My vet advises 3 hours max for fasting a ferret with possible insulinoma.
The fasting is harder on them because of their already low blood glucose
levels.  If your ferret is sleeping before you take away his food, he may
be fasting longer anyway.  If you start 3 hours before the appointment,
then it will still be under 4 hours even if the vet is running late.  The
secretary probably just gave you their standard cat and dog answer.
 
Blessings
Judith
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[Posted in FML issue 3780]