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Feeding Garlic - The Great Garlic Debate
Dr. Karen Hayes, DVM, MS, discusses whether or not to feed your horse garlic as a feed supplement or fly repellent.
By Karen Hayes, DVM, MS
It's heartening to see how passionate readers are about the care of their horses--and their garlic!
The toxic element in allium (a family of plants including both garlic and onions) is well known to be a chemical called N-propyl disulfide. By altering an enzyme present within the red blood cell, it depletes the cell of a chemical known as phosphate dehydrogenase (PD), whose job is to protect the cell from natural oxidative damage.
When the PD level gets low enough, the hemoglobin in the cell oxidizes and forms a "bubble" called a Heinz body on the outside of the cell--it's quite distinctive and readily seen under the microscope. The spleen--which acts as a red-cell "bouncer" of sorts--quickly removes the deformed cell from the bloodstream. As more and more red cells are prematurely damaged and removed, as will happen from consistent poisoning with N-propyl disulfide, your horse gradually becomes anemic. This is called Heinz-body anemia.
The "toxic dose" of N-propyl disulfide, which is not well worked out in any species, is the amount thought to cause obvious poisoning, a sort of "9-1-1" situation. Cows are thought to be more sensitive to the toxin than are horses, but in one study published in 1972 in the "Journal of the American Veterinary Medical Association," the toxic dose in horses turned out to be considerably less than the 5 grams per kilogram of body weight reported in cows.
Here's what happened. When horses in a pasture dotted with wild onions came down with anemia (low red-blood-cell count), jaundice (increased bile pigments in the blood, causing yellowish discoloration of the gums and whites of the eyes), and reddish-colored urine, investigators decided to find out for sure whether onions had caused these symptoms.
To do so, they fed 1 pound of the onion tops per day to a healthy horse for 3 days, along with his regular feed, then 4 pounds on Day 4. From Day 4 through Day 8, his packed cell volume (or PCV, meaning his red-blood-cell percentage) dropped about 23 percent, from 30 to 23.
The investigators continued to give the horse onion tops on Days 9 and 10; by Day 11, his PCV had dropped to a life-threatening 13--he'd lost almost 60 percent of his red blood cells in 11 days!
Most of us with a rudimentary interest in equine toxicology have no quarrel with this report, but what would've happened to pasture horses if they'd eaten smaller doses of the toxin? Good question--and here's where the controversy comes in.
Some vets say the toxic effects are more gradual and insidious--but still very real--when a lower dose is consumed on a regular basis, resulting in a mild anemia without obvious symptoms. This has been my experience in a practice. I see a handful of cases of Heinz-body anemia every year in horses that grazed on wild onions growing amidst the grass in their pastures, or helped themselves to discarded onions and leeks in the compost pile, or raided the garlic patch in the garden.
No well-designed, formal research has been conducted on the ill effects of lower doses of garlic on horses. But, to be fair, there also hasn't been any well-designed, formal research on the benefits of garlic in horses. For example, I've seen lots of horses reeking of garlic and crawling with flies, though garlic is reputed to be an effective fly repellent.
I've no doubt those of you who are feeding garlic to your horses are doing so because you want only the best for them--the best health and the highest degree of comfort. That's why I feel it's important for you to understand it isn't enough to say garlic is safe just because you haven't seen any ill effects in your garlic-supplemented horse. Depending on the dose, and the frequency and duration of dosing, there could be low-grade deleterious effects, due to red-blood-cell damage that's not enough to cause a 9-1-1 situation, but just enough to cause a mild anemia that might not be outwardly evident. It might affect your horse's stamina, energy level, or resistance to disease.
Until these suspicions are investigated and repudiated, how much risk are you willing to take? Until well-designed, formal research is done on garlic's risks and benefits, specifically in horses, it seems the only safe avenue is the avenue of caution. At the very least, I wanted each of you to make your decisions with benefit of all available information, including longstanding reports from researchers far greater than me, indicating that the popular garlic bulb has a dark side.
I think I'll cut out garlic in Sonny's diet hehe...I was wrong ....sorry :(
Well I guess it did say there is no negative effects, but I'll just leave it out all together
Here's another one:
In response to your question on garlic I will provide some background and some studies that have shown its effects. Garlic is a plant in the genus Allium. It is given to horses because it is believed to act as an insect repellent, anti-inflammatory, anti-histamine, anti-bacterial, disinfectant and anti-allergic. Garlic is related to onions, shallots, and leeks. Years ago, horses were discovered to become ill after consuming large quantities of wild onion. A study was performed in 1972 to test the effects of onion intake in horses. The horse in the study was fed onion tops in large daily quantities. The horse became anemic and lost most of its red blood cells within 11 days.
The anemia is caused by a specific chemical element of allium plants, N-propyl disulfide. The chemical is responsible for altering an enzyme in the red blood cells of the horses. The changes cause the red blood cells to deform and be removed by the spleen. This type of anemia is called Heinz-body anemia.
The issue with garlic is that it has undergone little testing of its own in regards to horses. Cats, dogs, and other animals are known to have this reaction to garlic as well as onions. Some claim horses have been known to show signs of anemia after an overdose of garlic. The worry is that the same effects could occur with small doses over an extended period of time. Studies about the effects of garlic on horses are only a recent occurrence.
In 2005 a study was published that tested the effects of garlic on horses. A study performed at the University of Guelph in Canada tested 4 horses; two given garlic in their daily diets and the other two with a garlic-free diet. The amount of garlic given was increased daily, reaching a maximum of 5 cups per day. The study lasted for 71 days. The blood chemistry of the garlic-fed horses showed signs of changing within three weeks. The horses did show signs of Heinz-body anemia in reaction to garlic exposure. However, the study gave doses of garlic many times the size of those given to horses in real practice. They estimated that effects would appear if horses were fed 500 grams daily.
If you are feeding 10 ml daily, it would not be a high enough dose to cause harmful effects. However, little is known about the long-term effects of such exposure. Some believe that in the long term, although signs would not readily show, the exposure could cause loss in stamina, energy, and resistance to disease. Plus, these studies are all concerning pure garlic. The garlic found in different horse products is considered less controversial. This is because many of the products that contain garlic lack the active ingredient (allicin) that is the cause for concern. This may cause the products to be less effective than straight garlic, but they are thought to be safe. The studies done to date still have no measure for the correct daily dose of garlic that should be given to horses. Some studies believe that the low-dose, long-term exposure would have the same negative effects as the high-dose exposure in the experiments. Others believe that the low dosage could not build up the same effects.