Fifteen cows were found dead in mysterious circumstances near a pond in Bajrang Nagar area in Ujjain, following which the Vishva Hindu Parishad (VHP) called a bandh in the district on Monday.
Twelve cows were found dead near the pond on Saturday, and three more were found early this morning, police said.
As news of the death of the cows spread in the city, VHP activists staged a protest outside the Superintendent of Police's office in Ujjain, demanding the arrest of persons they said were behind the incident.
They alleged the cows were killed by a section of a minority community to hurt the religious sentiments of the majority community.
Police said it was suspected that the cows had died after eating some poisonous substance.
VHP's leader Ashok Kotwani announced his organisation has called "Ujjain bandh" on Monday to protest the incident.
The carcasses of the cows were sent for autopsy and no arrests have been made so far in connection with the incident, police said.