21 C.F.R. § 573.320
The food additive diammonium phosphate may be safely used in ruminant feed in accordance with the following prescribed conditions:
(a) The food additive is the product resulting from the neutralization of feeding-phosphoric-acid or defluorinated wet-process phosphoric acid with anhydrous ammonia. It contains not less than 106.25 percent equivalent crude protein (nitrogen × 6.25) and 20 percent phosphorus. It contains not more than the following:
1 part fluorine to 100 parts phosphorus. 75 parts per million or arsenic (as As). 30 parts per million of heavy metals, as lead (Pb).
(c) To assure safe use of the additive, the label and labeling of the additive and that of any feed additive supplement, feed additive concentrate, feed additive premix, or complete feed prepared therefrom shall contain, in addition to other information required by the act, the following: