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Marker in livestock nutrition experiments
Natural dried, not calcined diatomaceous earth is regularly used in livestock nutrition research as a source of acid insoluble ash (AIA), which is used as an indigestible marker. By measuring the content of AIA relative to nutrients in test diets and feces or digesta sampled from the terminal ileum (last third of the small intestine) the percentage of that nutrient digested can be calculated using the following equation:


 * $$N = \left ( 1 - \frac{N_f}{N_F} \right ) \times \left ( \frac{A_F}{A_f} \right ) \times 100 $$


 * Where:
 * N is the nutrient digestibility (%)
 * Nf is the amount of nutrients in the feces (%)
 * NF is the amount of nutrients in the food (%)
 * Af is the amount of AIA in the feces (%)
 * AF is the amount of AIA in the food (%)

Natural freshwater diatomaceous earth is preferred by many researchers over chromic oxide, which has been widely used for the same purpose, the latter being a known carcinogen and, therefore, a potential hazard to research personnel.