От хозяйского глаза скотина жиреет

you supervise the work yourself you will get best results. See Где хозяин ходит, там земля родит (Г), Свой глаз - алмаз (C)

Cf: The eye of the master fattens his herd (Am.). The eye of the master will do more work than both his hands (Am., Br.). If the owner keeps his eye on the horse, it will fatten (Am.). The master's eye makes the horse fat (Am., Br.). No eye like the eye of the master (Br.). No eye like the master's eye (Am.). One eye of the master sees more than ten of the servants (Br.)