My GSP is 8.5 years old.  We hunt quail with about 20 times per season.  In the last couple of seasons I've noticed that regardless of the outdoor temperature he pants constantly, hence, he is pointing fewer and fewer birds.  He has always been in good health and we exercise him year round. 

If anyone has any suggestions as to what may be his problem and how to correct it, I would really appreciate it.

Thank you!