To inexpensively obtain an additive successively reducing organic load of animal feces on environment and enhancing its decomposing properties, preventing pollution by residual feed.

This additive comprises seashell fossil which is a crystal having soluble humus produced by accumulation of buried various nektons comprising calcareous, silicic acid or the like, planktons, algae or the like, as the active component and successively reduces the organic load of animal feces on environment and feeds. Since the minerals in the additive are absorbed by animals and enhances their physiological activities, retains sufficient healthy state and the components in the feed to be changed into meat and blood, are sufficiently digested and absorbed to reduce the organic materials in the feces, can reduce the organic load on the environment and increase self decomposing properties of the feces, the additive enables inexpensively reducing the pollution of fishing spot in water area and of feedlot on land, and prevent environmental pollution caused by an environment cleaning agent in remaining feeds, retard the progress of the aging of a fishing spot due to self pollution, make close to the natural decontamination capacity and inhibit no more aging of the fishing spot.