Altogether seven (domestic) and seven (wild animals are declared fit for sacrifice. Instead of all being equally fit, each succeeding one is inferior to the preceding one. The Vedas again say that the whole universe is appointed for sacrifice. The Vedas have appointed Purusha for the same purpose.
तदन्योन्यवराः सर्वे प्राणिनः सप्त सप्तधा। यज्ञेषूपाकृतं विश्वं प्राहुरुत्तमसंज्ञितम्॥