link between poultry lice and poultry respiratory disease.
I think I'm seeing a link between poultry lice and respiratory disease in my pastured meat birds. Breeding parents are treated with Ivermectin and are both lice and sniffle free, but chicks in growout pen get both before harvest at 12 weeks. I'm unaware of any studies making the connection. Are there any that you are aware of?
Outside United States poultry
I am unaware of any research that shows a connection between lice and respiratory infection. It is known that insects can carry pathogens; however I dont think that is what is causing/spreading the disease. I suspect that your older birds may be be carrying CRD (mycoplasma) and not showing any symptoms. This is a slow acting disease that takes several weeks for it to express itself in birds.
I would suggest treating your birds for CRD and see if the respiratory issues go away in the younger birds. Or as an alternative you can stop treating your older birds with Ivermectin to see if they catch the respiratory disease.
Good luck and keep us informed if you try and figure it out