In Part Four of this excerpt from the new book Equine ER , Selena, a Bluegrass polo pony who was found critically injured in a field, struggles with a setback after finally leaving the clinic. When she is released from the hospital, Selena appears fully on the mend. But during the polo pony’s rehabilitation, after it is apparent the pain is increasing in her left hind limb, she is diagnosed with laminitis...