Derbyshire Police says the deaths of two horses in a field in Ilkeston appear to be suspicious.
Officers were called to a field off Quarry Hill Road on Sunday afternoon after the bodies of the animals were found by a member of the public.
The horses’ owner was contacted and they were removed from the field.
Post mortem examinations will be carried out but the police believe their deaths to be suspicious.
Officers are appealing for witnesses and are urging horse owners in the area to be vigilant.
Anyone with information is urged to call Derbyshire Constabulary on 101 or Crimestoppers on 0800 555 111.