Hypothyroidism in Horses

[Louise]

OK, I did a dumb. Not the first time, won’t be the last.

My old gal, Lexy, has been on Thyro-L since before I got her in February. She is on a very low dose, and what she had when I got her has lasted all this time. My barn owner informed me about a month ago that she was running low. I noted that fact, and promptly forgot about it until I got a call last night that she was totally out. I feel very foolish and it only confirms that I need to write things down immediately, or they completely fly out of my mind.

On trying to order it, I discovered that it is a prescription product, and that SmartPak will be out until Sept. 12. I’ve emailed the vet and asked for a prescription.

However, I was prompted to do some on-line research about the product, its use, and symptoms of the hypothyroidism that it is supposed to help prevent. In this research that I did, I find it said in a couple of articles that it’s greatly over-diagnosed. One article even claims that it is nonexistent in horses.

So, now I’m wondering why she’s on the product, and if she really needs to be? I’m going to call the vet tomorrow, and, probably, have her tested to see what her current status is, and what, if anything, needs to be done. In which case, it might be a good thing for her to be off of medication for a while before testing.

I would appreciate any words of wisdom that you all can give my about hypothyroidism. I’m trying to get as educated as I can, from as many different sources as possible, before I talk to the vet tomorrow.

Thanks.

[grayarabpony]

Most horses on thyroid replacement are insulin resistant. Being IR affects thyroid production. When my pony foundered last fall her T4 was low.

Try to get your mare back on the med as soon as possible because discontinuing the medication suddenly can make her acutely hypothyroid. Your vet will probably have it in stock if Smartpak can’t get it to you right away.

[deltawave]

Another COTHer posted this link the other day and I swear I’ve seen this article floating around elsewhere. I found it very rational and reasonable and to contain some very good information.

http://www.animavet.com/ThyroidHormones.pdf

[Louise]

@grayarabpony;6518903

Most horses on thyroid replacement are insulin resistant. Being IR affects thyroid production. When my pony foundered last fall her T4 was low.

Try to get your mare back on the med as soon as possible because discontinuing the medication suddenly can make her acutely hypothyroid. Your vet will probably have it in stock if Smartpak can’t get it to you right away.

Thanks for this. I will see what the vet has to say about this problem when I call tomorrow. I can certainly make a run to the vet to pick up some, if I have to. I do know that Lexy is not Cushinoid, nor is she IR. I had her tested for both in the couple of months after I got her.

deltawave, thanks for that article. It looks very helpful. I have skimmed it and will go back and study it in more detail.

[deltawave]

Absent a diagnosis of IR/Cushings, a lot of people use Thyro-L simply as a “weight loss” supplement. Including on themselves. :no:

[cute_lil_fancy_pants]

A very respected equine internal medicine veterinarian who studies metabolic syndrome (insulin resistance) in horses at a university referral hospital told me there has never been a reported case of hypothyroidism in horses and horses with metabolic syndrome should not be placed on thyro-L for any longer than just a few weeks, and should be tapered off of it carefully so as not to cause iatropgenic hypothyroidism from the exogenous thyroid supplement.

[cute_lil_fancy_pants]

I should say: adult horses, foals are a different story. Sick euthyroid is a different story as well.

[cute_lil_fancy_pants]

From:
http://www.lamavt.com/LamaNewsLetter.pdf
Myth of Equine Hypothyroidism
Spring 2012
A number of metabolic and endocrine disorders of
the horse can have similar clinical signs such as obesity,
dry scaly skin, a long coat, poor performance or a history
of infertility and a dull lethargic attitude. The first thing a
veterinarian would do when presented with a horse
having these clinical signs is bloodwork to look for the
cause. The results of a simple blood chemistry profile
might, in fact, confirm a lower than normal concentration
of the two major thyroid hormones in horses—T3 and T4.
Horses such as these would typically be treated with a
supplemental thyroid hormone and periodic blood
monitoring. Most horses respond to this treatment by
having more energy, better attitudes and an improved body condition.
The problem we encounter when presented with low thyroid values is that various diseases and conditions
outside of the thyroid gland can also affect these thyroid values. Common diseases such as viral respiratory
infections, digestive disturbances and colic can all affect thyroid hormone concentration as can different
feeding patterns, transport and training stress and changes in body composition such as weight loss or
obesity. This presents an enormous challenge to practitioners.
There is no scientific study to support that low thyroid hormone concentrations negatively impact the
health of horses or that supplementation is necessary. The detection of low levels of thyroid hormones in
the blood is not the same as hypothyroidism. The major issue with measuring thyroid hormones is that
concentrations vary over time (within the same individual horse) and respond to many different environmental
and medical conditions. Horses with clinical signs or syndromes traditionally associated with hypothyroidism
can often have normal thyroid function. Whereas, horses with some diseases, such as Cushing’s,
can have low thyroid values. Therefore, diagnosing hypothyroidism requires carefully evaluating the patient
for other potential endocrine or metabolic problems before starting long-term thyroid hormone supplementation.
An additional test available in human medicine is a measure of thyroid stimulating hormone (TSH).
Elevated TSH concentrations in people with clinical signs of hypothyroidism provide a more accurate and
scientifically valid diagnosis. Response to TSH is also used as an indicator of thyroid function. TSH testing for
horses is difficult and expensive, making this type of thyroid testing more problematic in the horse. When
this more advanced diagnostic test is used it becomes clear that true hypothyroidism is a very rare endocrine
disorder in the horse.
Clinically, some obese horses with poor coats and lethargic attitudes have low T3 and T4 concentrations
and actually seem to do better on thyroid hormone supplementation. How does science account for
these animals? Researchers acknowledge that these overweight, likely insulin-resistant horses that possibly
have metabolic syndrome and those with Cushing’s disease and other conditions can show decreased thyroid
hormone concentrations.
Studies seem to indicate that it is highly unlikely that true hypothyroidism exists in horses. Continued
research and advanced diagnostics may further clarify this debate, but for now, equine practitioners may
have to change their mindsets and cease to see hypothyroidism as a disease requiring intervention and
search for other causes for low thyroid values on bloodwork. Thyroid hormone supplementation has been
commonly used in equine veterinary medicine. It has been advocated for anhidrotic (non-sweating) horses
and as a means of increasing fertility in broodmares and stallions. In many cases, both veterinarians and
owners would agree that positive results are seen with the addition of thyroid hormones. Thyroid hormone
supplementation does have some pharmacologic effect on horses, and research shows that levothyroxine
induces weight loss and increases insulin sensitivity.
Courtesy of Kenneth L. Marcella, DVM, DVM Magazine, 2011
For complete article, visit: DVM360.com

[Louise]

This is getting a little scary. She’s only on 1/3 of a scoop now, which is a very low dose, I’m told. I don’t know why she was put on it, and have just been continuing it because I figured it was needed. That wasn’t bright of me, but I thought it was just some little prevention thing. I’m anxious to talk to the vet after reading these replies.

Thanks so much for all who have answered so far.

[deltawave]

That’s virtually a homeopathic dose for a full-sized horse. I wouldn’t worry about it much WRT weaning a dose that small. Maybe just use what you have left, give 1/3 scoop every other day then every 3rd day and then just stop it.

(here I am assuming by “scoop” you mean the one that came with the product.)

[cute_lil_fancy_pants]

If you test the majority of horses that are experiencing an acute laminitic episode they will have low T4 (thyroid). This does not mean they are hypothyroid. The pain and inflammation from the laminitic episode results in the low T4, known as sick euthyroid syndrome- these horses do not need thyroid supplementation!

[Louise]

She foundered when she was seven, while in foal. She’s 26 now and has never had another episode. I had her feet x-rayed, also, after I got her, because I wanted to see if that long ago founder had left any residual damage. None whatsoever, no rotation.

Everyone has been very helpful, and I now have a lot of questions to ask tomorrow. It’s a long drive to the vet’s office from where I live, but I’ll make it gladly, since it was my forgetfulness that caused her to be completely out. I just want to make sure that the vet has some there, before I head out. I’ll put her right back on the Thyro-L. She’ll only have missed one day. Then, I’ll find out if she does, indeed need to be on the stuff. It sounds like, maybe not. If that’s the case, I’ll wean her the correct way.

And, yes, deltawave, it’s the scoop that comes with the meds.

[deltawave]

I have put my Shetland on it a couple of times (she is clinically borderline IR) to get some weight off her and normally use 1.5 scoops. I wean her down to half a scoop daily, then half every other day and then off–your 1/3 of a scoop for a full-sized horse probably does not need any weaning at all. If she sneezes while eating it probably blows away! :lol: I’m not sure there IS a proper protocol, but of course ask your vet and see what they say. I wouldn’t sweat it too much, though.

[grayarabpony]

Clfpp the T4 supplementation is a supportive therapy. While not clinical hypothyroidism the levels of thyroid hormones are still low, and supplementation does help the horse.

Speaking of IR horses – not Louise’s horse – the fact of the matter is that even with careful management a horse is in danger of another laminitic episode. Supplementing T4 will not prevent laminitis if the horse gets too heavy – which they can, even with the T4 – but who knows, it may lessen the severity of the laminitic episode. My vet has seen good results with horses that stay on it. I’ve been afraid to take my horse off because the grass was good all winter (very mild weather) and has stayed good all year.

Louise it sounds like your vet will say your horse doesn’t need to stay on the med long term and agree with delta that she is on a really small dose.

[NorCalDressage]

Horses seem to get hypothyroid as a secondary effect of Insulin Resistance. But Thyro-L increases insulin sensitivity & therefore can be beneficial for IR horses beyond helping them loose weight.

I don’t see why you would take a truly IR horse off Thyro-L. That said, it doesn’t sound like this mare has that problem & 1/3 of a teaspoon of Thyro-L is going to do basically zilch for an adult horse, IMO.

[Louise]

Vet called, and waiting a return call. Car is gassed up and ready to go. Once again, I am grateful to all of those who responded. Thank you! I’ll let you all know what the vet says.

[heidi6271]

IR/Cushings Feeding & Exercise Confusion - Help!

Hi All - Long time COtH subscriber, first time forum poster…I have a 20 yr KWPN gelding who foundered on grass 3 yrs ago. Has been on Thyro-L,up to 3 scoops a day, now at 1, and “low starch” diet ever since. (My vet tells me all equine thryoid meds are back ordered indefinitely, btw) My horse is now looking underweight to me (ribby, hip bones protruding, etc).
I’m trying to put weight back on safely for the winter by feeding more soaked hay -husband complains about the mess - and adding WellSolve (2 cups/day). He also gets a cup of whole oats, 1.3 cups of extruded soy and 1.3 cups rice bran mixed into soaked beet pulp 2 x/day and Pergolide, Remission and Strongid supplements. I have been doing some more reading and am now concerned about feeding rice bran and whole oats at all (my vet told me to) because of high NSC content. I also know I should be riding him, but he does not seem to have much interest in working, so I feel badly that I may be causing him pain by riding, but I also see that he’s losing muscle, which I know isn’t good either…
Any help/suggestions are welcome. Also any creative ideas for soaking and draining hay with less mess and in the winter time would be appreciated!

[Louise]

Just to let all of you who were so helpful know, the vet was out today. She agrees that we can probably take her off of the Thyrol L. It seems that she has been on this very low dose for a long time, and that, when she was put on it, the protocol was different. Now, as you guys said, there is a better understanding about the condition (mainly, that it hardly ever exists). We’re running a thyroid test, just to make sure, and then we will be weaning her from the medication.

Just as a side note, I’ll bump the Lexy thread on Off Course with more detail, the vet also had some very nice things to say about her condition. I came away from the exam feeling like a million dollars.

[Wyomingrider]

My 10 year old has had laminitis twice this winter. Each time temps plunged below zero for several days. Long story, but we’re treating her for hypothyroidism while we await test results.
while new to dealing with laminitis, I 've struggled with getting adequate treatment for hypothyroidism for years. I see similarities to horses in winter laminitis. 1.) Raynaud’s syndrome in people is often caused by hypothyroidism. When cold, a person will experience constricting blood vessels in fingers, sometimes toes too, with Raynauds syndrome. It can be painful and makes one susceptible to frostbite. The symptoms disappear when hypothyroidism treatment is optimized. 2.) Hypothyroidism is poorly treated generally in people, can’t imagine it’s any better in horses. There’s even a movie about it, Sick to Death. And numerous websites helping those who have it. mary Shomon, is one of many thyroid advocates for better treatment. Anyway. I’ve found the my TSH can be at the lowest end of the range, yet I’m very symptomatic. When more extensive tests are run, my Free T3 is very low or my Reverse T3 is very high, interfering with metabolism of the thyroid hormone. Additionally if my progesterone levels are too low, or estrogen too high it interfers with my thyroid levels.
im convinced winter laminitis is Raynauds Syndrome in horses caused by hypothyroidism and a simple TSH test won’t tell you that. If a mare, I suspect female hormone levels are messing with the thyroid hormone levels.