Apex domains cannot have CNAME records.
Question and response
Question
dig univ.com.br. NS
Answer
univ.com.br. 3 NS dns2.univ.com.br.
univ.com.br. 3 NS dns1.univ.com.br.
univ.com.br. 3 NS dns3.univ.com.br.
Authority
The response has no authority records.
Additional
dns1.univ.com.br. 3 A 200.150.224.35
dns2.univ.com.br. 3 A 200.150.224.36
dns3.univ.com.br. 3 A 200.143.131.10
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0