewormer 2-3 times in 1-2 week intervals in a heavily infected foal to help reduce the risk of too many worms dying at once.

TAPEWORMS are the new, vogue parasite. For a long time this parasite was not believed to be very significant in the grand scheme of things. However, recent studies have indicated that tapeworms can be more problematic then originally thought. One theory suggests that since we are taking better care of clearing the horses of the large and small strongyles, we are allowing tapeworms to establish a better foothold since most of the dewormers do not affect tapeworms. To contract tapeworms, horses ingest a free-living mite containing the tapeworm larvae while grazing. These mites can live for up to 18 months and once ingested, the larvae emerge from the mites and then attach to the horse’s small intestine or cecum and mature to adults. It takes 4-6 weeks from ingestion to when the adults are passing segments containing eggs in the manure. Large numbers of tapeworms create problems by causing ulceration in the large intestine and cecum and in turn causing colic and intestinal blockage. Studies have likewise shown that tapeworm infestation can make horses eight times more likely to experience gas colic than uninfected animals.

There are two other parasites that do not cause as severe of clinical disease but are worth noting nonetheless. PINWORMS are little parasites that live in the colon and rectum of the horse. They “peek” out of the horse’s anus and lay eggs around the rectum and go back in to live another day. These eggs make the horse extremely itchy and they begin rubbing and can cause hair loss and inflammation on the tail head. BOTS are another parasite that are noteworthy. If you have ever seen small orange spots on your horse’s lower limbs or ventral abdomen, then you have seen bot eggs. Bot flies (resembling a house fly on steroids) lay eggs on your horse’s limbs; these eggs will get consumed when your horse rubs his legs with his mouth; they then mature in the horse’s stomach for almost a year and then pass out in the feces and pupate in the soil where it will emerge as an adult fly again. It doesn’t cause much damage to the horse but a lot of people ask me what the little orange/yellow spots are on the horses that can’t be groomed off. You usually have to literally cut or shave them off.

So now that you know a bit about what we’re trying to control, let’s talk about some management issues. One of the best things that can be done is pasture management. In the wild, horses will eat in an area and then move on thus helping to break the parasite life cycle because they won’t consume more eggs from the infected manure. However, domestic horses do not have that luxury. They are confined to just ONE area and they cannot move on to another. However, horses themselves do lend a hand in keeping free of internal parasites while grazing. They will, whenever possible, graze on the “lawn” of the pasture rather than the “roughs”. Most of you have seen this if you have green pastures, there are sections of your pasture that they tend to poop in with taller grass and they don’t usually eat in that area. The lawns are uncontaminated areas and the roughs are areas containing piles of manure. As the weather cools, however, the horses will graze closer and closer to the roughs since the grass is becoming scarce and in the process could wind up consuming copious quantities of infective larvae. One way to rectify the problem is to clean your pasture on a regular basis; the best option is to clean the manure from the pastures twice a week.

Another misconception is survival of the parasite eggs or larvae stages. It is a common misunderstanding that your pasture will get “cleared out” over the winter since all the parasites will freeze to death. That is DEFINITELY not the case. For example, strongyles once arriving to the third stage are resistant to cold and desiccation and can survive on pasture through a northern winter or in stored dry hay for many months. Therefore, any pasture that has held a horse within a year can be assumed to be contaminated with strongyle infected larvae. Fortunately, the safest time for a horse to be on pasture, from a parasite infestation point of view is the same time the grass is richest and most edible---during the warm summer months. The hotter the weather, the less likely parasite eggs will survive when passed with the manure. And this is the time that the “lawns” and “roughs” work the best because there is plenty of grass available in the lawns. Some will advocate that you should attempt to dry out the larvae before they reach the desiccation-resistant third stage. You can do this by scattering droppings with tractor and harrow or a lawnmower. However, when you consider that your horse is attempting to keep his “lawns” and “roughs” separate, spreading out the feces could inadvertently infect the ENTIRE pasture and then when the weather cooled again there would be more chance for contamination. Therefore, only drag a pasture with a harrow if it is currently being unused. If manure needs to be spread onto pasture then it should be composted first to allow temperatures to rise to the point parasite eggs are destroyed.

Likewise, roundworms can remain infective in the soil for many years. In fact, a viable egg can survive for up to a decade. These eggs accumulate as a growing reservoir of infection in polluted soils. In other words, one year’s foal crop can leave behind a deadly legacy of potential infestation for the next year’s foal crop. These eggs have a very thick, protective, sticky shell covering them that allows them to stick to almost anything… stall walls, mangers, water buckets…even to the teats and udder of broodmares waiting for a foal to be born. Thorough cleaning of the foaling stall (pressure washer) as well as the mare’s udder and teats can be well worth it in contaminated situations. As discussed earlier, adults tend to develop resistance to this parasite, so most of your emphasis should be on the protection of your young stock.

The most common dewormers include ivermectins (i-ver-meck-tin), pyrantel (pie-ran-tell), moxidectin (mocks-e-deck-tin), fenbendazole (fen-ben-duh-zoll), oxibendazole (oxy-ben-duh-zoll) and praziquantel (pra-zee-kwan-tell). Now I’m talking active ingredients or actual drug names, not the manufacturer’s name that they call it. I would rather you get used to using the actual drug name because it will be easier to know what you’re using. I have had clients tell me that they are rotating dewormers and the last three dewormers they have used were Eqvalan®, Ivercide® and Zimectrin® (all ivermectin products). It is also important to realize what each active ingredient best covers.

However, rotation of dewormers is now coming under scrutiny. And even recommendations that I have made recently may need to be somewhat abridged. Originally rotation was due to the fact that most of the dewormers weren’t very broad spectrum (didn’t kill all the types of worms) so you rotated to make sure you got all the different types. NOW, the reason that rotation is deemed important is to help prevent parasites from developing resistance to the dewormers. The theory is this….if you keep throwing something new at them they won’t develop a strain of parasite that is resistant to one particular class of dewormers. But they’re now showing that if the rotation occurs too frequently we may end up not only developing resistance, but it may be to multiple dewormers. Slower rotation of dewormers, e.g. on a yearly basis, has been recommended to delay the parasite’s natural selection towards resistance. It has worked well in the past for cows and goats, but there has not been a lot of data confirming it will work as well in horses since they have a different GI system. But if your small strongyles have developed any type of resistance at all to a particular dewormer, then we could be risking the health of our horses by deworming with only one type of dewormer all year. So in this case we are still at a loss.

Another route certain owners (including myself) employ is the daily dewormer regiment. In this theory a daily dose of the pyrantel will help prevent larval infestation of the parasites and your horse will not develop an adult infection. But again, this theory goes against some of the experts who believe that parasite resistance will develop from such therapy. A strong reason to use this product has been some of the programs available such as the Preventicare Program which will help cover the cost of a colic surgery if you keep your horse on their daily dewormer product and twice annual oral dewormer. It is a good program and I’ve had horses maintain a healthy protection against parasites with it….however the United States (where these programs are most prevalent) show more pyrantel resistance to parasites than other countries. It is also important to remember that this medication will not clear existing infections or bots, so they should be regularly dewormed with a paste twice a year. There has been proof, as well, that this medication on a daily basis after clearing an infection with a praziquantel paste can help prevent infection with tapeworms.

Another route that some experts are advising is more frequent evaluations of your parasite program. In other words, evaluating your parasite loads PRIOR to deworming your horses and determining if there is a need for dewormer at that particular time. Twice annual fecal examinations are currently being recommended to help evaluate your deworming protocol. If you are worried about parasite resistance to a particular class of dewormers, then a fecal examination should be done prior to and then around 1-2 weeks after the deworming to evaluate its effectiveness. After a time, you may start to implement fecal examinations INSTEAD of deworming and evaluate which of your horses actually need deworming at that time. Keep in mind, however, that tapeworms, bots and pinworms will not show up on fecal examinations. Likewise, encysted larvae that are not producing any eggs could show a negative fecal examination and then when they hatch out, they can start producing massive amounts of eggs. However, the parasites that aren’t readily seen on fecal examinations can be taken care of with one dose of Quest Plus®.

So in the end, our best intervention is prevention through sound pasture management skills and control. Notice I do not mention elimination. In the long run, a low or mild level of infection can actually help your horse maintain an acquired immunity to the parasites. There are some good rules of thumb that can help you with your quest of parasite control:

  1. Deworm your pregnant mares prior to and after foaling to help prevent transmission to your young foal. Diligently clean the foaling stall and the mare’s teats / udder prior to foaling as well, especially in known contaminated areas.
  2. Keep foals away from older horses to help prevent cross contamination.
  3. Deworm with a larvicide (Panacur PowerPac®, Quest®, Quest Plus®, Combocare®) to any new horses on your farm. Barns should make this a requirement for any new boarders coming into their facility to help remove as much of the total worm burden as possible.
  4. Routine fecal examinations should become part of your deworming program. If you have multiple horses, then arbitrarily pick a few to have evaluated. If you have several different age brackets, pick a horse from each age bracket. If you have different pastures with different horses in each, pick at least one horse from each pasture for evaluation. New horses should be evaluated prior to and after deworming to evaluate for effectiveness and to check for resistance.
  5. Routinely clean your pastures and turn outs at least twice a week, especially in the early spring and late fall when the chances of contamination are the highest.
  6. If possible, keep the number of horses per acre to a minimum to help prevent overgrazing and reduce pasture contamination with eggs and larvae.
  7. Use a feeder for hay and grain rather than feeding on the ground.
  8. Remove bot eggs regularly from your horse’s hair coat.

I hope this article has given you some insight on the proper techniques for the best parasite control program. If you have any questions or would like to discuss a better deworming program for your horses or barn…please contact us at 219-313-8628 or nuestdvm@greenerpasturesvet.com. And that my friends... is the scoop on poop.

Taking Horses Home

I received this great idea for a newsletter article from one of my clients who recently took his horse home from a boarding situation. He had stated that “even after owning horses for over 20 years, it was still a might scary being [the horse’s] sole provider”. Likewise, he thought there were a lot of aspects he had not considered or addressed. So for all of you out there who are just getting a horse for the first time or considering taking your boarded horse home for the first time…here’s a few points to consider:

1. Feed. Yes, you will have to feed your horse. And yes, you will have to make sure you purchase enough hay WHEN hay is available. This will consist of you calculating out how much your horse eats per day and multiplying it by the number of days until the next available cutting of hay. Likewise, you will need a way to store that hay so it is protected from the elements. It is also a good idea to get associated with a hay distributor that will be a consistent source of hay for you for years to come.

2. Pasture. There are several points to consider here. First, did your horse have access to pasture at the previous place? If not, then throwing him out on green, lush grasses will not be the best to do. If he did have pasture, was the pasture similar to what you have now? If he came off a pasture that looks like outdoor carpeting (overgrazed) and you’re throwing him out on over your ankle lush pasture…the same problems arise. Also, have you evaluated your pasture for poisonous plants or trees that could affect your horse? Is your fencing similar to what he is used to and is it safe? Will you be able to manage your pasture (see previous article) to help prevent parasite contamination? You need to consider pasture mates as well. Any time new horses are introduced to one another in a pasture situation, there may be conflict and you need to be ready to deal with it.

3. Barn safety. You may not think about the safety of barns when you’ve boarded your horse, because hopefully your boarding barn owner has thought of it already. Look around the barn…Are there exposed wires your horse can reach? Any nails sticking out in the stall? Are the bars on the stall closely spaced enough so horses cannot get their hooves caught in them? Do you have a way to keep water unfrozen in the winter? Access to adequate light if your horse has a problem in the night (really great for veterinarians)?

4. Feeding regiment. Ask the previous care giver about the horse’s feeding regime. When is the horse fed? How is he fed? e.g. hay first, then grain. What type of grain is he getting fed? You should not change feed quickly in horses and it would be best to wean him over to new hay and grain slowly.

5. Deworming. Ask the previous care giver when his last deworming was performed and what product it was. Some boarding barns do this on their own, and owners are unaware of their horse’s deworming program. See previous article for more information.

6. Water. They need to have a good source of water and during the summer it should be cleaned regularly (every 10 days will help control your mosquito population) and in the winter you will need to make sure it doesn’t freeze.

7. Signs of Illness. If you are not sure when to call a veterinarian, you may need a refresher course on some clinical signs of illness. Signs of colic can include pawing, rolling, laying down, turning down feed, etc… Swollen eyes or severe squinting, discolored eyes, non-weight bearing lameness, breathing problems with flared nostrils, widespread hair loss, are all signs that should include consultation with your veterinarian.

8. Preventative Care. If your boarding barn or the previous owner has a regular routine for veterinarian care or farrier care…do not assume that the same farrier and veterinarian will be able to attend to where the horse is moving. If you are moving a significant distance from the horse’s previous location you may not be within the normal coverage of care for these individuals. BEFORE you get your horse home you should check with your desired farrier and veterinarian to verify that you will be able to get into a routine care program with them. If they are not available, you should make sure you can get one out before you try at midnight when you have an emergency.

I hope these give some points to think about. If any of you have taken your horse home and had something else pop up that you hadn’t considered….let me know. Maybe we’ll make this a two-part article. Contact me at 219-313-8628 or nuestdvm@greenerpasturesvet.com.

Did You Know?

There have been recent advances in biologic control of parasites. There have been studies using a fungus that traps and destroys developing larvae in feces, thereby reducing environmental contamination with infective larvae. These are the nasty larvae that contaminate our pastures. Additional research still needs to be performed before it can become a viable alternative, but they hope technology such as this may offer some hope in reducing the frequency of deworming and subsequent dewormer resistance. This type of technology will help insure the prolonged useful life of the available drugs.

Christmas Vacation

Just to let you know, I will be taking a vacation over the Christmas Holiday. Our clinic will be closed to appointments and emergencies Thursday, December 16th through Thursday, December 23rd. My technician, Mandy, will likewise not be available. I will have the phone numbers of area veterinarians on my phone message if you need emergency care. I hope you and your family (including all that sleep in stalls) have a wonderful holiday season.

Cowboy Christmas
May your horses never colic
Your grass always be green
Hoof picks always handy
And blankets always clean

Stirrups always long enough
Brushes clean and dry
Clippers blades that work like new
And hay stacked rafter high

Boots and saddle broken in
and fitting like a glove
Your trail rides nice and sunny
With no showers from above

May you never have to walk back home
But always be astraddle
Your favorite horse, and of course
In your favorite saddle

May you always use good judgement
And not let pride prevail
When climbing in the saddle
Of the local horse from hell

May your papers be in order
Your vaccines never fail
Your trailer tires always hold air
And your horse “stay on the rail”

May all your ribbons turn out blue
Your trophies always tall
Your winnings always be real big
Your entry fees real small

May your water buckets never freeze
Your cinch be always tight
Merry Christmas to all you cowboys
and to all of you a good night.