Twenty lactating primiparous Holstein-Friesian cows 40 days in milk were randomly allotted into four treatment groups that consisted of a wheat-based , pelleted basal diet with no supplemental CDCO ( control ) , basal diet with CDCO added at 25 ml/kgDM ( DM ; dry matter ) ( low ) , 35 ml/kgDM ( medium ) and 50 ml/kgDM ( high ) in an eight-week feeding trial , after two weeks of adjustment .