Likewise, over the last four decades, improved breeding methods, higher-quality feed, and better veterinary care have more than doubled average milk production worldwide. Nevertheless, regional discrepancies remain massive: cows in the Netherlands can produce roughly 9,000 liters of milk annually, while Zebu cattle in the tropics produce only about 300 liters.
比如，一种新的非洲旱稻——非洲新稻（Nerica）能将年产量翻三倍。类似地，在过去四十年中，改良的喂养模式、高质量饲育和更好的兽医服务让全世界平均牛奶产量增加了一倍多。尽管如此，地区差异仍然巨大：新西兰的奶牛一年可产奶9000升，而热带地区的瘤牛只能产300升。