Mary those are a variation/mixed breed of pitbulls,
a mixed bag at best, the majority are excellent people dogs, a bad, very bad minority are dangerous to animals, very strong prey drive, there is a good possibility that these were dumped, the 'good' pit bulls are very family and home territory oriented. Roaming is just not a big trait to them.
From long experience the best answer is SSS.
Protecting your livestock has to come first.
The donkeys are really great guardians, and fun, I love them. A livestock guardian dog is excellent too, Pyranees, Akbash, many of them, and they sound the alarm, and with the Akbash and related stand their ground, one of the few breeds ready to take on a roaming pit bull. And they are excellent with kids and granduns.