I introduced a new hen in to my small backyard flock a week ago. The stress of getting acclimated has given her a breathing issue. I can hear a rumbling when she breathes. I've used Vet RX for 2 days and it hasn't helped. I'm thinking an antibiotic would be a good choice before it gets worse. I have Pen G on hand but read many use Tylan for respiratory problems. Opinions?