Pba, the rov tells you the status of the cow. Assuming rov cows (ie more than half) are kosher, each individual cow’s milk is kosher and doesn’t require any bitul
If less than rov cows are kosher then each individual cow is assumed treifa unless you check.
The gemara says rov cows are kosher, some poskim feel thus metzius has changed and currently rov cows are treifa.
In other words if 14% have this problem, each cow is assumed to be from 86% non stapled and all milk is fine. However if 51% are stapled we MAY have a problem