domain controller and Additional Domain controller not identical

Hello,

i have domain controller and additional domain controller both now working , i have Also exchange 

the computer container & domain controller container  in DC is empty , all computers appear in ADC.

today i am try to search for (Microsoft Exchange System Objects)  did not find it on DC if find it ADC

NOTE: if create user in DC or in ADC it appear in both server.

please Advise me.

thanks