Perfect Strangers (1986)

S6E4 A Horse is a Horse

Larry and Balki decide to invest in a racehorse, but their excitement turns to disappointment when the horse finishes dead last in its first race. Soon after, they learn that the horse suffers from an incurable illness. Undeterred, Balki brings the horse back to their apartment, believing that a special Myposian potion might be the key to healing him.