What others are saying about Horse and Donkey Worms and Worming.
This one will save your horse's life.
Of all the equine related books available on every possible subject, as far as I am concerned, none are more important than one that will save your horses life. All supported by scientific research and end notes. So many equine books are nothing but someone's opinion, not supported by research or facts. This one is! Worms kill horses and the traditional means of deworming is not working. She talks about all the myths with deworming.... using quest with foals and horses, when to deworm depending on your climate and location, the myth about fecal counts being a good way to know whether horses have worms (wrong!), the myth about copper and many of the natural/herbal dewormers that not only don't work but some are toxic, rotation makes worms immune to the dewormers. Horses still die and they have been on regular schedules of dewormer.... you know the vet always asks, 'has this horse been wormed recently?' The answer is always yes by good horse owners and they had zero worm count in fecals, the horse dies and the autopsy's shows the horse is full of worms.
If you have a horse, if you are thinking of getting a horse, then you need to read this book and get smart on this killer. Horses are dying right now as we speak because of ignorance and because horse owners are listening to ill advised people on how to deworm their horse. The horses suffer because of our ignorance. Pick up this book and read it for your horse, you'll be amazed what you will learn. I'll be changing the way I deworm as of right now.
(Celeita Kramer
Owner, Crossed Sabers Stable
President/Executive Director, The Mountain State Horse School and Second Wind Adoption Program, Inc.)
Most Important Horse book ever
"If there is only ever one horse related book you ever buy or read, make sure it is Horse and Donkey Worms and Worming by Dr. Ann Nyland.
I cannot believe my ignorance of the RIGHT way to approach worming horses. Ann lays it out simply and easily.
Forget what you ever thought you knew about rotational worming and read this book!!!
I was seriously shocked by how wrong I had it all and I consider myself reasonably well educated and informed on horse health issues.
Learning about the terrible dangers of encysted small strongyles in otherwise healthy looking horses was quite frightening.
(Jen Green - Flying Circus Endurance Stables - Australia)
Horse and Donkey Worms and Worming
by
Dr. A. Nyland
SMASHWORDS EDITION
* * * * *
PUBLISHED BY:
Dr. A. Nyland on Smashwords
Discover other titles by Dr. A. Nyland at Smashwords.com
This book is available in print at most online retailers.
Horse and Donkey Worms and Worming
Copyright 2010 by Dr. A. Nyland
Smashwords Edition, License Notes
This ebook is licensed for your personal enjoyment only. This ebook may not be re-sold or given away to other people. If you would like to share this book with another person, please purchase an additional copy for each person with whom you share it. If you are reading this book and did not purchase it, or it was not purchased for your use only, then you should return to Smashwords.com and purchase your own copy. Thank you for respecting the author's work.
Cover: Arabian mare Seven Seas La Serenissima. Owned by the author.
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“Most veterinarians continue to recommend anthelmintic treatment programs for horses that are based on knowledge and concepts that are 30-40 years old.”
(M.K. Nielsen, R.M. Kaplan, “Evidence-Based Equine Parasitology – It Ain’t the 60s Anymore,” Proceedings des 36èmes Journées Annuelles l’Association Vétérinaire Equine Française, 2008 - Reims, France)
“Rotation is no longer an option.”
(C.R. Reinemeyer, "Controlling Strongyle Parasites of Horses: A Mandate for Change," Proceedings of the 55th Annual Convention of the American Association of Equine Practitioners, 2009.)
“The playing field has changed drastically.”
(C.R. Reinemeyer, "Controlling Strongyle Parasites of Horses: A Mandate for Change," Proceedings of the 55th Annual Convention of the American Association of Equine Practitioners, 2009.)
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Table of Contents
Chapter 1. Introduction
Chapter 2. Table of chemical dewormers
Chapter 3. Large strongyles: Strongylus vulgaris
Chapter 4. Large strongyles: Strongylus edentatus and Strongylus equinus
Chapter 5. Roundworms (ascarids/Parascaris equorum)
Chapter 6. Bots (Gasterophilus intestinalis, Gasterophilus haemorrhoidalis, Gasterophilus nasalis)
Chapter 7. Small strongyles (cyathostomes)
Chapter 8. Tapeworms
Chapter 9. Lungworms (Dictyocaulus arnfieldi)
Chapter 10. Pinworms (Oxyuris equi)
Chapter 11. Stomach worm (Trichostrongylus axei)
Chapter 12. Warbles
Chapter 13. Threadworm (Strongyloides westeri)
Chapter 14. Liver fluke (Fasciola hepatica)
Chapter 15. Chemical dewormers
Chapter 16. Herbal and “natural” – not for horses!
Chapter 17. Fecal Egg Counts
Chapter 18. Foals
Chapter 19. Resistance and Rotation
Chapter 20. Prevention
Chapter 21. When to Worm and What With?
Chapter 22. When to worm according to your climate
Chapter 23. Appendix: Table of Worming products
Chapter 24. Endnotes
Chapter 25. Bibliography
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In the 1960s, the dangerous worm was the large strongyle (Strongylus vulgaris), and worming treatment in the 1980s and 1990s targeted this worm. Today, the problem worm is the small strongyle (cyathostome), yet the vast majority of advice given today for worming horses is still aimed at the old regimens suited for eradicating the large strongyle (which by the way is no longer the problem). Today, the worming program should be aimed at the cyathostome – it is not the only worm of course, but it should be the focus of today’s worming programs.
The old idea of rotation still lingers on from the early days where it was first put forward in 1966. (1) Rotation is no longer advocated by equine parasitologists.
In fact, misinformation about horse and donkey worms is all over the net, from natural therapists to, more so, chemical companies. Horses have died because of this misinformation.
It is common to find statements in advertising and about dewormers such as: “100% effective against all worms of horses and bots.”
“(Non moxidectin, Non fenbendazole product) safely and effectively rids horses of all major internal parasites, including tapeworms, in a single dose.”
“(Chemical) eliminates all common horse worms and bots.”
“(Non moxidectin, Non fenbendazole product) has the capacity to treat all common types of parasitic worms (including tapeworms) and bots.”
“(Non moxidectin, Non fenbendazole product) has the best combined efficacy and the broadest spectrum of activity of any wormer.”
“(Product) completely protects young horses from ascarids, as well as all other worms.”
The above statements are misleading. There is no one product on the market that can be 100% effective against all worms. In fact, only moxidectin (for example, in Quest/ Equest and Farnam ComboCare) at a single dose, and fenbendazole (for example, in Panacur 100) at a double dose (2) for 5 consecutive days, are effective against some stages of encysted cyathostomes (small strongyles) – more on this later. Yet internet advertising for one product based on ivermectin even goes so far as to state, “There is no known resistance.” However, resistance to ivermectin has been widely reported. (3)
Do not make the mistake of believing if something is said about a product, it must be true. I reported a false claim about dewormers to the regulatory government body in my country. I received a letter from them saying they would look into it, but over a year later, the same company is still making the same false claims.
I read an online ad for a major herbal wormer for horses which stated, “Cinnamon, for example is known for its repelling properties, especially effective against roundworm, pinworm and threadworm.” However, there is no scientific evidence whatsoever to support this claim. Cinnamon has been shown to be somewhat effective against a certain parasite in the Tiger Puffer fish, (4) but that’s it. Even the recent (2007) veterinary herbal medicine book, Veterinary Herbal Medicine, does not list deworming under the uses for cinnamon. (5)
Do not let your dogs near horse wormers, as some can cause all sorts of nasty symptoms such as pupil dilation, vomiting, convulsions, tremors, coma, respiratory failure, (6) even death. (7) If you have a dog, remove any wormer that falls on the ground after you have wormed your horse or donkey. Also, do not worm your horse near any fish ponds, as many horse wormers are also toxic to fish, turtles and tortoises. Also keep cats away from wormers.
It is also important to make sure the horse or donkey receives the full dose for its weight, as underdosing is a contributing factor to resistance. However, very special care needs to be taken to avoid overdosing donkeys and miniature equines.
On the subject of donkeys and miniature equines, these are just as susceptible as horses to worms. (8) For example, a study on 150 French donkeys found that 75.9% of them had cyathostomes. (9)
Also, some people use sheep drench for their horses in an attempt to save money – do not do this!
Signs of Worm Infestation
A horse or donkey can be looking fat, shiny and healthy and be full of worms. Never go by appearance!
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Chapter 2. Table of chemical dewormers
The four main classes of anthelmintics used in horses and donkeys
1) Benzimidazoles
Fenbendazole
Oxibendazole
Mebendazole
2) Tetrahydropyrimidines
Pyrantel pamoate
Pyrantel tartrate
3) Macrocyclic lactones:
Avermectins
Ivermectin, abamectin, doramectin, eprinomectin, and selamectin
Milbemycins
Moxidectin and milbemycin oxime
4) Isoquinoline-pyrozines
Praziquantel
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Chapter 3. Large strongyles: Strongylus vulgaris
Ivermectin will kill both adult and immature stages of Strongylus vulgaris, so it’s unusual to find problems with these worms anymore. This is just as well, as they like to eat away at the cecum and the colon and like to migrate and cause lots of damage (10) such as thromboembolic colic and verminous arteritis. (11) Prior to the widespread use of ivermectin, Strongylus vulgaris used to be a common cause of colic. They caused inflammation and architectural changes in the cranial mesenteric artery which in turn caused blockages, and this led to colic in varying degrees and sometimes to death. (12)
After the horse eats the Strongylus vulgaris larvae, L3s leave their previous developmental stage (13) in the small intestine, and infiltrate the mucosa (intestinal mucous membrane) and become L4s only 7 days after infection. These L4s infiltrate submucosal arteries and take off along the endothelium and reach the cecal and colic arteries 14 days after infection. Then they head off and arrive at the root of the cranial mesenteric artery 21 days after infection. After they develop for 3 to 4 months, the larvae go back to the intestinal wall via the lumen of arteries. Nodules are formed around the L5s and this happens mainly in the cecum and colon and walls. When these nodules rupture, the young adult parasites are released into the lumen of the intestine. They mature in a further 6 to 8 weeks.
Large strongyles are easy to control as they have a long Pre-Patent Period (that is, the time between infection and the first appearance of eggs) of at least 6 months, which means that once an effective wormer is given on one occasion, a whole pre-patent period needs to run its course before eggs can infect the environment.
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Chapter 4. Large strongyles: Strongylus edentatus and Strongylus equinus
The other two species of Strongylus in the horse are Strongylus edentatus and Strongylus equinus. Larvae of Strongylus edentatus enter the gut wall, go through blood vessels and head off to the liver where they stay for about 6 weeks. They leave there and turn into immature adults about 13 to 15 weeks after infection, and then they head back to the large intestine. They mature in the large intestine and the pre-patent period is approximately 11 months. (14)
Larvae of Strongylus equinus enter the wall of the small intestine, cecum and colon. Next they migrate to the liver where they stay for around 6 weeks, and then they head off to the pancreas on their way to the gastrointestinal tract. About 13 to 15 weeks after infection, the L5s actually penetrate the gut wall and enter the lumen of the large intestine by forming nodules. (15) The pre-patent period is approximately 9 months.
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Chapter 5. Roundworms (ascarids/Parascaris equorum)
Roundworms (ascarids/Parascaris equorum) can be nasty in the foal – they can migrate and cause respiratory disease, and they can also migrate to the liver just one day after being eaten by the foal. When on the ground (as opposed to in the horse) they are very, very hard to kill, even with the most determined of disinfectants, and can build up in the horse’s environment and stay there for years – in paddocks, stables, anywhere the horse hangs out. (16) You could clean up manure all day long and it wouldn’t make any difference with these! What makes it worse is that the females usually lay millions of eggs. (17) Bear in mind that these horrible creatures have been found in older horses too. (18)
Moxidectin (a second-generation macrocyclic lactone of the milbemycin family), ivermectin, fenbendazole, and pyrantel are effective against roundworms. Products containing these compounds all have a registered claim against adults and L4 stages, although only ivermectin has a claim for L3 stages in most European countries.
Fecal Egg Counts are too late to be of any help, as tissue inflammation will already have occurred by the time these eggs show up. However, that said, they can be of use in timing the treating. Parasitologist M.J. Murray suggests administering a dewormer when the foal is 2 months of age and then performing Fecal Egg Count 2 months later. If the eggs are still present, deworm again. (19)
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Chapter 6. Bots (Gasterophilus intestinalis, Gasterophilus haemorrhoidalis, Gasterophilus nasalis)
Bots (Gasterophilus intestinalis) generally aren’t as nasty as the others. We have all seen bot eggs on the horse’s legs and those nasty bot flies that look and sound like bees and are hard to catch!
The horse eats them and they hatch in the horse’s mouth, and set up residence for there for about a month. Then they turn into what is called “2nd instar larvae” and the horse swallows them. They attach to the stomach, and after having a good time in the horse for about eight to ten months, the third instar larvae detach and come out in the horse’s droppings. They will then pupate there and then emerge as flies three to four weeks later, and then lay eggs, and so the cycle continues. (20) A bot is the larval stage of the bot fly.
Besides the common bot, Gasterophilus intestinalis, there are two other species of horse bots, Gasterophilus haemorrhoidalis, and Gasterophilus nasalis. They are pretty much the same, the only difference being that Gasterophilus intestinalis eggs attach to the hair on the legs and shoulders, whereas the eggs of Gasterophilus haemorrhoidalis attach to the hairs of the lip, and the eggs of Gasterophilus nasalis attach to hairs under the lower jaw. The other difference is that while the third instar larvae of Gasterophilus intestinalis and Gasterophilus haemorrhoidalis attach to the stomach, the third instar larvae of Gasterophilus nasalis attach to the intestine.
Bots are found all over the world. Their eggs can be removed from the legs with a bot knife (throw them out, don’t let them fall on the ground!), or by scrubbing hard with warm water. The avermectin class of chemicals will dispose of them.
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Chapter 7. Small strongyles (cyathostomes)
Consider the life cycle of the small strongyles also called cyathostomes. The adult small strongyle lays eggs which are passed in the horse’s droppings. Favorable conditions are humidity about 80%, and optimum temperature at 77 degrees F (25 degrees C). Under these conditions, the eggs passed in the manure will develop to L1 larvae within a few days. (21) With temperatures averaging 55 degrees F (12 degrees C), it may take weeks or months for an egg to progress to the L3 stage. No successful larvae development occurs at less than 42 degrees F (5 degrees C) or more than 100 degrees F (38 degrees C). (22) Larvae actually die at temperatures over 90 degrees F (32 degrees C), but can tolerate a heavy frost or freezing. (23)
The horse eats the L3 (third stage larvae). The L3s go into the lining of the horse’s colon - *sometimes as QUICKLY as 6 HOURS* - and form a cyst. This is why they are called at that point encysted small strongyles. The wormer Equest/Quest –name depending on your country - kills many of these L3s. (24)
These are now called early L3 larvae (EL3). The EL3 larvae encyst in the mucosa or sub-mucosa of the intestine. The EL3 become hypobiotic (become inhibited L3 or IL3) and they can stay like this from anything to a few months to a few years. (25) In the northern hemisphere in northern temperate climates this happens in the winter, but in the southern temperate climates with hot summers and mild winters this happens in the summer.
75% of these L3s are actually EL3 (early third stage larvae) and some are inhibited. Now, moxidectin, the chemical in Equest/Quest (different names in different countries) may not kill all EL3s in 1 dose. The registered claim of Equest/Quest and ComboCare shows that they are currently the only wormers effective as a single dose against encysted stages of small strongyles, developing stages (L), late encysted stages (LL3/EL4) and aid in control of early encysted stages (EL3) including inhibited larvae (greater than 90% effective.) (26)
Note the “aids in control.” Moxidectin has not been demonstrated to be completely effective against EL3. Fenbendazole (but resistance has been demonstrated) (27) has been shown to be effective against inhibited EL3s if given for 5 consecutive days at a dose of 10 mg per 1 kg horse bodyweight (28) - this is, for example, is the recommended dose rate for Australian product Panacur 100 but in some countries such as the USA is double the recommended dose rate.
In the USA the registered claim for Panacur and Safe-Guard is, “For treatment of encysted mucosal cyathostome (small strongyle) larvae including hypobiotic early third stage, late third stage and fourth stage larvae at 10 mg/kg/day for 5 consecutive days.” (29) It also states, “Fenbendazole administered orally at 10 mg/kg for 5 consecutive days to horses/ponies with naturally acquired cyathostome infection is safe and effective.”
Now, NO OTHER HORSE WORMER (but moxidectin in a single dose or fenbendazole for 5 consecutive days at a certain dose rate) can affect these encysted small strongyles! (30) It won’t even give them a headache! You could worm your horse with standard wormers until you were blue in the face, and it would do nothing against encysted small strongyles! (31)
Parasitologists Baudena, Chapman, and Horohov note that in foals previously unaffected by cyathostomes, the initial infection results in the majority of the larvae maturing to adults, whereas in adult horses which have been frequently exposed to cyathostomes, most of those worms are encysted. (32)
EL3s can stay in the horse or donkey for years, (33) or as little as 8 weeks. They eventually develop into L4 (4th stage larvae) - when this happens, they emerge from the cyst and enter the large colon (and then become L5 and adults, and the cycle starts again). If there’s a huge amount of them, the emerging may kill a horse, if there are less but a lot, the horse could get colic and/or scour and /or get edema.
When they emerge they release toxins from accumulated larval waste products, and THIS is the problem with these worms. (34) Horses or donkeys can die when a huge amount of L4 burst through the colon wall and they become sick when a small number burst through. (35) This is known as “Larval Cyathostomosis.”
To recap, when a horse or donkey which has a lot of encysted cyathostomes is wormed with a standard wormer, the standard wormer kills the small strongyles living in the lumen – it kills the ones of course that are not encysted. So they die and are passed out of the horse. If there were a lot of small strongyles in the lumen of the horse - guess what happens next! Because a lot of small strongyles have been killed in one go, those nasty encysted small strongyles who have been sitting safety inside the horse untouched by this standard wormer are given the signal to emerge en masse to replace the ones that the standard wormer killed. (36)
(If instead you worm with moxidectin (for example Equest/Quest) or a multiple-days dose of fenbendazole (for example Panacur), not only are the non-encysted adult small strongyles killed, but you will also take out a whole bunch of the encysted ones who were waiting to replace them.)
So, the standard wormer kills all the small strongyles in the lumen. The dead ones pass out of the horse in the droppings. Because they are suddenly not there anymore, the encysted small strongyles (which have been untouched and unharmed by the standard wormer) are given the signal to replace them. So a huge amount of them burst out all at once, right through the wall of the horse’s large intestine.
Larval Cyathostomosis
The symptoms of Larval Cyathostomosis are weight loss, diarrhea and/or subcutaneous edema. (37) The horse may have a sudden onset of diarrhea caused by the emergence of the encysted larvae through the lining of the cecum and ventral colon. It can be life-threatening. Parasitologist Jane E. Hodgkinson states, “Furthermore, the disease is difficult to both diagnose and treat, with a high fatality rate despite intensive treatment.” (38)
“The prognosis in suspected cases must be guarded because the underlying pathology can be severe without the animal showing marked clinical signs, and only less than 50% of the diarrhea cases respond to symptomatic treatment.” (39)
“The disease is difficult to both diagnose and treat, with a high fatality rate despite intensive treatment.” (40)
The contributing factors include seasonal conditions (autumn and winter), young horses (often 6 years of age or younger, although older horses have died from Larval Cyathostomosis), and horses recently dewormed by a wormer which cannot affect the encysted stages but which does kill the lumen-dwelling larvae and adults. (41) Parasitologist C. Monahan states, “The onset of classical larval cyathostomosis has been associated with recent anthelmintic treatments effective for removal of the lumen-dwelling stages.” (42)
“The onset of classical larval cyathostomosis has been associated with recent anthelmintic treatments effective for removal of the lumen-dwelling stages.” (43)
You can see the problem when there are encysted worms sitting there for possibly 3 years, worms that your standard wormer won’t touch, so someone could be worming the horse religiously with standard wormers and the encysted worms won’t be affected in the slightest.
Research has shown that cyathostomes have become more and more important as a cause of sickness and death in horses, and today are considered the main reason for worming horses. (44)
A standard wormer – other than a single dose of Equest/Quest or ComboCare or a 5 day dose of Fenbendazole/Panacur - does NOTHING against encysted small strongyles, it has NO EFFECT whatsoever.
If you have never given moxidectin (- or fenbendazole for 5 consecutive days at the recommended dose for encysted small strongyles -) well.... that could be a cause for concern, depending on your geographical location, and your horse’s circumstances. Of course, some horses are more prone to worm infestation than others – the old saying “Some of the horses have most of the worms” is correct. Many healthy horses have an effective immune response to worms which keeps the numbers low, unless the horse becomes sick, badly fed or gets a large number of worms. Parasitologists consider that in any group of horses, 20% will carry 80% of the worm burden. (45) This, by the way, may lead to natural alleged dewormers wrongfully getting the credit for being successful. (46)
At any rate, egg counts do not show how badly a horse is infested with encysted small strongyles. This means the egg count could be zero but the horse could be infested with these worms.
I’ll repeat this! Egg counts do NOT show how badly a horse is infested with encysted small strongyles. This means the egg count could be ZERO but the horse could be INFESTED with these worms.
What even many veterinary surgeons do not say on their websites is that the only active ingredient that kills encysted small strongyles in a single dose is moxidectin, available in, for example, Equest/Quest (name depending on which country you live in) or ComboCare. Fenbendazole at the dose rate of 10 mg/kg over a 5 day course is also effective.
I recently saw a popular wormer brochure that stated, “100% effective” and the same claim was made on the company’s website. This is a false claim, as those wormers were not fenbendazole or moxidectin, so could not be 100% effective. In fact, no wormer can claim to be 100% effective, but the chemicals in the advertised wormers had no registered claim to affect encysted small strongyles. How did the company get away with these false claims? I have no idea, but the point is, they did! In fact at the time of writing, these claims are still on their advertising material and on their websites.
As just mentioned, fenbendazole, the active ingredient in, for example, Panacur, can kill some of the encysted stages including L3 if given 5 days in a row at 10 mg per kg. (47) Resistance to a single dose of fenbendazole for encysted cyathostomes has been demonstrated, (48) you do need to give it for 5 consecutive days.
Fenbendazole (Panacur) effectively treats and controls large strongyles (adults and migrating larval stages of Strongylus vulgaris; adults and tissue larval stages of Strongylus edentatus), small strongyles (cyathostomes) including encysted early third stage (hypobiotic), late third stage and fourth stage mucosal cyathostome larvae, pinworms (Oxyuris equi), ascarids (Parascaris equorum), and arteritis (inflammation of the walls of the arteries) caused by fourth stage larvae of Strongylus vulgaris in horses. (49)
Parasitologists Swiderski and French state that dosing with fenbendazole may be inferior to moxidectin in the prevention of the introduction of resistant worms in new arrivals and suggest that new arrivals should be treated with fenbendazole regimens followed by a single dose administration of a macrocyclic lactone to remove the remaining worms. (50) This is the regime I personally use.
A horse can be fat and shiny and have a heavy worm infestation. Fat shiny horses have died from worms. Don’t be fooled into thinking a horse is not heavily infested with worms just by appearance.
If you have read my book Natural Horse Care The Right Way, you will know that I have often spoken with Maria Daraio of Dara Park Stud in Australia about the tragedy of thinking that natural wormers and certain chemical wormers are efficient. Both Maria and I have seen horses die horrible deaths from encysted cyathostomes. Maria’s story is in that book, but it is so important that I have repeated it here. Maria breeds Arabians as well as Quarter Horses. I asked Maria to write about her experiences with Larval Cyathostomosis, and this is what she said:
Our problem with cyathostomes began in 2001 when a rising yearling Quarter Horse filly suddenly started to scour seriously. She went from a nice, round filly in excellent condition, to a rake in a matter of days and we called the vet in to deal with it. We had no idea what was wrong with her and we fought for weeks to pull her through.
She was put onto drips, antibiotics by the bucketloads and I remember using our big tree to hitch up the drip in the dark. She suffered greatly and was humanely euthanized not long after she developed a neck abscess due to having so many injections. The vets were absolutely in the dark as to what had caused it.
For the next five years we embarked on a horrible rollercoaster ride whereby we periodically would see an otherwise healthy youngster come down with serious scours, get treated by one vet or other and then ultimately die. Not all died and we did experience varying degrees of success in saving these sick horses. Each time the nightmare would repeat itself and we began to notice a correlation between the onset of the scouring and the onset of wet, cold weather. We mentioned this to our then vet and he just shrugged his shoulders and continued to prescribe one antibiotic or other.
We also then went through a stage where new born foals were coming down with deadly scours at anything from a week to twenty-eight days after birth. Again they were plied with all the top shelf antibiotics available under veterinary supervision.
Some foals survived whilst others did not. We soon discovered that the white anti-scour powder that the vets were invariably supplying was absolutely useless, and that any foal injected with just procaine penicillin was also doomed to die.
The vets at this stage decided that these foals were suffering from salmonella even though the bug itself was only ever found in ONE horse. (Not surprising since our research suggested that all horses carry the bug. It is under duress that it proliferates and then causes problems). The vets stopped looking for a cause after this as they believed they’d found the cause in Salmonella.
I was even chastised when I decided to treat one of our sick youngsters myself as I was pregnant at the time. The vet felt it was too dangerous for me and my unborn child since the filly was carrying a deadly bacteria. Unfortunately, unless I wanted her to die, I had no choice but to medicate her.
Time wore on and every season we’d lose both foals and older youngsters to the mysterious ‘bug’. Those that survived ended up looking shocking and never thrived. It was a chance visit to another stud that saw the introduction of ‘Protexin’ to the recovery regime. From then on, at least the survivors would actually recover with no apparent side effects. Then the season we bred our A class supreme champion filly, Dara Park Sarina, we had a good 75% of our foal crop come down with the ‘scouring bug’ and we nearly lost Sarina. She was born an absolutely stunning filly and we knew she was special. But within the eight days of life she came down with the scouring. We were desperate to save her. The vet we were using by this stage was in my opinion arrogant enough to think he was better than any of the other vets and that he knew what the problem was. He insisted it was clostridia and the fact that our property had been a cattle farm before we bought it sealed it for him. He supplied us with a new antibiotic and advised us to use Scourban. The filly kept deteriorating and it was obvious we were going to lose her. I called another vet and she prescribed throwing out the antibiotic and putting her onto Protexin instead. I’d seen too many foals die of this problem and I was not interested in allowing this filly to die so I refused to do so. What I did do was to combine the two treatments as well as adding Gastroshield to the mix. Unbelievably, the next morning, instead of waking to a dead filly foal, I found her very much on the road to recovery!
Whilst we’d stumbled onto the correct treatment of the symptoms, we were still none-the-wiser as to what was actually causing the problem. By this stage the ‘bug’ had moved onto our gorgeous black Arabian pony mare, Gembrook Halloween. We fought for several months to save her with all sorts of things tried. Unfortunately she was in foal and this limited what could be administered. She foaled early and seemed to recover suddenly. But then at two days post foaling disaster struck and the mare collapsed. The foal was under her and when she went to get back up again she stepped on the filly’s leg and snapped it in half. To cut a long story short, we saved that filly but lost the mare two months later. It had been a four month battle which we unfortunately lost due to vets being caught unaware. Halley had stopped scouring but had become severely anemic and lactating was just too much for her. Whilst they worked hard to save the filly with regular changes of casts and x-rays to her leg, it had never crossed their minds to check the mare’s blood levels.
Then a breakthrough occurred! A two year old Quarter Horse colt became sick and then started to scour badly. By this stage our vet clinic had two new young vets who were not so convinced they knew the answers. They fought long and hard to save Player but unfortunately we lost him one cold night. The vets came out and by the lights of their car they did an autopsy, taking every organ that they could. They were adamant they were going to find out the answer to what was causing the problem and find out they did. I can still remember the wording of the autopsy report. There was no evidence of anything wrong with the colt! All they could find was ‘an unusually large load of cyathostomes’. So there it was..... WORMS!
We had always employed a strong worming program and whenever the vets came to see yet another sick horse, they would always ask, ‘Has this horse been wormed?’ Our answer was always ‘Yes!’ They never once asked had we wormed the horse with Equest. That one question would have saved so many horses and it really makes us angry to consider this. We felt betrayed as we’d always looked after our horses very well and had always drenched regularly. Player had gone from a healthy 2 y.o. to very sick very quickly. We originally did a fecal worm count as soon as he became sick. It showed a ZERO worm count!!!! We were informed after the autopsy results came through that encysted cyathostome eggs do not show up in a fecal worm count as encysted cyathostomes do not lay eggs. The entire herd of horses at Dara Park was ordered to be drenched with Equest THREE times over SIX WEEKS.
It took another couple of years to learn about looking after our dung beetles and about harrowing in the middle of summer to kill the worm larvae. Once this was all in place, we had no further problems with scouring horses. These days we make sure the horses get a dose of Equest in January as it is the ONLY wormer that kills the cyathostomes in a single dose when they are actually encysted within the horse’s gut. Then they get done again once the weather changes from Summer to the first Autumn rains. Throughout the wet times of the year we dose them with Equest. Every broodmare is drenched the day she foals with Equest and then the foals are drenched with another dung beetle friendly drench as of one month of age. Then they get their first Equest dose at three months of age.
Since adopting the above regime, we have not had to open the Scourban bottle and although we always have the appropriate antibiotics, probiotics and Gastroshield in the fridge, we have not had occasion to use it. It has been a long journey and I shake my head in disbelief when I read the comments from some ill-informed horse owners who think that following the ‘natural’ worming approaches are going to protect their horses. Every time I read about some poor horse suddenly becoming sick and passing away in agony, I grit my teeth as I know how hopelessly ill-equipped to handle this problem most vets actually are. Too many of them are completely ignorant of the vital importance of including Equest in one’s worming regime for one’s horses. Too many are ignorant of how to actually save a horse that comes down with a proliferation of the worm. Too many owners are also in the dark when it comes to encysted cyathostomes.
When a horse is not treated as outlined above, the cyathostomes burrow into the horse’s gut. Once here they are completely immune to any of the other otherwise efficient wormers. This happens over the Summer months here. Once the weather starts to change and it gets wet, these worms migrate from the gut wall and leave sometimes a heavily damaged gut behind. This damaged gut becomes infected and inflamed which is why the horse now needs antibiotics. Unfortunately, if the inflammation is too severe, the horse now also needs steroid treatment to help arrest the severe scouring as well as the Scourban. The treatment now appears simple enough but this is certainly one case where prevention is far better than cure. A great deal of suffering on the part of the horse can be avoided if it is placed on a worming program that includes Equest.
The above heartbreaking story about her experience with Larval Cyathostomosis was written by Maria Daraio of Dara Park Stud in Australia. Her website is darapark.net.
In many cases, horses may show no signs of encysted small strongyles at all and appear perfectly healthy for some time. Encysted small strongyles can sit in the lining of the colon for 2 to 3 years or more and there is no way to detect their presence, no way at all. Many sudden mysterious deaths usually attributed by default to snakebite actually may well be due to Larval Cyathostomosis. I have known of horses who were fine and fat and shiny in the morning to be dead suddenly that night from Larval Cyathostomosis. In fact, I knew of two in 2008 who were from a hot dry climate out in western NSW, Australia.
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Tapeworms have been associated with colic, (51) specifically spasmodic colic (22%), impaction colic (81%) and 100% of intussusception colic. (52) The colic often recurs and the site where the tapeworms were attached often becomes infected or abscessed. (53)
There are three species of equine tapeworms: Anoplocephala perfoliata, Anoplocephaloides mamillana, and Anoplocephala magna.
The occurrence of tapeworms varies by location, but far more horses in temperate climates are affected. (54) There does not appear to be an acquired or age resistance to this parasite in horses because all ages, including older ones, can be infected. (55)
A horse needs to eat mites containing the cysticercoids stage of the parasite to become infected with a tapeworm. These mites are normal soil mites which live in pasture, in hay, and even in processed feedstuffs.
Tapeworm segments (56) contain both male and female organs. As they develop, their eggs disintegrate in the large intestine, and are passed in the manure. The mites eat the tapeworm eggs, which develop for 2 to 4 months inside the mite before reaching the infective stage. (57)
Fecal Egg Counts are of little use in detecting tapeworm infestation. Murray noted, “In one report, fecal examinations were negative for tapeworm eggs unless there were at least 40 tapeworms in the horse.” (58)
For several years, pyrantel products have been used at a double dose to treat for tapeworms in horses. Murray notes that praziquantel is effective in killing tapeworms at dosages ranging from 1.0 mg/kg to 2.5 mg/kg (59) and the Merck Veterinary Manual states that praziquantel (at 1 mg/kg) appears to be effective in removing Anoplocephaloides mamillana but that pyrantel products are not. (60) However, Murray states that normal dosages (6.6 mg/kg) of pyrantel pamoate are 87% effective, while double the normal dosage is greater than 93% effective. (61) Murray also notes that pyrantel tartrate (2.65 mg/kg) removes Anoplocephala species. (62) Reinemeyer et.al. noted that in two dose-confirmation studies, a single oral treatment of pyrantel pamoate at a dose rate of 13.2 mg/kg was greater than 95.5% effective against Anoplocephala perfoliata in naturally-infected horses. (63)
Murray notes that the traditional recommendation to treat in the spring and the fall, has not been critically examined and that exposure to mites may occur at other times of the year. (64)
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Chapter 9. Lungworms (Dictyocaulus arnfieldi)
Donkeys are generally named as the culprit in carrying these worms and infecting horses. However, lungworms have been found in horses with no previous donkey contact (65) and transmission from horse to horse has been discovered. (66) With horses, it used to be considered that lungworms are usually only of concern in foals, but infections have been found in horses up to 20 years of age, and it is now considered that horses do not have age immunity to lungworms. (67) However, foals are far more susceptible than adult horses. (68)
Mature lungworms live in the bronchioles and grow up to just over 3 inches (8 cm) long. They lay eggs in the air ways. The donkeys or horses cough up the eggs, then swallow them, and the eggs hatch along their way to being passed out in the manure. (69) The infective stage only takes five days on pasture. After they are swallowed, the infective larvae migrate from the intestine via the lymphatics and the pulmonary arterial system to the bronchioles and bronchi where they mature. Lungworm larvae do not generally develop into adults in the mature horse.
Horses and donkeys infected with lungworms can have a persistent dry cough. It has been reported that the response to lungworm in horse varies greatly with the individual. (70) Research has found however that there is no seasonal variation in lungworm and that adult lungworms have been found in the lungs of horses and donkeys throughout the year. (71)
Generally, donkeys will not present with any clinical signs despite having large lungworm burdens. (72) However, secondary problems related to lungworm infestation include influenza. (73)
These are difficult to detect in the live horse, and the usual diagnosis is the discovery of eosinophills in tracheal mucus. (74)
However, they can be detected in the live donkey by the modified Baermann technique of Fecal Egg Count, if appropriate care is taken with the samples. (75)
Thiabendazole at the dose rate of 440 mg/kg has also been used successfully to treat donkeys and horses. (76) However, some horses and donkeys showed depression and anorexia after treatment. (77)
Another study used oxibendazole at the dose rate of 5 to 15 mg/kg, and found it to be ineffective against lungworm. (78) Likewise, a single dose of fenbendazole at the dose rate of 7.5 mg/kg to 30 mg/kg) and repeated treatments (2 x 15 mg/kg) also failed to eliminate lungworm infections in donkeys. (79) In one trial in donkeys, mebendazole was ineffective when given orally at a dose rate of 4.3 to 5.7 mg/kg for five days but when given at the higher dose rates of 15.2 to 20 mg/kg was 75 to 100% effective. (80)
An older study recommended that in a situation of donkey-only grazing, donkeys can be treated for lungworm in the spring, and new arrivals should be isolated and treated. (81) A more recent study found that donkeys treated with moxidectin tested negative for lungworm larvae 21 days after treatment. (82) Other studies have shown that ivermectin in combination with change to non contaminated pasture was effective. (83) Albendazole (Valbazen) at the dose rate of 25 mg/kg twice daily for five days has been demonstrated to eliminate lungworm infections in horses. (84) Thiemann and Bell state that treatment of choice in donkeys is ivermectin at 200 mg/kg. (85) They also state that reinfestation is slow, especially if ivermectin or moxidectin is being used. (86) The Merck Veterinary Manual also recommends ivermectin or moxidectin for lungworm treatment. (87) Purdy suggests treatment for lungworms in horses and donkeys is ivermectin with a repeat treatment in three weeks. (88)
Lungworm larvae can live for a long time in a cool, moist environment, but will not survive a heavy frost.
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Chapter 10. Pinworms (Oxyuris equi)
These worms are not particularly important. They are the cause of the horse rubbing its tail. This only happens when the worms emerge to lay their eggs. If your horse rubs its tail, wash the area with warm water to clean off the worms and then dispose of the cloth or towel immediately. The eggs will fall off the horse and cling to fences, feed bins, buckets, or anything else in the environment, and infect other horses.
Pinworms do not do much damage to the horse, and ivermectins kill them easily. The adults live mainly in the small colon. The female is 3 to 6 inches (7.5 to 15 cm) long and the males are much smaller, and there are fewer males about. The eggs show up in a routine Fecal Egg Count.
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Chapter 11. Stomach worm (Trichostrongylus axei)
The mature stomach worm lives, as you would expect, in the stomach. This worm if present in large numbers has been known to cause mild intestinal disturbances and chronic catarrhal gastritis. The adults penetrate the mucosa and produce nodular areas resulting in thickened mucosa causing erosions and ulcerations. (89)
The horse eats the third stage infective larvae from hatched eggs on the ground, the manure comes out with eggs in it, and the horse eats these eggs, quite direct. Other fun facts about this worm are that it is small, less than 1/third inch long (8 mm) and also infects ruminants.
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Warbles are the larvae of the bovine (cattle) warble flies (Hypoderma bovis and Hypoderma lineatum). These are quite uncommon in horses. They are a cattle worm, but as ivermectin kills them easily it’s pretty rare to find them in either horses or cattle these days. At any rate, they are usually found only in horses which are kept near cattle.
The adult flies attach their eggs to the hair on the lower legs. The eggs hatch and the larvae penetrate the skin, migrate, and end up at the neck, back or withers where they form nodules. The larvae usually die in the horse, but in cattle they mature and emerge through the skin.
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Chapter 13. Threadworm (Strongyloides westeri)
Threadworm usually affects foals under 6 months of age (90) where it lives in the small intestine. However, mares sometimes harbor larval stages which are activated by foaling which causes them to move to the udder where the worm is transmitted via the milk to the foal. (91) Ivermectin has a registered claim to kill them (92) as does oxibendazole. (93) Moxidectin plus Praziquantel will too but you cannot (must not) give that to a newborn foal.
These worms are not generally serious but can cause scouring in foals at around ten to fourteen days of age. Treatment is simple - make sure the mare is not infested with these worms, as obviously, a mare who is not infested cannot pass the worms onto the foal. If in doubt, give the mare a dewormer on day of foaling. This is of course a far better option than worming a newborn foal.
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Chapter 14. Liver fluke (Fasciola hepatica)
The horse is not a natural host for the liver fluke, and again, Fecal Egg Counts are of no use detecting this worm. Signs of infestation in the horse are irregular heartbeat, weight loss, and chronically soft manure.
Damage to the liver is caused by the migration of the immature fluke. Adult fluke live (and lay eggs) in the bile ducts where they drink blood and cause tissue irritation. These eggs hatch into an immature fluke (“miracidium”), which then infiltrates a snail in a wet or damp area. The fluke egg needs to fall into water for the miracidium to develop. In the summer, this takes two to four weeks at summer temperatures. The infectious stage becomes encysted on grass, and the fluke is eaten by the horse or donkey.
One study found that a patent infection was established in only one out of ten horses given oral doses of up to 800 metacercariae (94) (encased encysted stage) and concluded, “The experimental data show that the horse exhibits a pronounced resistance to the establishment of a liver fluke infection.” (95) These findings were in agreement with an earlier South African study. (96) However, a Bolivian study in a high endemic region for Fasciola hepatica found that donkeys are a main host in that region. (97)
One study asserted that a safe method of treatment for infected horses is an oral dose of oxyclozanide at a dose rate of 15 ml/50 kg body weight. (98)
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Chapter 15. Chemical dewormers
Safety of chemical wormers
Sadly, there is a lot of unfounded nonsense around about the supposed dangers of chemical wormers. Here are the facts. Herbal wormers do NOT work against the deadlier varieties of horse worms, and these worms do KILL horses. We do need to use chemical wormers, very sad but also very true.
Now, these days, chemical wormers made for horses are very safe. (99) Some wormers are safer than others. You will see unsupported false scaremongering on the net that Equest/Quest (moxidectin) is unsafe in a small overdose. In the USA, Quest is registered for foals over the age of 6 months. It used to be 4 months of age, but misuse of the product in dogs caused the age downgrade. (100) In Australia, Equest (same product, different name) is recommended for foals over the age of 2 months.
At any rate, you must be careful not to overdose Quest/Equest in foals. You can ask your veterinary surgeon to come and estimate your foal’s weight, or you can go to this website (gaitedhorses.net/Articles/horseweight.html) where you can enter the girth and length, and the site calculates the estimated weight. Be VERY careful with weight tapes as they can be inaccurate.
A Drug Tolerance Test on Quest (101) (also known as “Equest,” and the active ingredient being moxidectin) –administered five times, and six times the recommended dose rate of Quest Plus Gel to young foals and horses. Fourteen hours after treatment, one foal given five times the recommended dose rate showed ataxia, incoordination, lethargy, depression, and droopy lips and eyelids. This foal was stated to be “normal” by the 24 hour observation point. Another foal also showed ataxia, incoordination, lethargy, depression and droopy lips and eyelids at 24 hours post treatment, and this foal returned to normal by the 48 hour observation point.
It also noted that two of the four foals that received a dose at five times the recommended dose rate did not show any signs of adverse reaction.
The study stated, “All animals returned to normal by 48 hours post treatment.”
One of the two yearlings administered Quest Plus Gel at five times the recommended dose showed ataxia, incoordination, lethargy, depression, and droopy lips and eyelids at 23 hours post treatment and returned to normal by the 48 hour observation point. Both yearlings that were administered Quest Plus Gel at six times the recommended dose also showed ataxia, incoordination, lethargy, depression and droopy lips and eyelids at 14 hours post treatment. Both yearlings had returned to normal by the 24 hour observation point. (102)
The trial Target Animal Toxicity Study – Study No. 0696-E-US-08- 01 did extensive tests on four month old foals, some on 4 times the recommended dose level of Quest weekly for three weeks. Hematology, Coagulation, Serum Chemistry, and Urinalysis were carried out on the foals and the results stated, “A comparison of pre and post treatment hematology, coagulation, clinical chemistry, and urinalysis values indicated no biologically significant changes.”
Pathology observations were as follows, “No gross lesions suggestive of treatment-related toxicity were observed at necropsy. Similarly, microscopic evaluation of all major tissues obtained from test animals in the high-dose (4X) group at necropsy revealed no histopathologic changes indicative of a toxic effect.”
The conclusion of Target Animal Toxicity Study – Study No. 0696-E-US-08- 01 was as follows, “Under the conditions of this study, 12 of the foals treated with the final Quest Plus Gel formulation showed transient signs including slight depression, slight ataxia, and/or droopy lips. All affected test foals returned to normal without intervention or significant long-term health effects. No other clinical or pathological effects were noted in any of the treated foals.”
Don’t overdo chemical wormers!
Equest/Quest (moxidectin) does not need to be given as regularly as other wormers (as it has been demonstrated to have an 84 day Egg Reappearance Period (103) as opposed to 56 days for ivermectin (104), so use it according to instructions. This reduces the amount of chemical wormer going into your horse.
Q: What happens to the encysted cyathostomes killed by moxidectin or fenbendazole?
A: They simply dissolve and are reabsorbed.
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Chapter 16. Herbal and “natural” – not for horses!
Black walnut. Has been shown to cause severe laminitis, and has been used by veterinary researchers specifically to bring on laminitis. (105)
Wormwood. The main variety is Artemisia absinthium and this is what absinthe is made from. Wormwood contains the toxic chemical monoterpene thujone and this is why many countries have banned the use and production of absinthe. It is a neurotoxin and has been shown to cause brain damage. (106) It traditionally was used to control roundworms in people, which is how it got its common name, “wormwood.” Long term use in people has been shown to cause hallucinations, tremors, convulsions, and even paralysis. (107)
However, a recent study concluded, “The results of the present study suggest that A. absinthium extracts are a promising alternative to the commercially available anthelmintics for the treatment of GI nematodes of sheep.” (108)
Purgatives: Cascara, senna, aloe
These are used as laxatives and the aim in using them for worm control is to cause bowel contractions in order to expel worms. Of course, this requires that worms are in the bowel in the first place, and it doesn’t take much common sense to see why it’s not a good idea to induce scouring in a horse!
Garlic as a wormer
There is zero evidence for this, and anyway, you should not feed garlic to your horse due to the reported toxicities (109) and risk of Heinz Body Anemia.
There is no scientific evidence that garlic is helpful for horses, rather, there is scientific evidence from several scientific studies that garlic is harmful to horses. (110) The feeding of garlic has been shown to cause Heinz body anemia. (111) It has been demonstrated that chronic supplementation with garlic at certain levels, beginning with less than 0.2 g/kg per day (100 grams = 3 ½ ounces in 1,100 lb = 500 kg horse) resulted in Heinz body anemia, as characterized by reduced red blood cell count, free hemoglobin, hematocrit, and haptoglobin; increased free bilirubin, mean red cell hemoglobin, mean red cell volume, platelets and incidence of Heinz bodies. (112)
One study found that the risk of feeding freeze dried garlic begins at 100 grams (3.5 ounces) per day. (113) Another study, by W. Pearson, has been cited on the net along with several inaccuracies.
Let’s get this out of the way first. W. Pearson states, “However, natural is not synonymous with safe, and horses will voluntarily consume enough garlic to cause Heinz body anemia which, if left unchecked, can be fatal.” (114) Pearson has now agreed that the horses in the study ate the large quantities of garlic due to the fact it was fed with molasses. (115) Now to the inaccuracies.
Inaccuracy 1
“She (Pearson) found that the garlic eaters showed changes in their blood chemistry beginning at around the third week, when garlic intake was four cups (560 grams) of freeze dried garlic per day.” (116)
Facts
Incorrect. Toxicity in the trial began at less than 0.2 g/kg per day, that’s 100 grams (3 ½ ounces) for a 500 kg (approx. 1,100 lb) horse, not 560 grams – 100 grams is a lot less than 560 grams!
A cup is a measure of volume, not weight. W. Pearson of course did not mention “cups” as it was a scientific study. However, if 1 cup of freeze dried garlic does weigh 140 grams, then almost three quarters of a cup of freeze dried garlic fed to horse per day is a toxic level!
W. Pearson wrote to me, “We need a lot more research before we can argue strongly either for or against its longterm use in horses.” (117) The reason for this is, that they do not know if the anemia which showed up in the third week of Pearson’s trial (as stated above) was caused by an increase in the dose of the garlic, or by the length of time the horses had been consuming the garlic. Her trial was a volumetric analysis (titrating) trial, starting with a total daily dose of 0.1 g/kg/day, working up to 0.5 g/kg/day over a six week period.
However, as I have said, the study found that garlic was toxic to horses in an amount as small as 100 grams (3 ½ ounces) a day. (118) Why would you want to feed your horse garlic? If your horse is about to be attacked by vampires, then it’s a good idea. Otherwise, bear in mind there is no evidence that garlic has any benefits at all for horses, and much evidence to show it is unsafe. Many people feed garlic, and as their horses do not die or become ill, and even look well, they assume garlic must be safe. If you want your horses to be the healthiest they can be, don’t assume that they are healthy just because they aren’t showing any obvious symptoms yet. There is a wide area between looking sickly and optimum health!
Garlic has been shown to be beneficial in some other animals. Don’t forget, what’s good for one animal is not always good for another. Lots of us eat chocolate, but it is commonly fatal to dogs. Garlic has been shown to lower cholesterol and triglyceride levels in humans, dogs and monkeys. (119) A study on the effect of garlic on blood pressure in human patients with and without elevated systolic blood pressure found that garlic did reduce systolic blood pressure in those patients who did have elevated systolic blood pressure. (120) Another study focused on a certain odorless form of garlic rich in bioavailable water-soluble organosulfur compound, which had a higher antioxidant activity than fresh garlic and none of its adverse effects. It concluded that the available evidence suggests that garlic in this form was of potential benefit in humans in reducing risk factors for cardiovascular and cerebrovascular diseases and dementia, including Alzheimer’s disease. (121)
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