In contrast, several B. taurus breeds in developed countries have been subject to systematic selection for milk production for a very long time. This selection has been particularly effective in the last fifty years because of the introduction of artificial insemination. This makes it possible to progeny-test males with great accuracy and to greatly extend their reproductive potential. The result of these separate evolutionary histories is that while tropical breeds of cattle typically produce less than 1,000 litres of milk in a lactation, developed dairy breeds such as Holstein, Jersey or Brown Swiss can, if properly managed, produce up to ten times this amount.