prsadhrah tu-among them, Prsadhra; manoh-of Manu; putrah-the son; go-palah-herding cows; guruna-by the order of his spiritual master; krtah-having been engaged; palayam asa-he protected; gah-cows; yattah-so engaged; ratryam-at night; virasana-vratah-taking the vow of virasana, standing with a sword.