There's one answer:
The guy says the vehicla and trailer must conform to the rules that apply in the originating country. The load (the cat) must be marked according to Dutch law.

Dutch law means among other things that you need a 50cmx50cm red/white striped plate, with a light if you are going to be traveling in darkness or diminished sight conditions.

The width would be OK because there is an exception for "indivisible loads", as there is for length (masts). Masts can not stick out more than 5meters behind the rearmost axle of the trailer.

Hope this helps,
Dennis