Sometimes you know it’s time: When an older horse in less-than-ideal health suffers a serious bout of colic, euthanasia might be the best option. Other circumstances tell you it’s not time: When an otherwise healthy horse develops a potentially life-threatening condition, treatment might be the better choice.

But what about when it’s not so clear-cut–when continued medical treatment and careful management are options, but the animal’s quality of life could go downhill very quickly. Do you stay the course? Do you opt for euthanasia?

My horse’s “girlfriend,” Maddie, a 13-year-old Thoroughbred/Paint mare owned by my good friend Emily, had earned the nickname “Mad Cow” because of her sometimes cantankerous temperament. From a distance Maddie looked like a picture of health: well-conformed with a sturdy build, solid bone structure, and good muscle tone. If you took a closer look, though, Maddie had significant health problems.

First, there was recurrent airway obstruction, or heaves. Certain environmental triggers, such as dust mites, would set off a reaction of labored breathing and coughing. She often required clenbuterol, even in open, airy stables. Maddie was also allergic to alfalfa as well as to many other plants. Fortunately, the lush Kentucky pastures she grazed and a specialized feeding program were enough to keep her in good body condition.

But the health issues didn’t stop there. Maddie had developed a rare form of photoactivated vasculitis. Essentially, she was allergic to the sun: If she spent too much time in the sun, she developed painful lesions all over her body. Her condit