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  Discussion on Hypothyroidism in foaling mares
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Posted on Sunday, Apr 25, 1999 - 8:42 am:

I am looking for more info (any references would be great) on hypothyroidism is broodmares.

While we have not conducted any proper experiments, I have noticed some interesting (apparent) correlations. We have had a handful of mares tested for T4 levels over the past few years. These mares either would not ovulate, wouldn't cycle well, did not produce milk until after foaling, had dystocias and complications, or
became very thin in the last weeks of pregnancy or shortly after foaling. The thin mares feed had been increased during the last trimester and again after foaling. According to our vet, the mares tested in the low end of the normal range (1.4,1.6,1.8). He thinks a broodmare should test over 2.0 (I think units are mg%, but not given on lab result). Our observations support his position, although we have not yet tested the normal mares.

We also use water hardness test strips to monitor the level of Ca+ in the mare's udder secretions prior to foaling.(EM Quant Total Hardness Test strips). A reading of 4 blocks indicates a level of over 370 ppm. The research indicates (reference missing) that once mares reach this level, that 80% of them will foal within 24-48 hours. My observations until this year agreed. The average interval of 25 foalings was 2 days. No mare but one, had hung at 4 blocks for over 4 days.

This year, Jessie, a mare that had a low T4 level in the past, hung for 7 days. She was receiving a levothyroxine supplement, but had not been tested to be sure the dose was adequate (circumstance beyond my control). I suspect it was not. Her skin and coat did not look good at the end of that week. She had rubbed the hair out on her hip and she was losing weight. She had a uterine prolapse 72 hrs. post foaling and had to be euthanized. (Mare had prolapsed 3 yrs. prior but had successfully foaled last year).

The second mare this year hung at 4 blocks for 9 days. There was nothing wrong with the test strips, we checked. This mare became very thin very quickly and did not look well after foaling. Her foal died due to a dystocia. A hind foot was caught up on the pelvic rim. It was repositioned, but then we had a case of hip lock for 9 minutes. Five people were required to remove the foal. The vet talked us through it on the phone. I can't help but wonder if she had foaled when the Ca+ test indicated the foal was ready, if the foal would have been smaller enough to fit more easily. Her T4 test was 1.8. She is the adoptive mom of the first mare's orphan. She is doing much better now that she is on a levothyroxine supplement.

Now, there is another mare that has been at 4 blocks for 4.5 days. She also lost a lot of weight in the last two weeks and she is being fed well. Needless to say, I am very concerned. She will be tested tomorrow for T4.

Any insight would be greatly appreciated. The article here on hypothyroidism mentioned environmental causes. I would like to know what kind of things these causes might be. I understand that true hypothyroidism is rare in horses, but what about environmentally induced hypothyroidism? Or potential causes of low normal readings like in my mares? It seems like they are fine until they have to maintain the higher metabolic rate of late gestation and lactation.

Posted on Monday, Apr 26, 1999 - 7:48 am:

Hello again Sarah,
Hypothyroidism of any cause is rare in adult horses and the scientific, medical, and veterinary literature is all but void of proven cases. So rare that everything we know about clinical signs of hypothyroidism in the adult horse comes from experimental thyroidectomy.

In spite of this some veterinary writers were trying to make the case for this "possibly" being a common problem as recently as 10 years ago, but this has stopped. As recently as 3 years ago some where conjecturing this may be a undiagnosed cause of..you pick the performance problem, but at least they are now saying their conjectures, so far, are poorly documented.

As the article states measuring T3 and T4 levels but does accurately assess thyroid function. To test thyroid function you must do a TSH test.
[Am J Vet Res 1993 Jan;54(1):52-5
Serum triiodothyronine, total thyroxine, and free
thyroxine concentrations in horses.
Sojka JE, Johnson MA, Bottoms GD
Department of Veterinary Clinical Sciences, Purdue University School of Veterinary
Medicine, West Lafayette, IN 47907.]

I would start with asking the vet for copies of any recent work to support his contention of where T3 and T4 levels of periparturient mares should be, I know of no such work and if it exists I would like to include the references. I can find no correlation of pregnancy and T3 or T4 levels in the horse, but I can find that high energy and high protein diets, like those a horse ought to be on in late pregnancy, decrease T3 and T4 levels.

Look at your post carefully Sarah. The attempt to correlate low thyroid activity to the problems is bent to the point of breaking as given by this example: Even though one mare was supplimented with levothyroxin, she had what appears to be the worse time of it. You conjecture, she was not receiving enough.

Now lets look at another statement:
"She also lost a lot of weight in the last two weeks and she is being fed well." In a horse that is otherwise healthy this statement is inconsistant. Now I know you are trying to make the argument "that they are not healthy, they are hypothyroid." But there is nothing in the literature to support your proposition. Since you have had this weight loss in the last month several times I suggest you are not compensating enough, or properly, for the increase in nutritional needs: energy, protein, calcium, phosphorous and possibly some vitamins.

Can I say with certainty that you do not have some really odd circumstane making your horses hypothyroid? No, of course not. But the chances are so remote that I think it is far more likely you are doing harm concentrating on this rather than far more likely causes. Healthy horses that are rapidly loosing weight are not getting enough high quality groceries. 95% of the time it is just that simple and it is a problem I see all the time. There is another problem with your experimenting, we do not know the effects of thyroid supplimentation in the normal horse. We suspect it would suppress normal thyroid function, possible that of the neonate too: hypothyroidism is a documented problem in the newborn.
DrO

Posted on Saturday, Feb 26, 2000 - 11:04 am:

My mare just foaled 2/22/00 and the resulting foal has a tennis ball size goiter. The mare was on Thyrol L throughout her pregnancy. She was "diagnosed" several years ago and has been on Thyroid medication. I have had her T4 checked in May 99 and again in July 99, resulting in an increase of 1/2 scoop..total 2 scoops a day, which looks to be about 1 tsp+ I am at a loss as what to do next. I will keep her in a stall to protect the carpal and tarsal bones from becoming flat. Please give me steps to do to turn around this condition...if possible.

Judy

Posted on Sunday, Feb 27, 2000 - 8:07 am:

Judy,
Instead of posting your question at the bottom of someone elses discussion you should create your own. You will get more responses and it helps others find related information better.

Before you post a new forum discussion be sure to review the already existing articles and forum discussions on your subject. This is the appropriate topic for your subject, so just back up to your topic using the navigation bar at the top of this page and select the approriate article.

If after reviewing the already existing resources your question remains unanswered go to the closest topic and post to that forum by clicking on, "New Discussions" and choose a title that is descriptive.
Thank You,
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