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RE: [RC] Hypothyroid & Anemia - heidiAs you may guess by the subject, I have a rather sick horse. He is on the mend, thank goodness. Short version, I noticed he seemed listless and lethargic. He was EDPP, but he tired easily and took longer than usual to recover from activity. I called the vet out (the irony at this point is, after he was looked at, everybody at the ranch was telling me how they saw my horse laying down a lot -- that would've been nice to know sooner, folks....), who couldn't find anything obviously wrong. So, we drew a blood panel. A few days later, vet called and said the horse was anemic, and hypothyroid. So, he's on a high-iron supplement (red cell) and thyroid medication. Now my questions is this: does anybody know if levothyroxin (the thyroid med he's on) will disqualify him from endurance? If I have to take him off of it to compete, how long do I withdraw it before a ride? If he ends up taking this for life, and he'd have to go off it to compete, I will very likely retire him from the sport. Sad, really, since he loves it. Yes, levothyroxin is a "drug" and as such would not be legal in competition. And given the metabolic issues of being hypothyroid, it would not be fair to him to take him off of it to compete. That said, supposedly primary hypothyroidism does not occur in horses. So being hypothyroid is a sign that there is something else going on. Often hypothyroidism is a precursor to Cushings disease and/or insulin resistance. I've seen a couple of horses that presented as hypothyroid that with careful dietary management and VERY regular riding have been able to get off of the levothyroxin and compete. So you might want to think about that. Try getting him on a very low sugar diet (if he isn't already) and have his exercise regimen be like clockwork. Regarding anemia, don't assume that it is due to iron deficiency without testing iron levels. Iron toxicity can also cause anemia, as can a whole host of other problems. I'd sure be looking at some other cause for the anemia... From Merck veterinary manual: Iron: Iron deficiency may be secondary to parasitism or chronic blood loss and results in microcytic, hypochromic anemia. However, it is highly unlikely that even anemic horses are iron deficient. Iron excess interferes with copper metabolism and also causes microcytic, hypochromic anemia. Blood transferrin concentrations are the most reliable method to determine the iron status of a horse. From NUTRIENT REQUIREMENTS OF HORSES, 5th revised edition: Iron The body of a 500-kg horse contains about 33 g of iron. This is distributed in hemoglobin (60 percent), myoglobin (20 percent), storage and transport forms (20 percent), and cytochromic and other enzymes (0.2 percent) (Moore, 1951). Forage and by-product ingredients commonly contain 100 to 250 mg of iron/kg. Grains usually contain less than 100 mg/kg. Dietary iron absorption in nonruminants fed adequate iron is likely to be 15 percent or less. Iron utilization increases in iron-deficient diets and diminishes with higher than normal intakes of cadmium, cobalt, copper, manganese, and zine (Underwood, 1977). Daily endogenous losses of iron have not been reported for horses, and their dietary iron requirement has not been researched specifically. The iron requirement is estimated to be 50 mg/kg of diet for growing foals or pregnant and lactating mares and 40 mg/kg of diet for mature horses. Common feedstuffs, therefore, should meet the iron requirements. According to Meyer (1986), approximately 37, 38, and 92 mg of iron are deposited each day in the fetus and membranes during months 9, 10, and 11 of gestation, respectively. In a 500-kg mare, this translates to 74, 76, and 184 µg/kg of mare weight. The iron content of mare's milk ranges from 1.3 µg/g at parturition to 0.49 µg/g at 4 months postpartum (Ullrey et al., 1974). A mare producing 15 kg of milk/day would require approximately 130 mg of iron daily for early lactation and 32.6 mg of iron for 10 kg of milk/day in late lactation, in addition to the iron requirement for maintenance. Serum ferritin, an accurate measure of iron status, ranged from 70 to 250 ng/ml with a mean of 152 ± 54.6 for normal horses (Smith et al., 1984). Signs of Deficiency or Excess: The primary signs of iron deficiency are microcytic and hypochromic anemia. Although young, milk-fed foals are most susceptible to this anemia, iron deficiency is not a practical problem in foals or mature horses at any performance level. This is true, in part, because the body efficiently salvages and retains iron derived from the catabolism of body constituents. Various iron supplements, under natural feeding programs, have been ineffective in improving the hemoglobin or oxygen-carrying capacity of red blood cells (Kirkham et al., 1971). 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