Holstein-Friesians 155 



relationship, and the reason is that milk- 

 producing energy is not developed in one sex 

 and later transferred to the other to be used 

 there. Bulls do not develop milk-producing 

 energy, and the bulls in our Holstein-Friesian 

 pedigrees are generally young animals. The 

 reason why the dams of sires in these pedi- 

 grees are older than the dams of dams is 

 simply that the bulls give more opportunity 

 for selection to eliminate young dams. 



