Nowadays it seems that no matter what ails your horse they are prescribed antibiotics. It is common practice not only for horses, but small animals as well. The problem with this is that antibiotics are just what the name implies; against life. The medication does not save the good and get rid of the bad, it gets rid of it all and at the same time compromises the immune system.
Antibiotics work on bacteria, not viruses yet they are prescribed for viruses under the assumption that it is a preventive measure should it become worse. Yet that is contradictory because the damage that is done to the intestinal flora actually sets the stage for bacterial infections. This strategy is destructive instead of productive. Over use of antibiotics causes yeast and fungal infections making horses more prone to an array of hoof infections and respiratory infections. The cycle of re-infection repeats itself due to the compromised immune system and until the proper balance of microflora is re-established.
When the intestinal flora is disturbed by antibiotics, a horse can colic, have diarrhea, go off feed, develop ulcers, have front feet lameness, hives, breathing difficulties, laminitis, and founder in more severe cases. These symptoms do not always show up on the first dose of antibiotics. In many cases, it is after the antibiotics have stopped that the unexplained lameness in the feet show up. The problem eventually clears up and the horse owner never understands why this happened. I have seen this happen not only with antibiotics but with wormers. Anything that throws off the intestinal flora can trigger this type of response. If your horse's immune system is already stressed, chances are they will experience some side effect to this type of treatment.
Unless it is life threatening, there are other options to treating infections of a bacterial nature. The first and foremost is to support the immune system by using herbal remedies. This allows the body to do it's job more effectively. Healing is a part of the natural processes of the body and it does this on a regular basis. When we interfere with this process is when problems occur.
I have never used antibiotics or bute on any horses in over 30 years. I prefer to support the body by honoring the healing process.