This is the one reason that we are thankful that we rent many different places, and that the animals have to be trailered to and from them. The calves all learn pretty young that going on the trailer with mom is no big deal. There are always a few that balk at it, but usually will go on pretty quick.
For the replacement heifers we keep, going on a trailer just means getting to go to someplace with more grass. And the bulls all know that getting on the trailer means they are going to pasture to see the girls. Our main loading chute/alley is the width of the trailer and the back wheels drop down in the dirt in depressions that makes it not more than a few inches to step up in the trailer. There are 2 gates in the alley so that they can only go back so far and the board fence does allow for someone to climb it if necessary in a hurry. Plus is is wide enough that an animal can go by and not squeeze you into a pancake against the side.
We have often loaded a bull in the pasture just by putting some feed in the trailer and telling him to load up. Or getting him in a catch and then walking him to the trailer and him seeing a little feed in a flat black fortex type pan. Yes we have had some crazy ones but they get weeded out...and get weeded out faster and earlier as we get older and are not wanting or able to move fast enough to get out of their way.
Another thing we have found, many are afraid of slipping and don't like a "shiny clean trailer" to go into either. A little dirt on the floor, not nice clean shavings, makes it much less scary to them. A scared animal will slip faster than anything because they are in a hurry to get past the "scared part". So they hurry or try to jump and they slip. The next time it just reinforces their scared reaction.