Gobhilagrihyasutra 3.6.3

3.6.3

- puṣṭikāmaḥ prathamajātasya vatsasya prāṅ mātuḥ pralehanāj jihvayā lalāṭam ullihya nigired gavāṃ śleṣmā 'sī 'ti.

If he is desirous of thriving (in his cattle), he should lick with his tongue the forehead of the firstborn calf, before it is licked by its mother, and should gulp with (the formula), 'Thou art the phlegm of the cows' (ibid. 3).