Pharmasin is primarily used to control various bacterial infections in poultry, particularly those caused by Mycoplasma species, which can lead to significant economic losses in poultry production. Mycoplasma infections often manifest as respiratory diseases, resulting in symptoms such as coughing, lethargy, and reduced feed conversion rates. By administering Pharmasin, poultry producers can effectively manage these infections, ensuring that their flocks remain healthy and productive.