Ooooh... this looks verrrry interesting! I'm looking forward to reading Dora's three-week perspective on life in the States. I googled the title but could find only one summary and that was on Squee's site
Perhaps livestock importation restrictions weren't as stringent in the 1970s as they are now, when it takes many months and $$$$$$$$$ to move a horse between countries. Even here a considerable amount of money, paperwork and fuss is required (legally) to transport a horse between states. I would guess, though, that there are contingencies for show and race horses that are routinely trailered around the country. MJ would know more about that.