This is an archived Horseadvice.com Discussion. The parent article and menus are available on the navigation menu below:
HorseAdvice.com » Diseases of Horses » Endocrine System » Hypothyroidism in Adult Equines »
  Discussion on Research Summary: Thyroid Supplementation for Weight Control?
Author Message
Moderator:
DrO

Posted on Monday, Feb 11, 2008 - 7:56 am:

As long time readers are aware I have constantly fought against the notion that overweight cresty horses are hypothyroid and that attention to diet not hormone supplementation is the way to deal with this problem. But, does thyroid supplementation of the euthyroid (normal thyroid) horse help with weight control? In other species hyperthyroidism is a serious disease, so is over supplementation harmful to the horse?

Here are two studies that did find there was weight loss, increased insulin sensitivity, and did not find ill effects for several parameters of health at least for the 48 wk course of the experiment. I should note that when I first started practising there were many horses on thyroid supplementation for obesity and for the most part they were still obese and having bouts of spring founder. Diet was the way we eventually got these horses under control. So stay tuned, it appears they had some confounding variables in the efficacy experiment and they feel further work needed. If thyroid supplementation significant helps for controlling obesity while not impairing the health of the horse holds up this will be good news for those struggling with this all too common problem of the modern horse.
DrO

Am J Vet Res. 2008 Jan;69(1):76-81.

Effects of long-term oral administration of levothyroxine sodium on glucose dynamics in healthy adult horses.

Frank N, Elliott SB, Boston RC.

Department of Large Animal Clinical Sciences, College of Veterinary Medicine, University of Tennessee, Knoxville, TN 37996.

Objective-To determine the effects of long-term oral administration of levothyroxine sodium (L-T(4)) on glucose dynamics in adult euthyroid horses. Animals-6 healthy adult mares. Procedures-Horses received L-T(4) (48 mg/d) orally for 48 weeks. Frequently sampled IV glucose tolerance test procedures were performed on 3 occasions (24-hour intervals) before and at 16, 32, and 48 weeks during the treatment period. Data were assessed via minimal model analysis. The repeatability of measurements was evaluated. Results-During treatment, body weight decreased significantly from the pretreatment value; mean +/- SD weight was 49 +/- 14 kg, 43 +/- 7 kg, and 25 +/- 18 kg less than the pretreatment value at weeks 16, 32, and 48, respectively. Compared with pretreatment findings, 1.8-, 2.4-, and 1.9-fold increases in mean insulin sensitivity (SI) were detected at weeks 16, 32, and 48, respectively; SI was negatively correlated with body weight (r = -0.42; P < 0.001). During treatment, glucose effectiveness increased and the acute insulin response to glucose decreased. Overall mean within-horse coefficients of variation were 5% and 29% for plasma glucose and serum insulin concentrations, respectively, and 33%, 26%, and 23% for SI, glucose effectiveness, and the acute insulin response to glucose, respectively. Conclusions and Clinical Relevance-Long-term administration of L-T(4) was associated with weight loss and increased SI in adult euthyroid horses, although other factors may have confounded results. Levothyroxine sodium may be useful for the treatment of obesity and insulin resistance in horses, but further studies are required.

Am J Vet Res. 2008 Jan;69(1):68-75.

Effects of long-term oral administration of levothyroxine sodium on serum thyroid hormone concentrations, clinicopathologic variables, and echocardiographic measurements in healthy adult horses.

Frank N, Buchanan BR, Elliott SB.

Department of Large Animal Clinical Sciences, College of Veterinary Medicine, University of Tennessee, Knoxville, TN 37996.

Objective-To determine the effects of long-term oral levothyroxine sodium (L-T(4)) administration on serum thyroid hormone concentrations, thyroid gland function, clinicopathologic variables, and echocardiographic examination measurements in adult euthyroid horses. Animals-6 healthy adult mares. Procedures-Horses received L-T(4) (48 mg/d) orally for 48 weeks. Every 4 weeks, physical examinations were performed; blood samples were collected for CBC, plasma biochemical analyses, and assessments of serum total triiodothyronine (tT(3)) and thyroxine (tT(4)) concentrations. Plasma creatine kinase MB activity and cardiac troponin I concentration were also measured. Echocardiographic examinations were performed before and at 16, 32, and 48 weeks during the treatment period. Results-During the treatment period, mean body weight decreased significantly; heart rate varied significantly, but the pattern of variation was not consistent. Significant time effects were detected for certain clinicopathologic variables, but mean values remained within reference ranges. Cardiac troponin I was only detectable in 8 of 24 plasma samples (concentration range, 0.01 to 0.03 ng/mL). Serum creatinine kinase MB activity did not change significantly over time. Compared with the pretreatment value, 5.4-, 4.0-, and 3.7-fold increases in mean serum tT(4) concentrations were detected at 16, 32, and 48 weeks, respectively. Some cardiac measurements changed significantly over time, but mean values remained within published reference ranges. Mean fractional shortening was lower than the pretreatment mean value at 16 and 32 weeks. Conclusions and Clinical Relevance-In horses, long-term oral administration of 48 mg of L-T(4)/d significantly increased serum tT(4) concentrations and did not appear to adversely affect health.
Home Page | Top of Page | Join Us!
Horseadvice.com is a BBB Accredited Business. Click for the BBB Business Review of this Horse Training in Stokesdale NC