Respiratory infections in chickens can be caused by various pathogens, including bacteria, viruses, and mycoplasmas. Common bacterial culprits include *Escherichia coli*, *Pasteurella multocida*, and *Mycoplasma gallisepticum*. These infections can lead to serious conditions such as chronic respiratory disease (CRD) and avian influenza, which not only harm the birds but also threaten the poultry industry economically.