I don't bring in new chickens and just plop them in, but that is just me because of biosecurity reasons. It's not that I know something bad will happen if I do, just that I don't need to risk it, so I don't. Why take unnecessary risks? I get hatching eggs or baby chicks from a reputable hatchery when I add new blood.
There are plenty of people that take chickens to shows and do not quarantine them when they get back. There are plenty of people that go to chicken swaps and such and don't quarantine or isolate.
To put it in terms of a formal risk assessment, what are the odds of something bad happening and, if something bad happens, how bad is it? We each assign our own levels to both sides of that equation. To me, the odds of your chickens getting something that will wipe out your flock are pretty small. It just does not happen that often, but when it does happen, it can be devastating. Some people consider their chickens as pets and almost part of the family. Some have worked a long time on the genetics. Some depend on a large flock for income. Some people would sterilize and start over, not a big deal. So just how devastating your flock getting wiped out would be to you varies with each of us.
The odds of you getting a disease or parasite that will not wipe out your flock but that can be treated are higher. It still does not happen that often and when it does happen, it is not devastating to most of us. Many of us would consider it more of an inconvenience. But some people would really freak out at the thought of their babies getting a parasite and needing treatment.
When I integrate young brooder-raised chicks, I basically just turn them loose with the flock. They have been raised where they can all see each other, and I think that helps, but I also think if you have plenty of space, that does not matter that much. If space is tight, I think it matters a lot more.
The way I look at most of the recommendations on this forum, they are guidelines, not absolute laws of nature. They are intended to cover practically any situation for practically anyone and keep them out of trouble. They are over the top for most of us, but they are intended to keep practically all of us out of trouble, even if we do some things wrong.
An example is the temperatures in a brooder for young chicks. I don't know where your brooder is located, how drafty it is, how many chicks you have in there, anything like that. If you rigidly follow the guidelines, your chicks will survive. But in almost all occasions, they don't really need those temperatures. I have a fairly large brooder and just keep one area warm. The rest cools off way below the recommended temperatures. They spend a lot of time in the cooler areas and do fine. I don't even measure the temperature in the warm area. I just keep one area warm enough and let them choose their comfort zone. But by their nature, some people have to have and follow rigid numbers. And when you are just starting out, it really helps to have numbers to go by.
So what have you done to your flock, in my opinion? From a disease viewpoint, you have put them at risk, but probably not that high a risk, especially for something serious. Definitely watch them pretty closely for the next month, but don't panic. From an integration viewpoint, sometimes it goes so smoothly you don't know what all the worry was about and sometimes chickens die. Usually, and especially if you have some room, there is some pecking, maybe minor fighting, but if you leave them alone, they'll sort it out without any real harm.
but I just got lazy. I plopped 2 new roosters and a hen in, as if they fell from outer space. The new boys are the two tall dark and handsome ones in the back. the hen ducked down because she's shy. The girls like them. I don't blame them.
