Russ and Scooter,
>thin and dark stool over the past few weeks
>somtimes its larger then normal and then it issmall and dark
 There are several diseases that can cause this;
1) Dietary indiscretion-- if he is eating somthing that is causing irratation
to his GI tract
2) GI ulcers-- there is usually an underlying bacterial infection.  The
symptoms can include one or more of the following: loose stool, dark stool(it
contains digested blood), poor appetite, weight loss.
3) Eosinophilic gastroenteritis-- this is less common and usually the is not
blood in the stool.  On a blood test the albumin is usually low and
eosinophil (a type of white blood cell) count is up.
4) GI parasites-- this is less common, but giardia and coccidia can cause
this.
5) Lymphsarcoma-- this can present this way and as it progresses will cause
weight loss, poor appetite.  On a blood test the lymphocyte count is usually
high (a type of WBC)
 
As you can see there are many potential causes.  I would recommend you see
your vet and they perform a good physical (and bring them a fecal sample of
at least the abnormal dark stool for a routine micro exam and an occult
blood--a chemical test for blood), and at least a CBC blood test.
 
Good Luck,
Dr Weiss
301-299-4142
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[Posted in FML issue 1118]