Ninety-nine percent of dairy bulls can be traced back to one of two bulls, both born in the 1960s. This means among all the male Holsteins in the country, there are just two Y chromosomes. The females are not much more genetically diverse, shares Chad Dechow, PhD, who cited the inherent risks of long-term genetic homogeneity.
Source: The Bullvine, February 8, 2021. Link.
INSIGHTS: Chasing 200 pounds of milk per day per cow has been valuable, but at what cost if genetic diversity is not successfully reintroduced.