All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
If you vowed to slaughter or feed the needy and the poor, then you are required to fulfill the vow. It is invalid in the Sharee'ah to slaughter only one animal with the intention of offering Udh-Hiyyah and fulfilling a vow. Vowing and offering Udh-Hiyyah are two independent acts of worship and both are intended by itself. Neither of them is included in the other. So they should not be combined in a single intention.
Allaah Knows best.