Oh man , poor fella! Giardia is bad.
Giardia can be hard to get rid of, so certainly go back for a recheck with your vet.
Have you changed food recently or changed the amount you are giving? Any new treats? Did the vet find giardia in a stool sample?
Please be aware it is contagious to humans too! So it's important to be sure he doesn't get reinfected. It is usually contracted by drinking from puddles or any standing water. Disinfect any surfaces his poo has come into contact with and no drinking from water holes or even eating snow.
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