Provided herein are methods for increasing the concentration of insulin-like growth factor (IGF) in the serum of a subject. In one embodiment, the method includes administering active IGF-1 to a subject, wherein the concentration of IGF in the serum of the subject is increased. Also provided are methods for treating a condition in a subject, methods for improving or maintaining the health of a subject, and methods for improving a characteristic of a subject. Examples of conditions include a motor neuron disorder, Alzheimer's disease, myocardial infarction, hypoxic-ischemic brain injury, osteoporosis, skeletal muscle repair, and growth failure. Examples of characteristics include increased milk production, increased fertilization, increased reproduction, increased growth, increased oocyte quality in a ruminant undergoing superovulation, and increased embryo viability. In one embodiment, the IGF-1 administered to the subject is obtained from a natural source that has been processed to increase the amount of active IGF-1.
