I've used it by injection in horses *many* times, and it did not cause any issues with them.@Anabariful be careful of injection site soreness and watch for necrosis... I don't *think* penicillin causes injection site necrosis, but I would talk to Kathy @casportpony about it first... it can be drawn out with a needle and then given orally as well...
I once asked a vet about giving it orally and she said something like "no, injectable penicillin should not be given orally because it's poorly absorbed".
Hens go broody when you don’t want them to… and won’t go broody when you do. 
