(idiomatic) used as a mild oath, or as an expression of astonishment
"Why, dog my cats, they must a ben a house-full o' niggers in there every night for four weeks to a done all that work, Sister Phelps." — Mark Twain, — Adventures of Huckleberry Finn", 1884
I began to feel sorry for Hubby, dog my cats if I didn't." — O. Henry, "The Four Million," 1906
And standing on one leg beside the bath, like Slingsby, had whispered: "Ho, ho, ho! Dog my cats!" mysteriously, to bring luck. — John Galsworthy, The Forsyte Saga, "Awakening", 1920
Buffalo Bill Cody: Dog my cats " - to Annie Oakley, "Annie Oakley"', 1935