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I'm not going to "jump all over you". I am going to explain why this theory does not work biologically lest people are reading and thinking "Gee! We can keep sickly birds because they'll pass on RESISTANCE!"
Ummmmmm, no.
That would be great if that's how it worked, I suppose. It'd certainly be a whole lot more feel-good for those who like to save everything, if nothing else. Unfortunately, it just does not.
The first thing we have to understand to know why not is how exactly being sick results in immunity or "resistance" to that illness. When a chicken -- or any animal -- is ill the body creates certain antibodies to fight that disease off. In some cases these antibodies remain in the body for a long time after the illness has passed, ready and waiting, to attack should that particular nasty rear its head again. In other cases the body simply "remembers" how to quickly and efficiently manufacture these antibodies; it "learns" how to fight off the disease so next time it's faced with the disease it's able to fend it off quickly and easily. This is an exposure related resistance. It's resistance, but it's not a natural lack of sensitivity such as the resistance that you'll often hear people talking about breeding in.
There are a couple of reasons for this. The first and foremost is that exposure resistance cannot be passed on from chicken to chicken to chicken. It is due to personal exposure and that is the only way it can be gained. Each chicken must develop this immunity on its own. There is evidence that antibodies can be passed trans-ovarially, that is from hen to chick via the yolk in the egg, but these antibodies -- like the antibodies passed to other species in the same way -- are short lived. Most are completely gone by three weeks of life at which point the chick then has zero immunity to those diseases. Another important thing to know with this is that even when antibodies are passed on they're usually passed on in much smaller quantities than they are found in the hen herself which means the chick isn't even wholly protected on day one. He simply has a small amount of antibodies present that may or may not afford him a little bit of immunity. It's also important to know that not all antibodies are passed on to begin with. Antibodies against Salmonella, Infectious Bronchitis, Fowl Plague and a few others have been observed but there have been plenty of trials where none at all were observed as well.
The second is that exposure resistance is expensive. To have every chicken needing to get ill and then better again in order to capitalize on "resistance" is not an economic way to raise birds. In many cases carriers are the exception to the rule, the survivors and the mortality rate of the disease may be as high as 80-90%. Losses are expensive, treatments are expensive, ill chickens are time consuming. Aiming to create birds that will result in time and money down the drain is not effective. That's why we have vaccines, to artificially give exposure immunity to chickens who cannot be reasonably expected to have natural resistance. It's cheaper, quicker and more effective to administer faux exposure immunity than to wait for the real exposure immunity to take its course with one's birds.
Now, the type of resistance you would want to (and can) breed for is natural resistance; a genetic propensity to lack sensitivity to pathogens and a strong immune system to fend them off without clinical affliction. These are the chickens who never fall ill to begin with. Some call them hardy, some call it vigor. Whatever you call it they have a demonstrated ability to not just survive, but thrive. This is "survival of the fittest" because chances are your chicken with exposure immunity wouldn't have survived the disease without your intervention. These are the chickens that can pass their genetics on to offspring and be reasonably expected to create more of the same. Because their resistance is genetic, not created out of previous illness, it can be passed on to future generations.
This isn't to completely discount environment. There is strong evidence across species boundaries that indicates that an overly-sterilized environment leads to a compromised immune system. But there is also strong evidence that a genetic component for reacting in such a way that the immune system is boosted when exposed to pathogens, rather than afflicted with illness, plays a large role in the overall hardiness of an animal -- which includes humans.
lol This is the same thing I said you just used alot more words.
I never referred to building resistance by keeping sickly birds who dont recover. But breeding birds that do recover and ones that dont get sick at all. Your "natural resistance " paragragh. Old timers didnt cull their entire flocks. If they found them they culled the ones that were poorly and not up to snuff. Probably ate em. The survivors that never got ill or recovered were the ones producing the next hatch. Why do I say "found"? Cause on those farms the chickens free ranged everywere. If they got sick they either recover or died in the bushes.
But now when people talk about diseases they refer to culling their entire flock.
Again, is this doing chickendom any favors? Not only having these diseases spread by wild birds but more and more folks are getting chickens.
Having a closed flock will be next to impossible unless you are a chicken farmer with huge sheds to lock them in.
As you pointed out, we are the offspring of survivors. Our chickens should continuie to be the offspring of survivors.
I also am a supporter of vaccines. One of the more natural ways we can jump start the immune system against cocci and mareks.
AGAIN, this is JUST MY HUMBLE OPINION which I am entitled too and do not jump on me for it.
I'm sorry. I don't think I articulated myself very well. We are absolutely not saying the same thing I am specifically responding to the implication that not culling chickens who have survived disease will somehow lead to resistance in the greater chicken population.
This part:
I am not sure that culling a chicken that has survived a disease is doing Ckickendom any favors. In other words- How can we produce chickens resistance to these diseases if we cull them?
And then this in the newer response:
But breeding birds that do recover and ones that dont get sick at all. Your "natural resistance " paragragh.
Birds that recover from disease do not have natural resistance; they have exposure resistance. As I explained above there is a big difference. The very fact that they fell ill to begin with -- thus having to recover -- demonstrates that they do not possess natural resistance. As I explained above, exposure resistance cannot be bred into future generations. The theory simply doesn't translate into reality. It does not work that way. It does work that way for chickens that never fall ill despite exposure to pathogens that would make illness likely. We ARE talking the same thing there, I think.
And, just for clarity's sake, when I say "sickly" I don't mean birds who are consistently or repeatedly ill, but simply those who are susceptible to illness. Probably not the best terminology on my part, best I could think of at the time though.
As to the old timers argument, it's the same as what I responded earlier to the other poster -- sorry, drawing a blank on the name right now -- yes, it's true that old timers didn't cull entire flocks and it's true that some of the best flock management goes back to these days but as I said before the danger comes when you blindly combine modern convenience and technology with old time theory. Old Timers didn't cull entire flocks, but they also didn't coddle sick chickens. How many times in this thread alone have we talked about someone who has an ill chicken in the house or in an "ICU" of some sort? Often with added heat, modern medicines being employed, special diets being offered, etc. We've even had people hand and force feeding chickens to keep them alive. Many times these chickens recover, it's a marvel of our modern times and it's great that people don't have to lose beloved pets, but it renders the flock management of our ancestors absolutely irrelevant.
So yes, if you want to leave your chickens to their devices if they fall ill, offer absolutely no extra supportive care or treatment and then breed the survivors of illness for the sake of capitalizing on the hardiness in recoverability we could certainly make a fair argument that that is doing something for "chickendom"; breeding chickens who survive illness with the incredible amounts of supportive care afforded them by our modern times however, is not in any way contributing to greater resistance or hardiness in subsequent generations.
You are absolutely entitled to your opinion and as I said before I am not trying to jump all over you, but some of what you're proposing just plain doesn't work biologically. It's definitely not personal, I just think it'd be wrong not to respond with the other side of things especially with how many people read and take most of their education from here -- many without ever even responding to ask questions themselves.