When travelling from Latvia to Denmark the following requirements for the pet must be met:
Besides ID the animal must have an EU Pet passport. The passport can be issued by a veterinarian and is only valid, if it is certified that the animal has been vaccinated against rabies. It is important, that the most recent rabies vacciation date is not prior to the date of identification.
Primary rabies vaccination must be given at least 21 days prior to departure.
If the animal already has a rabies vaccination, which is still valid, it is not necessary to redo the vaccination.
For more information please see the link of the Danish Veterinary and Food Administration below.