Apex domains cannot have CNAME records.
Question and response
Question
dig mcdns.com.br. NS
Answer
mcdns.com.br. 5 NS pns34.cloudns.net.
mcdns.com.br. 5 NS pns33.cloudns.net.
mcdns.com.br. 5 NS pns31.cloudns.net.
mcdns.com.br. 5 NS pns32.cloudns.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0