Śatapatha Brāhmaṇa ("of a hundred paths") 13.3.2.3

13.3.2.3

tadāhuḥ naite sarve paśavo yadajāvayaścāraṇyāścaite vai sarve paśavo yadgavyā iti gavyā uttame'hannālabhata ete vai sarve paśavo yadgavyāḥ sarvāneva paśūnālabhate vaiśvadevā bhavanti vaiśvadevo vā aśvo'śvasyaiva sarvatvāya bahurūpā bhavanti tasmādbahurūpāḥ paśavo nānārūpā bhavanti tasmānnānārūpāḥ paśavaḥ

As to this they say, 'These--to wit, goats and sheep and the wild (beasts)--are not all animals; but those--to wit, the bovine (victims)--are indeed all animals.' On the last day he immolates bovine (victims), for they--to wit, bovine (victims)--are all animals: he thus immolates all animals. They are sacred to the All-gods, for the completeness of the horse, for the horse is sacred to the All-gods. They are many-formed (or, many-coloured), whence animals are many-formed; and they are of distinct forms (or colours), whence animals are of distinct forms.