Why did most of the hog owners keep four or five barrows to run with the sows?

Most of the owners kept the old "barrows" to run with the sows to protect them and the shoats born every year. Barrows weren't anymore vicious than boars, but the boars would "generally pulled off to range alone", and the barrows generally stayed with the sows in order to keep the sows and the shoats safe from predators.