कारस्तदस्य पशवोऽन्वायत्तास्तस्मात्ते हिकुर्वन्ति हिंकारभाजिनो ह्येतस्य साम्नः ॥
In plain words
The hiṅkāra is that upon which these cattle depend; therefore they indeed make sounds, as they are sharers in the hiṅkāra of this Sāma.
Close to the Sanskrit
The hiṅkāra—to that are his cattle dependent; therefore they indeed do make, because they are partakers of the hiṅkāra of this Sāma.