This article from The Labrador Site takes a look at Giardia in Labradors. What causes it, the symptoms, diagnosis and possible treatment options: Giardia in Labradors.
This is a horrible thing that is not always easy to get rid of. You need to retest a few weeks after treatment - no, I am not a vet, just speaking from experience - and you must be really careful to clean up any toileting in your garden as the spores are terribly good at re-infecting. Thank goodness for health insurance as the testing is expensive.
