Yes, it's usual to have a solid-sided race. If you have it just wide enough for your sheep, so they can move along it comfortably in single file, but cannot get in two abreast and cannot turn round, that makes it simpler for dosing on your own. If you aren't tall enough to reach over from the outside to dose sheep in the race, then you need a slightly wider race so you can get in alongside them - but then you will get a bit of shuffling and turning around.