Provided herein are methods for treating an animal using a composition that includes active IGF. The methods include treating an animal at risk of having an infection caused by an infectious agent, treating an animal having an infection, and treating a symptom associated with an infection. In one embodiment, the infectious agent is a virus. In one embodiment, the administering includes daily administration of at least 0.05 nanograms of active IGF-1 per kilogram bodyweight of the animal daily (ng/kg), at least 0.1 ng/kg, at least 2 ng/kg, at least 5 ng/kg, or at least 10 ng/kg.
