If he is truly
Kingfamfarm wrote: completely separated from the herd.
then my first question is, Are all of the cows bred? Another would be what ClinchValley asked.
If nothing is wrong with the bull, and the cows are NOT bred, I'd say you need to ship the bull.
If there is something wrong with him, can it be treated, and will he be good to breed in a timely manner to get the cows bred?
I don't want to get you worried, but one of the thoughts that came to my mind is anaplasmosis.
If you are reluctant to, don't be, and make a call to your vet. Chances are, if they have worked on large animals, they can help you.