Chickens pandemia on our wild chicken project. Prevention?

Hola!

So, we have been chicken owners for a year now. We started with a mixed flock of Plymouth Rock and Ameraucanas. A couple of them passed away during the intense heat wave, cause they escaped and couldnt find the way in. But it was an accident, despite that they had a normal life.

Then, I started to think on making this wild chicken landrace project, giving them some food but letting them mostly free range, and started to add different breed. So there was this local place where they had lots of chickens, maybe not the best place to buy, but the 6 years old wanted "the white chickens" so we got three Sussex. One died just two days later, and then life went on... for a while.

Two month ago, one of the Sussex started to act weird, losing mobility, and died. Then, the rooster that we had. And the other Sussex started to behave weird, but then improved and I thought, ok, that's it, whatever we had, it has passed.

So on February 25 I thought "okay, lets continue with the landrace", and I got 2 more Sussex, 3 Blue Andalusians, 2 Brown Andalusians, 7 Leghorns, 3 White Silkies, 4 Brown Silkies, 2 Faverolles, 2 Pekin. I separated them on the free range area for some days, giving them food as I thought they were used to be fed , and then I mixed them with the others. There were no battles as they were seeing each other, so I thought "great!"

And then, last saturday, the surviving Sussex from the first round suddenly died.  Sunday, two silkies ,Monday, two leghorns out. Wednesday, Blue Andalusian out. Today, one Faverolles out. So I lost in one week 7 chickens.

This made me think in the process. I have seen that when chickens are sick and you notice it, it starts to be late. I gave them electrolites, separate them, whatever, but nothing. Well, other Andalusian and other Leghorn, giving them scrambled eggs and electrolites they improved. But the others, one day are running around, next day are looking sick, next day out.

I have to change focus. I am selecting for the best and most adapted, and I am sure some of the breeds are not the best for free ranging, but it is part of the landrace . But losing seven in seven days, just one after the other... I am starting to be paranoid. Obviously there is something around, and it is going faster than me. I can't be all the time nursing sick chickens, specially if they are falling one by one.

So what I am thinking is, how can I improve prevention? Cleaning coop is one thing that we do weekly, giving them fresh water is daily. We throw food around for them and they free range... so what I was thinking is that maybe I should add suplements to the free range, to give the newbies some push. With this I mean adding vitamins to the water or natural treatments like vinegar or garlic. But maybe some of you have experience with free rangers and supplementation. I read about Takota Coen a lot and his chickens, and obviously I should aim for better genetics and make this guys resistant

Just curious, did you get all your different breeds from different growers?

I am no expert, but I thought it might be wise to quarsntine new arrivals before adding them to the flock.
In my country the recommendation is 4 weeks quarantine before letting new birds join the flock. Since you free range, it is easy, just split the pasture.

So obviously you are looking at a quarantine nightmare if you want to introduce half a dozen breeds from different growers.

Here is a pretty thorough article on quarantine.

https://blog.omlet.co.uk/2021/06/21/why-do-new-hens-need-to-be-quarantined/

It would be nice to know what is causing them to die.
I suppose if you brought them in to get autopsied and it was bird flu they would take all your birds,.... at least.

 I heard elderberries help with chicken immune systems.
Maybe some colloidal silver in their water.