re: 70 pound black lab may have eaten some rat poison pellets

There's a pretty good chance you got a bit of it out. The vitamin K is a good idea - make sure to give as long as your vet recommends

About once or twice a day just check his gums and eyelids to make sure they're nice and pink. If you see them become pale or develop any red splotches (petechia) in these areas call vet asap.

Also watch his urine and feces to make sure he isn't passing blood in them. The urine will look rust colored. The feces will be very black in color. Sudden onset lethargy, coughing, exercise intolerance also to watch out for. All of these are a problem