ययुर्भगवताहूता द्रुतं प्रीत्या स्नुतस्तना: ॥ २६ ॥
drutaṁ prītyā snuta-stanāḥ
The cows had to move slowly because of their weighty milk bags, but they quickly ran to the Supreme Personality of Godhead as soon as He called them, their affection for Him causing their udders to become wet.
Śrīla Prabhupāda comments, “The cows, being fed by new grasses, became very healthy, and their milk bags were all very full. When Lord Kṛṣṇa called them by name, they immediately came to Him out of affection, and in their joyful condition the milk flowed from their bags.”