Secondary zones are not authoritative for a zone and are a read only copy. Secondary DNS zones depend on transferring the data for the zone from another DNS server.
Powershell cmdlet to create a secondary zone is
Add-DnsServerSecondaryZone -Name “western.contoso.com” -ZoneFile “western.contoso.com.dns” -MasterServers 172.23.90.124
Once the secondary zone has been created but the DNS Manager show Zone not loaded, then Zone Transfer needs to be setup on the Primary Zone.
To do this, on the primary zone right click on the Zone and click properties and then select the Zone Transfer tab and add the IP address of the server hosting the secondary zone to allow Zone transfer.