Going to apologize in advance for this long post! Both us and the vet are completely flustered with my dog's condition.
I have a four year old Border Collie that has always been incredibly healthy. Active, lean, well trained, happy dog. She was on a Nutro High Energy diet for years with no problems and did great. When we moved to a new state, we could not find her food anywhere without special ordering so we switched to a higher quality food with a similar Protein/Fat/Fiber/etc ratios. She does not chew/destroy things or eat anything she's not supposed to with the exception of stealing a few grains of horse feed on occasion (that horses drop while eating).
After the switch (a very, very gradual intro to the new food), we noticed she started having intermittent diarrhea. Knowing it can take a dog up to 8 weeks at times (according to our vet) to fully adjust to their new diet, we just kept a close eye on her. After four or five weeks, we started noticing blood in her stools and that's when we went straight to the vet.
They have since taken a fecal twice, and both times they came back clean. So no parasites. No Giardia. All her vitals are normal, no fever, and she's not had ANY other symptoms. No vomitting, lethargy, abdominal pain, or anorexia. She is just as happy and playful and content as ever, with complete control over her bodily functions.
Treatment 1: The vet sent us home with an anti-biotic (Metronidazole), and Sucralfate (an ulcer medication). She was on these for about 6 days, we never missed a dose. On the meds, her stools returned to normal and we were excited, but once the last dose of the antibiotics wore off (after about 12-24 hours), the bloody diarrhea came right back.
Treatment 2: The vet suggested we try a Hypoallergenic food next, saying it may be a food allergy. She merely picked at this new soy-based food for a few days and then refused to eat. After four days without much more than a kibble or two once in a while in her, we took her back to the vet. They ran another fecal, took blood and urine for analysis, and suggested we put her on a lamb & rice diet for sensitive stomachs since she wouldn't eat her HA food ("not worth letting her starve").
The next day I got a call from a frustrated vet who told me every single one of her levels came back "middle of the road normal." From what they could see in the bloodwork/chemistry panel/etc, there was nothing that stood out, nothing to indicate liver or pancreas diseases.
Since on her lamb & rice diet, she has been gobbling her food down with every meal (within 30 seconds to a minute), something she's never done, even as a puppy. So she obviously likes it/has a good appetite.
The vet is flustered at this point. They gave us another dose of antibiotics since they seemed to help, but the bloody diarrhea came back again as soon as the meds wore off. They suggest giving her a few weeks on the new food to see if her gut settles, and say the next step would be to take ultrasounds, and then biopsies from her digestive tract to see if she has cancer or something else not showing up in the bloodwork.
Has anybody else experienced a dog with bloody diarrhea and NO other symptoms? Are biopsies really the only next logical step? A friend of mine suggested taking her for a full-body MRI that a local vet clinic offers. Any ideas what this may show? Would it be a safer way to see if there's cancer?