A nutritional deficiency may be due to a nutrient being omitted from the diet, adverse interaction between nutrients, or interaction between nutrients and specific antinutrients. The latter situations are difficult to diagnose, because on analysis the diet is found to contain a normal level of the nutrient under study. Micronutrients are often added to diets in the form of premixes, so it is rare to see classic individual deficiency symptoms—the effect is more commonly a compilation of many individual metabolic conditions. In many instances, a correct diagnosis can be made only by obtaining complete information about diet and management, clinical signs in the affected living birds, necropsies, and tissue analyses.
A diet that, by analysis, appears to contain just enough of one or more nutrients may actually be deficient to some degree in those nutrients. Stress (bacterial, parasitic, or viral infections; high or low temperatures; etc) may either interfere with absorption of a nutrient or increase the quantity required. Thus, a toxin or microorganism, for example, may destroy or render unavailable to the bird a particular nutrient that is present in the diet at apparently adequate levels.
Last full review/revision March 2012 by Steven Leeson, PhD