Verse 2.6.1

पशुषु पञ्चविधं सामोपासीताजा हिंकारोऽवयः प्रस्तावो गाव उद्गीथोऽश्वाः प्रतिहारः पुरुषो निधनम् ॥ २.६.१ ॥

paśuṣu pañcavidhaṃ sāmopāsītājā hiṃkāro'vayaḥ prastāvo gāva udgītho'śvāḥ pratihāraḥ puruṣo nidhanam || 2.6.1 ||

1. This is how a person can perform the fivefold Sāma worship in animals. Think of goats as hiṃkāra, sheep as the prastāva, cows as the udgītha, horses as the pratihāra, and human beings as the nidhana.

Word-for-word explanation:

Paśuṣu, in animals; pañcavidham sāma upāsīta, one can perform the fivefold Sāma worship; ajāḥ, goats; hiṃkāraḥ, are the syllable hiṃ; avayaḥ prastāvaḥ, sheep are the prastāva; gāvaḥ udgīthaḥ, cows are the udgītha; aśvāḥ pratihāraḥ, horses are the pratihāra; puruṣaḥ nidhanam, a human being is the nidhana.

Commentary:

Goats are the most common of these animals, and they are also the most widely used in sacrifices. This is why they are given the first place as hiṃkāra. Ajā, goats, and avi, sheep, are often seen together, and they are very similar. So also, hiṃkāra and the prastāva are often together. This is why avi, sheep, are said to be the prastāva. Cows are the udgītha because they are superior to other animals, as the udgītha is superior. Then horses ‘carry’ (pratiharaṇa) people, so they are the pratihāra. And as animals ‘depend’ entirely upon human beings, so human beings are their nidhana (here, nidhana means ‘support’).