I need some advice or suggestions for keeping a horse calm while being trailered. My mare gets extremely agitated while traveling and ends up soaked in sweat by the time we arrive at our destination. She is not scared of the trailer at all. She loads exceptionally well, unloads easily, and will munch hay while in the trailer. She has been trailered extensively throughout her entire life. We have traveled basically all over lower Michigan for different shows and trail rides. She has been on probably 10-30 trailer rides each year for the past 15 years, varying lengths from 5 minutes down the road up to 4 hours away. She doesn't pull or rear in the trailer, but does paw. I think she just paws and shakes herself into a frenzy. If the ride is over 30 minutes, she will be dripping sweat by the time we arrive. This is in any weather. She does do much better with another horse trailering with her, but this is often not an option.
I have tried ear plugs, but she has always managed to shake them out. I am considering trying calming supplements because I feel like this level of sweating is extremely unhealthy and will be detrimental to her performance as well. I don't want to give her any supplements that will actually sedate her though because I feel like that will also be detrimental to her performance.
Any advice will be so appreciated! I am just at a loss for ideas.