Did you see my post about asking at Tractor Supply for amoxycillin?
A bacterial infection can occur at any time for any reason. Often some stress or exposure to higher than normal bacteria in the environment can overwhelm a weak immune system. I've had hens get sick with a bacterial infection seemingly out of the blue. Regardless, I start treatment with an antibiotic as soon as I determine a chicken is sick. Some infections can kill in as little as 24 hours, and waiting another day to be certain could end with the chicken dying. I will always choose to assume it's an infection and run the risk of being wrong. An antibiotic won't kill if it's not infection.
A bacterial infection can occur at any time for any reason. Often some stress or exposure to higher than normal bacteria in the environment can overwhelm a weak immune system. I've had hens get sick with a bacterial infection seemingly out of the blue. Regardless, I start treatment with an antibiotic as soon as I determine a chicken is sick. Some infections can kill in as little as 24 hours, and waiting another day to be certain could end with the chicken dying. I will always choose to assume it's an infection and run the risk of being wrong. An antibiotic won't kill if it's not infection.