Today's true sports drinks are still the classic Gatorade -- packed with the electrolytes potassium, magnesium, calcium, and sodium to provide energy during intense workouts -- as well as competitors such as Cytomax, Allsport, and Accelerade.
Performing one or several stretches which elongate the muscles in the affected area should help to provide quick relief. Stand up straight, and then get into a lunging position, with your back leg being the one experiencing the charley horse. Straighten out your back leg while keeping your front leg bent.
There is no answer as to why Rosie developed canker. Because the disease involves a very strict anaerobic process, and seems to have multi-factorial pathogenesis, the true cause of canker is unknown. It is widely thought of as an external infection but horses with systemic or constitutional upset are more susceptible.