Immune system boosts

[Chickenfever16]

can anyone advise me on what they've found is the best way to boost the birds immune systems ? I tried ACV in their water and they decreased their intake!
Best advice to keep my free rangers healthy. Thanks

 

[Kiki]

Probiotics.

Fermenting their feed.
and
Vitamins.

 

[17 chickens]

Herbs in the water helps