ehs.zts.com has no NS records.
NS records for this zone are defined at zts.com.
NS records for this zone are defined at zts.com.
Question and response
Question
dig ehs.zts.com. NS
Answer
The response has no answer records.
Authority
zts.com. 3601 SOA dns1.registrar-servers.com. hostmaster.registrar-servers.com. 1677176732 43200 3600 604800 3601
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0