CC Ādi 17.162

jarad-gava hañā yuvā haya āra-vāra
tāte tāra vadha nahe, haya upakāra
Synonyms: 
jarad-gava — old, invalid cows; hañā — becoming; yuvā — young; haya — become; āra-vāra — again; tāte — in that action; tāra — his; vadha — killing; nahe — is not; haya — there is; upakāra — benefit.
Translation: 
“The killing and rejuvenation of such old and invalid cows was not truly killing but an act of great benefit.