Is probios necessary when using nuflor, micotil, baytril or even penicillian? Can't say that I have ever used it on my calves, and I very seldom loose one. I watch them close and try to get them doctored with pen G and sustatian III boluses. I try not to use the higher prowered antibiotics unless I have to. I can usually get them cleared up the Pen G and boluses. At what point and which ones will knock out the normal flora?