I winter my bulls out with the cows after preg checking. During the coldest part of the winter they have brush to get in plus straw that I throw out for them to either eat or bed in.
The bulls ranged in age from 3 yearlings that I raised, 3 two year olds, 5 three year olds and the rest being older. My vet mentioned maybe retesting them but didn't seem to think the results would change much. Guess its just one of those years.