May I ask what kind of spurs? Do you feel as if you can use your leg without using your spur while they're on?
In general, spurs are for refining cues--which is great when you're trying to say "this specific feeling means right versus left lead," but it can be difficult to control your lower leg if you're having a tough time. I've ridden for many years, but I've only recently started using spurs to give my horse more subtle, specific cues-- and those are little round nubs!
Some horses are just "offended," as anabel puts it, by some tools like whips or spurs. If you are using a harsher/rowel-type spur, maybe switch to 1/4" or 1/2" nub spurs. If you are already using a smaller, easy-to-control nub spur, maybe practice giving leg versus spur or just scrap the spurs altogether and try something like a dressage whip that you can apply behind your leg/at the girth to enhance your cue.
Will your horse at least pick up the canter (either lead) without spurs, just your leg?
ETA... most horses have a "preferred" lead where they balance better and find moving along much easier. For my horse, that's his right lead. That is completely normal; however, it can't hurt to have a vet take a look at the horse you're riding! Never know if it's arthritis or a little stiffness, etc.
Last edited by existentialpony; 04-07-2013 at 06:36 PM.