Thyro-L no longer working??


My Connemara mare, now 10, weighed 1325 last year. She is 14.2. Vet put her on two tablespoons of Thyro-L per day (yes, TABLESPOONS). She quickly lost weight and got down to around 1100 in 7 months. We decreased her dosage as her T4 was high but her T3 was still low.  Her insulin was high but is now normal. She put weight on again and is now about 1250. We upped the Thyro to 2 tablespoons again a couple of months ago but she has not lost weight, in fact has gained some. She wears a grazing muzzle and gets no grain, just teff pellets, 1/2 cup of Outlast, salt, Insulinwise and supplements. I do give her NSC treat when I am clicker training her to trailer load, but not a significant amount. I I try to ride her at least 2-3 times a week for anything from half an hour to two hours on trail. Nothing in her routine now is different from when she first went on the high does of Thyro-L so I am mystified about why she is not losing weight again. I have cut the Thyro-L back to 1 T a day as she was starting to spook at everything and was getting wired, and that is not her personality at all; she's back to her old self now. Any thoughts?
Zoe Kharpertian
Landrum, SC 29356

Lavinia Fiscaletti

Hello Zoe,

Welcome to the group! 

High insulin has nothing to do with thyroid function, so supplementing thyroid meds won't solve that problem. Most members here have found no benefit from using the Insulinwise. Rather, a tightly mineral balanced diet will be key to maintaining both insulin numbers and weight. Losing weight does impact insulin levels, so your girl's weight loss was most likely the cause of her lowered levels. We really need to see exactly what all her blood work results have been to be able to be more specific. While it's a good thing that her insulin levels have dropped to within the lab's reference range, please know that these range's are not to be confused with "normal":

We also need to know her entire current diet to be able to respond more specifically to your questions. That's where a case history comes in - you should have already received info on how to complete one but if not, there are links to that info further along in this note.

Great that your girl is getting regular exercise. As you already know, a 14.2h Connemara is definitely grossly overweight at 1325lbs. For her size, I would expect her ideal weight to be no more than 900lbs - maybe less. At 2% of her ideal body weight, that would mean that she would need no more than 18lbs (forage plus any concentrates) per day to maintain a good condition. You'll need to weigh every morsel of food that passes her lips in order to find out exactly how much she is actually consuming. This includes weighing all the treats she is getting.

Thyro-L will jump start weight loss in an individual by artificially making the horse hyperthyroid. The effects are only temporary and will only last until the horse's body down-regulates natural thyroid hormone production to compensate for the excess. At best, this is a temporary fix - not meant to be a permanent solution to being overweight. If the animal is overweight, it means it is taking in more calories than it needs to maintain proper condition. The answer is to reduce the amount of intake to support the correct weight. Thyroid medication needs to be weaned off very slowly in order to allow the body to ramp up normal production, so please be very careful when stopping the thyro-L.

The remainder of this message contains our official welcome, with many links to further reading for in-depth explanations. It contains a LOT of information, which should help answer your questions, as well as prompt you to ask new ones.

The ECIR Group provides the best, most up to date information on Cushing's (PPID) and Equine Metabolic Syndrome (EMS)/Insulin Resistance (IR). Please explore our website where you'll find tons of great information that will help you to quickly understand the main things you need to know to start helping your horse. Also open any of the links below (in blue font) for more information/instructions that will save you time.

Have you started your Case History? If you haven't done so yet, please join our case history sub-group. We appreciate you following the uploading instructions so your folder is properly set up with the documents inside. Go to this CH message with info on how to use various devices and forms. If you have any trouble, just post a message to let us know where you are stuck.

Orienting information, such as how the different ECIR sections relate to each other, message etiquettewhat goes where and many how-to pages are in the Wiki. There is also an FAQs on our website that will help answer the most common and important questions new members have. 

Below is a general summary of our DDT/E philosophy which is short for Diagnosis, Diet, Trim and Exercise.


DIAGNOSIS: There are two conditions dealt with here: Cushings (PPID) and Equine Metabolic Syndrome (EMS)/Insulin Resistance (IR). These are two separate issues that share some overlapping symptoms. An equine may be either PPID or EMS/IR, neither or both. While increasing age is the greatest risk factor for developing PPID, IR can appear at any age and may have a genetic component. Blood work is used for diagnosis as well as monitoring the level of control of each.

PPID is diagnosed using the Endogenous ACTH test, while EMS/IR is diagnosed by testing non-fasting insulin and glucose.

The fat-derived hormone leptin is also usually abnormally elevated in insulin resistance but because there are many other things which can lower or increase leptin ECIR is not recommending routine testing for this hormone. Leptin is the hormone that says "stop eating".

In Europe, adiponectin is tested instead of leptin. Adiponectin helps regulate glucose and fat burning, and maintain insulin sensitivity. Low levels are associated with EMS. It has come to be preferred over leptin because it is not influenced by things like weight or exercise, and also because it was the only factor other than insulin levels that predicted laminitis risk

*Before calling your vet to draw blood for tests, we suggest saving time and wasted money by reading these details and then sharing them with your vet so that everyone is on the same page regarding correct testing and protocols.

*Please remember to request copies of the results of all the tests done rather than just relying on verbal information. Your vet should be able to email these to you. If you have previous test results, please include those as well. All should go in your CH, but if you are having any trouble with the CH, just post in the messages for now. 

Treatment: EMS is a metabolic type - not a disease - that is managed with a low sugar+starch diet and exercise (as able). The super-efficient easy keeper type breeds such as minis, ponies, Morgans, Arabs, Rockies are some of the classic examples. PPID is a progressive disease that is treated with the medication pergolide. Some, but not all, individuals may experience a temporary loss of appetite, lethargy and/or depression when first starting the medication. To avoid this "pergolide veil" (scroll down for side effects), we recommend weaning onto the drug slowly and the use of the product APF. The best long term results are seen when the ACTH is maintained in the middle of the normal range at all times, including during the annual seasonal rise. To accomplish this, the amount of medication may need to increase over time. Neither condition is ever "cured", only properly controlled for the remainder of the equine's life. If your partner is both PPID and IR then both medication and diet management will be needed. 

DIET: Almost all commercial feeds are not suitable - no matter what it says on the bag. Please see the International Safe Feeds List for the safest suggestions.

No hay is "safe" until proven so by chemical analysis. The diet that works for IR is:

  • low carb (less than 10% sugar+starch)
  • low fat (4% or less) 
  • mineral balanced  

We use grass hay, tested to be under 10% ESC + starch, with minerals added to balance the excesses and deficiencies in the hay, plus salt, and to replace the fragile ingredients that are lost when grass is cured into hay, we add ground flax seed and Vitamin E. This diet is crucial for an EMS/IR horse, but also supports the delicate immune system of a PPID horse. 

*Until you can get your hay tested and balanced we recommend that you soak your hay and use the emergency diet (scroll down for it).  The emergency diet is not intended for long term use, but addresses some of the most common major deficiencies. Testing your hay and getting the minerals balanced to its excesses and deficiencies is the best way to feed any equine (look under the Hay Balancing file if you want professional help balancing). If you absolutely cannot test your hay and balance the minerals to it, or would like to use a "stop gap" product until you get your hay balanced, here's a list of "acceptable" ration balancers

There is a lot of helpful information in the start here folder so it is important you read all the documents found there. The emergency diet involves soaking your untested hay for an hour in cold water or 30 minutes in hot water. This removes up to 30% of the sugar content, but no starch. Starch is worse than sugar since it converts 100% to glucose while sugar only converts 50%, so starch causes a bigger insulin spike. Make sure you dump the soaking water where the equine(s) can't get to it. 

What you don't feed on the EMS/IR diet is every bit as, if not more important than, what you do feed! No grass. No grain. No sugary treats, including apples and carrots. No brown/red salt blocks which contain iron (and sometimes molasses) which interferes with mineral balancing, so white salt blocks only. 

No products containing molasses. No bagged feeds with a combined sugar and starch of over 10% or starch over about 4%, or fat over about 4%. Unfortunately, even bagged feeds that say they are designed for IR and/or PPID equines are usually too high in sugar, starch and/or fat. It’s really important to know the actual analysis and not be fooled by a name that says it is suitable for EMS/IR individuals.

We do not recommend feeding alfalfa hay to EMS/IR equines as it makes many of them laminitic. Although it tends to be low in sugar, many times the starch is higher and does not soak out. Additionally, protein and calcium are quite high, which can contribute to sore footedness and make mineral balancing very difficult.

TRIM: A proper trim is toes backed and heels lowered so that the hoof capsule closely hugs and supports the internal structures of the foot. Though important for all equines, it's essential for IR and/or PPID equines to have a proper trim in place since they are at increased risk for laminitis. After any potential triggers are removed from the diet, and in PPID individuals, the ACTH is under control, the realigning trim is often the missing link in getting a laminitic equine comfortable. In general, laminitic hooves require more frequent trim adjustments to maintain the proper alignment so we recommend the use of padded boots rather than fixed appliances (i.e. shoes, clogs), at least during the initial phases of treatment.

Sometimes subclinical laminitis can be misdiagnosed as arthritis, navicular, or a host of other problems as the animal attempts to compensate for sore feet. 

You are encouraged to make an album and post hoof pictures and any radiographs you might have so we can to look to see if you have an optimal trim in place. Read this section of the wiki for how to get a hoof evaluation, what photos are needed, and how to get the best hoof shots and radiographs.

EXERCISEThe best IR buster there is, but only if the equine is comfortable and non-laminitic. An individual that has had laminitis needs 6-9 months of correct realigning trims before any serious exercise can begin. Once the equine is moving around comfortably at liberty, hand walking can begin in long straight lines with no tight turns. Do not force a laminitic individual to move, or allow its other companions to do so. It will begin to move once the pain begins to subside. Resting its fragile feet is needed for healing to take place so if the animal wants to lay down, do not encourage it to get up. Place feed and water where it can be reached easily without having to move any more than necessary. Be extremely careful about movement while using NSAIDs (bute, banamine, previcox, etc.) as it masks pain and encourages more movement than these fragile feet are actually able to withstand. Additionally, NSAIDs (and icing) do not work on metabolic laminitis and long term NSAID use interferes with healing. Therefore, we recommend tapering off NSAIDs after the first week or so of use. If after a week's time your equine's comfort level has not increased, then the cause of the laminitis has not been removed and keeping up the NSAIDs isn't the answer - you need to address the underlying cause.


There is lots more information in our files and archived messages and also on our website. It is a lot of information, so take some time to go over it and feel free to ask any questions. If you are feeling overwhelmed, don't worry, you will catch on, and we are always here to help you! Once you have your case history uploaded, we can help you help your equine partner even better.

For members outside North America, there are country specific folders in the files and many international lists in the wiki to help you find local resources.

If you have any technical difficulties, please let us know so we can help you.

Lavinia, George Too, Calvin (PPID) and Dinky (PPID/IR)
Nappi, George and Dante Over the Bridge
Jan 05, RI
Moderator ECIR

Eleanor Kellon, VMD

I know the welcome messages are long and overwhelming so to just boil down what Lavinia said to the weight issue - she is eating too much. You should have her on hay weighed to 2% ideal weight or 1.5% current weight (whichever is larger) and zero pasture. Seal the muzzle. Her Thyro-L will have to be weaned slowly because it has been suppressing her normal thyroid output but once you get a correctly balanced diet, especially selenium and iodine for thyroid, you can do that. Up the exercise as much as you can.
Eleanor in PA 
EC Owner 2001
The first step to wisdom is "I don't know."