Hematochezia (bright red blood in or on the feces) can result from a number of different things that generally cause inflammation or irritation of the rectum or anus. It can also occur with diseases of the colon. Causes include:
Rectal or Anal strictures
Problems with the Anal Glands
Perianal Fistulas
Cancers
Rectal Polyps
Inflammatory Bowel Disease (IBD)
Parasites
Prostatic disease (Males)
Constipation
Ingestion of Foreign Bodies (Bones, hair, toys, etc...)
There are also many dogs who will have a few BMs with blood in it from a little bit of stress, and then will not repeat this. The vet will often treat these dogs with a drug called Flagyl, and prescribe a bland diet (boiled white rice and boiled white meat chicken breast mixed in a 3 to 1 ratio) for about a week. If your dog is not on a monthly heartworm preventative, parasites can certainly be a possibility as well.
Based on the history your dog has had for the past couple of days with traveling and eating some food that he wasn't used to...this bout of blood in the stool is most likely just the result of stress. You should feed him the bland diet that I mentioned above for a couple of days and see how he does. If this blood goes away, then you can gradually mix his regular food back in with the bland diet over the course of about a week until you have him back completely on his regular food.
If the blood continues for more than another 24 hours, or he begins to show signs of vomiting or lethargy, then he should be taken to the vet for a check-up. You should also bring a stool sample with your at that time so that it can be analyzed for parasites.
I hope that this information is of help to you, and I wish you the best of luck with your dog. Please let me know if I can be of further assistance.
Dr. K
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