The method used to kill 20 sheep near Oamaru yesterday was similar that used in the earlier killing of 195 sheep in the area, police say.
It appeared both groups of animals were shot, initial investigations indicated.
However, it was not yet known what type of firearm was used, Detective Warren Duncan said.
A scene examination was conducted at the Ngapara property today.
Mr Duncan warned farmers to keep a close eye on their stock and be alert to suspicious vehicles or people in the area.
"We're still conducting a large number of inquiries in relation to these incidents but are always very keen to hear from anyone who might have information that could help us."
Anyone with information on either case is asked to contact Mr Duncan on 03 433 1416.