Text and illustrations: Brian Crooker (crook001@umn.edu)

The University of Minnesota (UMN), US has maintained a unique herd of unselected Holsteins since the mid-1960s when Dr. Charles Young developed a breeding program as part of a multistate, north central regional (NC-2) project (Young, 1977; Weber et al., 2007). The original foundation cows in the UMN breeding program were paired by genetic merit and assigned to either a low- or high-merit line. The high-merit cows and their female descendants have been inseminated with semen from high Predicted Transmitting Abilities (PTA)-milk sires and represent contemporary Holsteins. The low-merit cows and their female descendants have been bred with semen from sires that were breed average for PTA-milk in 1964 and thus represent average US Holsteins from the mid-1960s. Average milk yield of the unselected Holsteins has remained relatively stable at about 6,500 kg/305 lactation while yield of their contemporary Holstein herdmates has continued to increase.