I Have An 11 Yr Old Female Yellow Lab Mix.

I have an 11 yr old female yellow lab mix. The last few days some of her stools are black all the way through the stool and sometimes only around the outside of the stool. She is eating, drinking as normal, has good energy level, plays and walks. I have been giving her 2,000mg of fish oil and a probiotic daily for the last 12-15 months.