Serum Se will reflect both deficiencies and toxicities. Urinary Se is not diagnostic. Iron - Clinical signs of excess Fe may include those of induced Cu deficiency, recurrent bacterial infections or hepatic necrosis. Deficiency is unlikely but theoretically may cause anemia. Feed analysis is a fair measure of Fe intake, though not all forms of Fe are available for absorption and only a small proportion is absorbed.
Absorption is enhanced by low pH and ascorbic acid.
It is rare to find a forage deficient in Fe. Serum Fe is not reliable. Sepsis causes sequestration of Fe, reducing its availability to microbial populations but not the horse. Serum ferritin concentrations may reflect either deficiency or toxicity. Anemia is not a good indicator of Fe status in horses as there are many other causes of low hemoglobin and reduced red blood cells unrelated to Fe status.