What Causes Weight Loss and Loose Stools in Older Dogs?
My dog (approximately 12 years old) keeps having
bouts of diarrhea. This has gone on (off and on)
for about two years. My vet has given him several
rounds of medicine (one for tummy upset and one
for loose stools). Additionally, he has given him
some powder to try to balance the “flora” in his
digestive tract. Also, he recommended I feed him
Purina EN (dry and canned) to help with his
stomach. Nothing seems to help. He likes to eat
grass, which seems to be the only thing he gets
into when he is out in the yard. We give him
Meaty bone biscuit treats. I generally mix in
rice with his food when his stools are very runny.
And now he is starting to lose weight.
Liz
Margate, South Florida
I am a bit troubled by your final comment–that your dog is starting to lose weight.
A number of syndromes can cause intermittent diarrhea, and some animals have irregular bowel movements throughout their lives. For instance, a syndrome called infiltrative (or inflammatory) bowel disease (also known as IBD) is a common cause of chronic, intermittent diarrhea. This disease is frustrating, but treatable.
However, when an older dog develops diarrhea in combination with weight loss, something more serious may be going on. For instance, disorders of the liver, pancreas, kidneys, and intestines can cause this combination of symptoms.
It sounds like your vet has treated your pet for some causes of chronic intermittent diarrhea with special diets and dietary flora supplements. But you don’t mention whether he has run any tests to determine what is causing the problem.
For your dog, I would recommend stool, blood, and urine tests. This combination may lead to an answer. If not, you may need to follow up with X-rays and ultrasound.
Unless you know what is causing the problem, you will face an uphill battle to eliminate your pet’s symptoms.
You have questions. 
omg.. good work, guy