It can cause muscle damage at the site, even in cows. Since it is supposed to be given intramuscularly, it would need to be given in the breast muscle 1/4 inch deep where it is safest. Not many are comfortable given injections properly, so I usually tell people to give it orally. A couple of years ago, most people could buy Tylan Soluble Powder at feed stores, and use that orally. So, it is just easier and safer.
I have given it to one hen both ways, and haven’t seen any problems. I am not a big antibiotic user or advocate, but when people ask what to use, I usually tell them what will treat a certain disease. People should only use an antibiotic if they know what they are treating, and if they don’t use the right one, they are creating antibiotic resistance.