The key to this answer is to highlight that the cure was not medical but a change in lifestyle. Emphasize the role of a controlled diet and physical activity in Tricki's recovery.
The doctor, Mr. Herriot, cured Tricki not with medication but with a practical approach. He took Tricki to his surgery and put him on a strict diet, giving him no food for the first two days and only plenty of water. He then gradually increased his food and ensured Tricki got enough physical exercise by playing with the other dogs. This common-sense treatment cured Tricki of his illness caused by overindulgence.