What I found is along the same lines, maybe just slightly different depending on which species it's being used in...According to the information I found when asked if bacitracin was harmful to guineas is that Bacitracin as the medication in gamebird feed is put there specifically to combat ulcerative enteritis in quail.

https://www.drugs.com/pro/bmd-soluble.html, where the following quotes came from...
Broiler and replacement chickens
An aid in prevention and control of necrotic enteritis caused by Clostridium perfringens susceptible to bacitracin methylene disalicylate.
Growing turkeys
An aid in control of transmissible enteritis (blue comb, mud fever) in growing turkeys complicated by organisms susceptible to bacitracin methylene disalicylate.