THIS IS A SCIENTIFIC FACT!
IMPORTANT: all chickens need a PH balance in their coop litter or bedding from AGED compost depending on your type of weather conditions of at least 6.5 to 7.0 or more PH balanced poultry litter - Most commercial litters are neutral 7.0 or below to ACIDIC (pine shavings 5.0 to 6.4) and too acidic of the litter can be bad for your chickens health, You can add high PH hydrated barn lime of 12.0 to your litter to bring up the PH levels
Because all coops are in different climates and regions - no two coops, humidity and situations are ever the same. Chicken owners raise chickens outdoors coops so its important to keep a healthy PH levels, the ammonia levels balanced and wet to dry ratio balance based on your changing weather conditions
So you can see that weather is always changing, so is the health of your coop during different seasons
In some cases, chicken owners think they have "sick" chickens from disease, when the reason is poor unbalanced chicken litter on the floor of the coop.
Chickens that eat bacteria (they ALL do) eat dirt or poop and other germs from the ground can ingest bacteria that remains "dormant." Now when the weather changes outdoors (In Texas we can have 30 to 50 Fahrenheit degree changes in a matter of hours.) Or from dry to wet (or wet to dry!) The "dormant" bacteria that your chicken ate can become "active" and cause illness in chickens.
Most chickens recover and have strong immune systems to absorb bad bacteria and re-align their gut systems.