Sorry to hear this. Our Irish Setter died last year. The last four months of her life she lost her appetite and lost weight and condition. Towards the end she looked so rough I worried someone would turn us in for neglect, yet she was spunky right up until the last week. The vet said it was just an old dog issue, she had nothing that could be treated. We offered her every thing we could think of those last months to try to get her eating. Sadly, 13 is just a very old age for big dog and we can't turn back the clocks.