Jaiminīya (Talavakāra) Brāhmaṇa 29.174

This is indeed a stepping across.
"Forward, the swans, eager to drink, toward the sound..."—
the swans eager to drink are indeed the Brahmins.
"From home, the troops of bulls have gone to their abode..."—
the six-day rite is 'from home'; the Chandomas are the 'abode';
the meters are the 'troops of bulls.'
It is the meters that they thus lead forward over to the Chandomas in order to cross over to the subsequent three-day period.
"Friends proclaim together the singing Pavamāna, the irresistibly sound..."—
it is the Bṛhat and Rathantara [sāmans] that are thus harnessed at the morning pressing;
being harnessed, they ascend to the midday pressing.
"He yokes the speed of the wide-striding one; playfully frolicking, the cows bellow..."—
[verses] containing 'cow' and cattle are used, for securing cattle;
for the Chandomas are cattle.
"The sharp-horned one creates abundance..."—
when he says, "abundance": food is abundance, indeed for securing food.
"By day the golden-hued was seen, by night the swift..."—
thus the Atirātra is performed in form.

These are Triṣṭubh [verses] with the characteristic of Gāyatrī, perfected in the form of the day.
Where they perfect the days by form, there success is attained;
success is attained for him who knows thus.
Concerning this they say: "The seventh day belongs to Gāyatrī, the eighth to Triṣṭubh, the ninth to Jagatī. Then why do they begin this Gāyatrī day with Triṣṭubh verses?"
He should reply: "Because all these Chandomas have Triṣṭubh verses as opening strophes."
"Forward, sounding like chariots..."—
these are [verses] containing 'forward' (pra);
it is the form of the introductory rite that they approach thus;
for this day is introductory.
The Chandomas are cattle, for the securing of cattle;
and moreover, cattle are abundance.