Śatapatha Brāhmaṇa ("of a hundred paths") 13.3.4

Verily, the horse is slaughtered for all the deities: were he to make it one belonging to Pragâpati (exclusively), he would deprive the deities who are co-sharers of their share. Having made ghee (to take the part of) portions (of the horse's body) he makes oblations to the deities in mentioning them one by one with (Vâg. S. XXV, 1-9), 'The Grass (I gratify) with the teeth, the Lotus with the roots of the hair,...:' the deities who are co-sharers he thus supplies with their share. When he has offered the Aranyeऽnûkya (oblations), he offers the last oblation to Heaven and Earth; for all the gods are established in heaven and on earth: it is them he thereby gratifies. Now the gods and the Asuras were contending together.

They (the gods) spake, 'We are the Agnayah Svishtakritah of the horse (sacrifice); let us take out for ourselves a special share: therewith we shall overcome the Asuras.' They took the blood for themselves in order to overcome their rivals; when he offers the blood to the Svishtakrits, it is in order to overcome (his own) rivals; and the spiteful rival of him who knows this is undone by himself.

The first oblation (of blood) he offers in the throat (gullet) of the Gomriga; for Gomrigas are cattle, and the Svishtakrit is Rudra: he thus shields the cattle from Rudra, whence Rudra does not prowl after the cattle where this oblation is offered at the Asvamedha.

The second oblation he offers on a horse-hoof; for the one-hoofed (animals) are cattle, and the Svishtakrit is Rudra: he thus shields the cattle from Rudra, whence Rudra does not prowl after the cattle where this oblation is offered at the Asvamedha.

The third oblation he offers in an iron bowl; for the people (subjects) are of iron, and the Svishtakrit is Rudra: he thus shields the people from Rudra, whence Rudra does not prowl after the cattle where this oblation is offered at the Asvamedha.