Feed them in the trailer, make it nice and inviting! I put them in the trailer the evening before they go with just water. I also tag them then, it's such a quick process that they scarcely have time to squeak before it's done and forgotten about. If you're worried about anything ask someone who knows to give a hand, nobody will mind helping out a first-timer.
A thing I also find helps (apart from my niece, Dolly, bless her dear heart) is to be at the abattoir just before it opens, then you will have time to reverse, unload and get your pigs into lairage before things get busy and bustly. Also your pigs will be first through and by the time you get home will be gone.
Never easy but if you eat meat must be done. Good luck and
