What is difference between primary and secondary nutritional deficiencies?

A primary nutritional deficiency is caused by a simple lack of the nutrient in the diet. For instance, cats that are fed strictly fish develop a primary taurine deficiency because the fish don't have enough taurine in them. A secondary nutritional deficiency is caused by another disease process limiting the amount of the nutrient available to the body. For instance, a cow may develop secondary B12 deficiency if it eats too much of certain weeds that have a vitamin B12-destroy enzyme.