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Why is my dog's poop light brown with red after heartworm meds?

Updated on September 23rd, 2025

Pet's info: Dog | Mixed Breed | Male | 35 lbs

Gave my dog heart worm medicine yesterday. This morning and now afternoon his stool looked odd. Usually it’s dark brown like the pure balance I give him but today it’s light brown with possible mucus and small red chunks. What could this possibly be and should I be worried?

1 Answer

Most Helpful Answer

Dr. Leigh, DVM

Answered By Dr. Leigh, DVM

Veterinarian

Published on February 19th, 2019

He could have colitis secondary to something he ate. You could feed him a bland diet of chicken breast and white rice for a few days and see if that helps. You could also add a probiotic to his diet, like Fortiflora or Proviable. If the abnormal stools continue then he should be examined by a vet to determine the cause and treat. Your vet can run a fecal test to make sure he doesn't have a parasite.
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