To see or slaughter an animal in your dream signifies a loss or an end to an aspect of yourself. Consider the significance of the animal being slaughtered. If you dream that a lamb is being slaughtered, then it represents a loss of innocence. If a pig is being slaughtered, then it signifies an end to your greedy or lazy nature.
Dreaming that dogs are being slaughtered or disemboweled represent a bitter ending to a friendship. It indicates betrayal and/or misplaced trust.