Śatapatha Brāhmaṇa ("of a hundred paths") 13.3.3.2

13.3.3.2

śakvaryaḥ pṛṣṭham bhavanti anyadanyaccando'nye'nye hi stomāḥ kriyante yacakvaryaḥ pṛṣṭham bhavantyaśvasyaiva sarvatvāya

The Sakvarî verses are the (Hotri's) Prishtha (of the second day): there is a different metre for each (verse), for different Stomas are performed on each (day). And as to the Sakvarî verse being the Prishtha (-stotra), it is for the completeness of the horse (sacrifice).