From Two Bulls, 9 Million Dairy Cows
For answers, the researchers have begun breeding a small batch of new cows, cultivated in part from the preserved semen of long deceased bulls, to measure a host of characteristics — height, weight, milk production, overall health, fertility, and udder health, among other traits — and compare those to the modern Holsteins we’ve created. Long ago, farmers would bring in bulls from other farms to get their cows pregnant — a way of ensuring genetic diversity, or “stirring the pot,” as Hansen says. A complex algorithm analyzes the bull’s genetic makeup, taking into account the health of his offspring, their milk production, the fat and protein in the milk, and other traits, to come up with figures that rank him against other bulls.
Source: undark.org