I'm so far behind I have been skimming... This post struck a cord for me. Sorry to hear of your dog's ills. My English Setter, Mose, is also about 13. He was a superb upland dog... the regional director of Ruffed Grouse Society trained him. Due to a move driven by a job change by his wife he had to thin out his kennel. He gave me Mose... steady on the point, steady to the gun, and he set me up for many successful shots on pheasant, grouse, quail and woodcock.
I spent an hour and a half sitting in the outdoor dog run last night as Mose is suffering with congestive heart failure also. He could barely breathe and couldn't stand. I bundled him up and comforted him. The look in his eyes was like he was having a panic attack.... It was nearly 11 PM when he was calmed down, breathing pretty well, and regained his feet. We went back into the house. I was prepared to find him deceased this morning... To my relief he was actually pretty good this morning and this evening.
He has light liver spots and the mud kind of overwhelms them in this photo from October 1, 2017... opening day for pheasant. The past few seasons he didn't get much field time as he was deteriorating with age. He'll get none this year.
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