What does it really mean to 'cull' animals?

Culling means sorting a group of animals into those that are kept and those that are removed, according to traits someone wants or doesn't want. For livestock and wildlife, the removed animals are often killed, because of their sex or species, to keep a population's size in check, or to stop a disease from spreading. The word comes from the Latin colligere, 'to gather', a sorting that is repeated until the remaining group is the size and quality desired.

Culling takes very different forms depending on the setting. Responsible pedigree cat breeders cull by spaying or neutering a kitten that doesn't meet the breed standard, not by killing it; dairy farmers cull 'inferior' cows by inseminating them with beef-breed semen and selling the calves for meat instead of breeding from them. The egg industry culls far more bluntly: since roughly half of all chicks hatched from egg-laying hens are male, and males can't lay eggs, the majority of male chicks are killed shortly after hatching. Culling is also used against diseases that can devastate farms, including foot-and-mouth disease, avian flu, and mad cow disease, where the stated aim is to reduce the spread of the disease.

Out in the wild, culling usually means managing population size directly. In the United States, hunting seasons and licenses are adjusted year to year, allowing more hunting of females when a population has a surplus or restricting hunting entirely when numbers run low; ranchers sometimes invite hunters onto their land specifically to thin elk herds that are eating through winter cattle feed. Culling for population control is common on African game farms and in Australian national parks; with elephants, adults are often targeted and their orphaned young relocated to other reserves. The practice is controversial in many African countries, but South Africa's Kruger National Park banned culling in 1995, and its elephant population has swelled ever since, leading some experts to recommend bringing the practice back.

Culling isn't just about numbers, either. Because it's such a strong selection force, culling based on one trait, like size, can permanently shift a species' genetics. Culling can even be used deliberately to push back against trophy hunting, which favors unfavorable traits because hunters strongly prefer animals with features like the largest antlers; culling 'lower-quality' individuals instead can help counteract that unintended effect. Not everyone accepts any of this: animal rights activists argue that killing animals for any reason, hunting included, is cruel and unethical.