Feral animals compete for food with domestic livestock. They may damage fences, water sources, and vegetation (by overgrazing or introducing seeds of invasive plants). Though hotly disputed, some cite as an example the competition between feral horses and cattle in the western United States. Another example is of goats competing with cattle in Australia, or goats that damage trees and vegetation in environmentally-stressed regions of Africa. Accidental crossbreeding by feral animals may result in harm to breeding programs of pedigreed animals. Their presence may also excite domestic animals and push them to escape. Feral populations can also pass on diseases to domestic herds.