In general, we look for Heritage Breed animals to raise. Heritage breeds are those that have been bred for generations and retain qualities that modern hybrid breeds do not possess. The Livestock Conservatory states that heritage breeds were bred to be self-sufficient and survive using older farming methods. Some of these characteristics are high fertility, foraging ability, longevity, maternal instincts, ability to mate naturally, and resistance to diseases and parasites.
Which breeds are heritage breeds? As a quick reference, they are the breeds of livestock that you would have seen at your great-grandfather's family farm. Unfortunately, many of these breeds are diminishing in numbers as they frequently are not suitable for large commercial farming. Therefore many of them are on the endangered, threatened or recovering species list.