my 1 year old female 75 lb doberman, sharpei, Staffordshire terrier mix has been having black stool a few times a week. It's solid in firmness, but pure black. Sometimes mixed in with the brown sections. Ran a preliminary parasite test on a black sample at VCA, was negative. Ran a more comprehensive sample through a lab via my regular vet, which included test for occult blood, all returned negative on a pure black sample. Just got these most recent tests back today, can anybody provide ideas about what might be going on? First suggestions might be to try a different food, she's on Taste of the Wild Salmon, she was on the lamb flavor before. She was on glucosamine chondroitin for hip dysplasia but I took her off that because I believe it increased the frequency of the black occurrence. Also takes fish oil with her meals. Chews knuckle bones, elk antlers, and a Greenie dental chew per day.