The application of genetic principles to improving heredity for economically important traits in domestic animals. Examples are improvement of milk production in dairy cattle, meatiness in pigs, growth rate in beef cattle, fleece weight in sheep, and egg production in chickens. Even after thousands of years of domestication, domestic animals respond readily to genetic selection. Selection permits the best parents to leave more offspring in the next generation than do genetically inferior parents. Many specialized breeds and strains have been developed for the production of meat, fiber, and milk that are adapted to different environmental and economic conditions.