Surely the transporter has guidelines for this? They may have previous experience of moving youngsters, why not give them a call and see what they say?
Travelled my baby 6 hrs at 3 months old, but with Mum obviously. He was happy as larry, space to lie down and eveything. Next long trip was about 3 months after weaning at about 15 months old, again with Mum and again about 6 hours but this time standing up in a partition like a 'proper' horse. Again happy and no ill effect (although travelling is much harder work on youngsters) He travels great now (age 5)! That's just my personal experience.
I am sure the transporter has.I was looking at a foal but it is in Wales(not weaned yet) and I'm in Scotland so just thought maybe not fair on horse.Would it be too taumatic for a foal?Would have stop offs on way but still......................
Am just trying to cover everything before go further.
My friend bought a foal in Germany, so he travelled to the UK at 7 months old with a professional transporter. He is now 5, and has never had a problem with loading/travelling. On the other hand, I also know someone who got a weanling and travelled him 1 hour in his own lorry. Said person is a crap driver and traumatised foaly so much he had real problems getting him to load and travel well again.
Guess what I'm saying is, for a precious cargo like that on a long journey, leave it to the experienced professionals!!