1.4.51 अकथितश्च

When an object is गौण (i.e. not said/counted as any other case -संप्रदान अपादान etc.) then कर्म is implied. For example, in देवः गां पयः दोग्धि,  गां has कर्म due to गौण status. Without गौण status, देवः गोः पयः दोग्धि (अपादान effective).