I have a three year old male English Setter. When working in the field his endurance is about 1 hour and 15 minutes regardless of the outside air temperature or the amount of "yard work" or "exercise " he receives. We have a large fenced yard that we work him in twicedaily, with emphasis on the hot days so as to bulid his stamina. When we go out to actually hunt, he is typically very enthusiastic but after that magic 1 hour 15 minutes he is "out of gas". His breathing becomes very difficult. He eats grass and then naturally vomits. After which, he gets lethargic and has an extremely difficult time moving air. At time, he seems to have a somewhat blue tongue and if I were a Doctor, I might think he is asthmatic. I have had my vet check him very thoroughly for any type of airway obstruction, to include sedation and scope of his entire breathing system. The vet's recommendation is to administer prednisone prior to hunting and monitor his reaction. We have tried this tactic and see little, if any difference.

Has anyone else expereienced anything like this, or have any ideas whatcould be the problem?