Śatapatha Brāhmaṇa ("of a hundred paths") 6.5.2.19

6.5.2.19

tāṃ haike dvistanāṃ kurvanti | atho aṣṭastanāṃ na tathā kuryādye vai goḥ kanīyastanāḥ paśavo ye bhūyastanā anupajīvanīyatarā vā asyaite 'nupajīvanīyatarāṃ haināṃ te kurvate 'tho ha te na gāṃ kurvate śunīṃ vāviṃ vā vaḍabāṃ vā tasmāttathā na kuryāt

Some, indeed, make it with two nipples, or also with eight nipples; but let him not do so, for those cattle which have fewer nipples than a cow, and those which have more nipples, are less fit to yield him a livelihood: hence they make this (fire-pan) less fit to yield a livelihood; and, indeed, they do not make it (like) a cow, but (like) a bitch, or a ewe, or a mare; hence let him not do so.