I was recently talking to an experienced horsewoman who is fairly high up in a large TB operation- farms in various provinces, breeding and foaling as well as training. She told me that 80% of their horses have been diagnosed with thyroid deficiency and are on thyroid replacement. I expressed surprise, and she assured me vet did bloods work to check every time. Is this really a thing- I don`t recall any of the OTTBs I know being on thyroid replacement.
The problem is levothyroxine is performance enhancing. Not in a “give a horse a dose and he goes from claimer to stakes winner” sense, but it increases metabolism so horses put on weight and muscle… and occasionally die of cardiac arrest.
Of course they “all test low” and need the script… just like they all needed Winstrol back in the day. Plus, a lot of the other junk we give them DOES cause temporary human-induced hypothyroidism, so it’s not difficult to produce low blood work. And it’s something that’s hard to test for because the metabolites of the drug are the same as the natural hormones the body produces.
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MMM- that’s more or less what I thought, altho I have never heard of supplementing with L thyroxine to INCREASE muscle bulk. I would expect it to cause weight loss and weakness, as well as osteoporosis (and of course over excitability!) though that is dose related. At least that’s what it does in humans! The heart problems associated with hyperthyroidism cause rapid heart rate and arrythmias which could lead to cardiac arrest.
What are the substances given to cause thyroid levels to test low in these presumably healthy young horses?
It doesn’t “bulk” their muscles, it boots their appetite so they clean up better without just putting on fat. Keeping race horses eating in training is a very big thing.
Horses don’t show adverse effects of hyperthyroidism in the same manner as humans, but it does increase heart rate. Some veterinarians don’t even believe horses experience thyroid problems period… just like other vets don’t believe supplementing with levothyroxine is consequential. But it has been documented that NSAIDs, ulcer medications, steroids, sedatives, and some antibiotics can decrease thyroid hormone levels… find me a race horse who isn’t treated with at least one of those at some point.
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Thanks, interesting…
Another thing to ask about when considering an OTTB.
My vet doesn’t believe it does anything for racehorses. In the “real” vet world, it is prescribed for overweight horses and ponies to help with weight control, so it does not make sense that it boosts appetite. Yes, it stimulates the metabolism, hence the use for weight control. It’s not really performance enhancing, if anything, it makes it harder for them to keep weight on. The bit of research I’ve done on it make me wonder why any race horse trainer would use it. To me, it may even have the potential to increase bleeding.
http://equimed.com/drugs-and-medications/reference/levothyroxine-sodium-powder
[h=2]Side Effects[/h]
When administered at an appropriate dose, no adverse effects have been reported. [h=2]Precautions[/h]
Bioavailability differences have been reported in different products. It is recommended that a reputable brand be selected, and that brands should not be indiscriminately chosen or changed.
Compliance with therapy as prescribed is very important and the horse should be monitored closely for symptoms of hyperthyroidism, including tachycardia, polyphagia, excitability, nervousness, and excessive panting.
Levothyroxine should not be used in horses with myocardial infarction, thyrotoxicosis, or untreated adrenal insufficiency. It should be used with caution in horses that have cardiac disease, diabetes, or are advanced in age.
Levothyroxine sodium is FDA-approved for use in horses. It is a prescription drug restricted to use by or on the lawful written or oral order of a licensed veterinarian.
In cases of competition horses, check with the proper individual regulatory body regarding use. [h=2]Interactions[/h]
Levothyroxine increases the actions of epinephrine, norepinephrine, and other catecholamines and sympathomimetics. It may increase the anti-coagulation effects in horses on warfarin. In horses with diabetes, thyroid hormones may alter insulin requirements. Levothyroxine may decrease therapeutic effects of digoxin or digitoxin. [h=2]Overdose[/h]
Chronic and/or acute overdosage will produce symptoms of hyperthyroidism, excitability, nervousness, and excessive panting. If this occurs, a veterinarian should be called. Treatment is supportive and symptomatic. Oxygen, artificial ventilation, cardiac glycosides, beta blockers, fluids, and antipyrexic agents may be necessary in extreme cases.
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[h=2]Side Effects[/h]
When administered at an appropriate dose, no adverse effects have been reported. [h=2]Precautions[/h]
Bioavailability differences have been reported in different products. It is recommended that a reputable brand be selected, and that brands should not be indiscriminately chosen or changed.
Compliance with therapy as prescribed is very important and the horse should be monitored closely for symptoms of hyperthyroidism, including tachycardia, polyphagia, excitability, nervousness, and excessive panting.
Levothyroxine should not be used in horses with myocardial infarction, thyrotoxicosis, or untreated adrenal insufficiency. It should be used with caution in horses that have cardiac disease, diabetes, or are advanced in age.
Levothyroxine sodium is FDA-approved for use in horses. It is a prescription drug restricted to use by or on the lawful written or oral order of a licensed veterinarian.
In cases of competition horses, check with the proper individual regulatory body regarding use. [h=2]Interactions[/h]
Levothyroxine increases the actions of epinephrine, norepinephrine, and other catecholamines and sympathomimetics. It may increase the anti-coagulation effects in horses on warfarin. In horses with diabetes, thyroid hormones may alter insulin requirements. Levothyroxine may decrease therapeutic effects of digoxin or digitoxin. [h=2]Overdose[/h]
Chronic and/or acute overdosage will produce symptoms of hyperthyroidism, excitability, nervousness, and excessive panting. If this occurs, a veterinarian should be called. Treatment is supportive and symptomatic. Oxygen, artificial ventilation, cardiac glycosides, beta blockers, fluids, and antipyrexic agents may be necessary in extreme cases.
http://equimed.com/drugs-and-medications/reference/levothyroxine-sodium-powder
It actually makes it harder for horses to keep weight on, and is mainly used (in the real world, not the race track world) to help overweight horses and ponies. I would not, in a million years, use it on a race horse. I even wonder if it could make them more prone to bleeding.
@Palm Beach I have worked in more than one barn who fed it to every horse. It keeps them eating. I’m saying this from first hand experience.
In your overweight horses, the increased metabolism + feed restriction helps them burn off those cresty fat pockets. But with race horses, they gain a better appetite. They have more energy. They train better. Therefore, they get more fit. And then occasionally, their hearts give out.
I’ve also known a couple breeding farms who feed it to their stallions to keep their libido up during breeding season. Whenever I hear a stallion died of sudden cardiac arrest, I always wonder… but then again, my best horse died of sudden cardiac arrest that certainly was not a result of any pharmaceuticals, so my speculation is unwarranted.
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It’s honestly just a money maker for the vets. The science does not agree with what you are saying. All the science says that Levothyroxine is an appetite suppresant and there is absolutely no medical evidence to support the use of it in horses to increase appetite. It’s all the opposite. Your anecdotal experiences are not science, probably more the result of good management. Baffert used it, so of course now everyone uses it.
If they stop eating or don’t eat good there is a problem that needs to be addressed, usually ulcers.
Polyphagia is a symptom of hyperthyroidism - TOO MUCH. If the horse exibits those symptoms, he’s been overdosed. The correct dose does NOT cause polyphagia.
The correct dose doesn’t cause polyphagia when the horse is truly hypothyroid… say, in an aged cushingoid pony. But the WHOLE POINT of feeding Thyro-L to a young, healthy horse is to induce hyperthyroidism-like symptoms so they eat better and train with more energy.
This is not a new thing. This is not something silly ol’ Texarkana is making up. This is something that has been around for a VERY long time. You can disagree with it; I sure as heck do. But it’s a “thing” because enough people saw enough results to believe in it… even if you aren’t one of those people.
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Well, if a horse has a functioning thyroid, blood work will show normal T4 and stimulating hormone (TSH)- horse is “euthyroid”. If you supplement these horses with L Thyroxine, you suppress their own thyroid gland but lab results may be normal. If you over supplement, T4 goes up++ and TSH goes way low, and you get symptoms of an overactive thyroid with increased appetite, increased metabolism (with weight loss) and increased heart rate. And they are “hot” and nervous. Long-term problems may include osteoporosis, heart problems and muscle weakness It takes several months for lab work to return to normal after stopping thyroid supplements in a horse with a functionally normal thyroid.
Too little thyroid hormone (ie hypothroidism) may be a factor in metabolic syndrome, and supplementation may help to normalise weight and metabolism. If a horse is truly hypothyroid, you supplement until both T4 and TSH are normal. Appetite, weight and behaviour should be normal, horse becomes euthyroid.
If you over supplement, again you get hyperthroidism.
It really doesn’t seem to me that it would enhance performance to make them hyperthyroid, but then I do not train racehorses!
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Texarcana posted at the same time as I did. L Thyroxine is definitely not an appetite suppressant.
I must add that I am an MD, applying human endocrine principles to equines, can’t be that different!
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@demidq You and Palm Beach both seem to have taken exception to the “performance enhancing” phrase… which I blame on myself. Perhaps I should have chosen better wording… like “people believe it improves condition so horses train better.” Which to me, is enhancing performance… especially when you are replacing good horsemanship practices with pharmaceuticals to try to achieve similar results.
Thanks for the medical explanation!
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Thanks Texarkana, I didn’t mean to disagree with you. I am naively amazed at the vet approved hormonal manipulation in the name of improved performance. You have explained it well!
It’s not vet approved for improved performance. It’s vet approved for a horse that is overweight. You will be hard pressed to find a vet who recommends it for any other reason. And Tex, you don’t get to choose which symptoms of hyperthyroidism your horse exibits. If he is showing one symptom, he is at risk for all of them, including the one that makes them drop dead (a la Bob Baffert). Very few horses are low thyroid, most test will come back on the low end of normal if it is suspected. Putting a whole barn on it is just crazy and a sign of a trainer who is insecure about his or her program and willing to risk the health of the horse in the name of one more win.
@Palm Beach Your tone implies you are telling me something “I don’t know” or that I’m somehow endorsing this practice.
I’m not.
You strongly disagree with this practice. So do I. But through your posts, you have indicated you don’t have any firsthand experience with it whatsoever… just “what your vet told you.” You have also demonstrated some glaring misconceptions with how you think it works.
The OP asked about thyroid replacement in TB race horses. I told her why (some) people give thyroid replacement to TB race horses. That’s all.
The FEI also classifies levothyroxine as “performance enhancing.” Do you want to tell them what they don’t know, too?
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I have firsthand experience because my vet prescribed it for an overweight horse. I feed it to this horse daily. I don’t have “firsthand” experience with my racehorses because I disagree that it enhances performance. In post 2 you state that it increases metabolism so the horses put on weight and muscle - that just doesn’t make sense. Increaed metabolism burns calories. You put on weight and muscle by eating more and progressive loading of the muscles.
Hypothyroidism is rare in horses - some vets will say it doesn’t exist.
@Palm Beach Slowly re-read each one of my posts.
I already addressed every single criticism you are still flogging (in post 4 specifically). I even used some very similar wording to what you just said in post 19.
You can disagree with the practice yourself; I personally think it’s a crappy practice. But your fat horse with a script is not your typical TB in race training. It is not the same thing. Someone with your extensive experience in racing knows this better than anyone.
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