A cull is usually indicative of your immune system fighting off a threat of disease. For example, to dream of killing young mutated animals in the wild indicates fighting off cancer in your body – cancer is mutated cells. The animals quite often are shown as young or not fully developed as this is the stage where you want your immune system to spot the threat and deal with it. Note, however, that the animals do not have to be young – once they are shown negatively it means the same thing. Black and white or menacing black animals mean the same thing. Overgrown animals also represent a threat and are good to kill in a dream.