DENAGARD (for swine dysentary) works for treating symptomatic birds ! Plus, there is no crossover into the eggs. I discovered it after a lot of searching and over a year of hand feeding one hen that just couldn't overcome the symptoms and giving oxytetracycline daily - it kept the symptoms at bay, but had to be given daily. (I got an infected hen 2 years ago , 2-4 days later 1/2 the flock was sick and ultimately, the original and 4 others died. I treated all and symptoms improved but I know they are all carriers and can't bring in new birds) Since Dec (2017) I have given 1/2 cc Denagard mixed in food, for my approx 5 lb. hen for 5 days and only repeat when symptoms show - about every 1.5 months. She was so weakened and had been separated from the others because they picked on her and pushed her off food and she quit eating. Now, finally, she is eating on her own and my stress level is so much better after 1.5 years of special hand feeding her daily ! Tho' I still keep her separated, she can somewhat integrate when I let them out to free range. What a relief ! Incidentally, I also read that MG is worse in the cold weather (true to experience) and I have manage to get her through 2 winters. The entire area can be disinfected, tho' all my hens area now carriers, and organism will die off in hot dry weather, but is also carried by wild birds, so basically, I'm stuck with it until all my birds are gone and I start over.