Domestic livestock and poultry have always been a major source of animal protein, with the sole point in raising them being to fill our bellies. New, improved varieties with rapid growth, greater fecundity or better taste have won favor over time, and pure native strains that haven't been interbred have gradually declined in popularity or even face extinction.
家畜禽一直是人類動物蛋白的主要來源，人類飼養畜禽的唯一目的是「裹腹」，因此在追求商業效益原則下，經雜交改良的新品種，成為生長效率較高、繁殖能力較強的「優等生」，日漸得寵，廣受歡迎。