Calving difficulties are rare. Generally, it's better, from a safety standpoint, to not disturb bison cows during calving. A bison cow will live longer and be productive about twice as long a beef cow. Some bison cows have been documented to produce calves for 40 years. In contrast to a beef cow, bison stand facing into the wind and snow.
Bison are very hardy, requiring no shade in the summer or shelter in the winter.
They are very disease resistant. In fact, very few bison producers vaccinate for anything. Parasite control is important. Most producers report they treat with Ivomec one or more times a year. However, many producers do not treat at all.