I haven’t had a lot of dogs because most of my dogs have gone to a good old age but this means I have had a fair amount of experience of having older dogs.
For a long while I had two working Springer Spaniels, Hebe and Mack, whose ages were exactly ten years, I referred to them as my old dog and my young one. Hebe was fit and active up twenty when I lost him but then I realised my “young dog” was actually ten year old! Mack is now eleven and I am very aware that he needs the right exercise regime for an older dog and a diet tailored to an active working dog.
