Kind of irrelevant to your buckskin, but how do you think I feel with my black mare (left) looking like this!?! Lol CAM00081.jpg
Sweat, water, fly spry are all enough to bleach a dark coat, mane, or tail. My mare sweats a ton during hard workouts and I also spray her down after each ride so the sweat & water combo has taken a toll on her coat this year. I wouldn't doubt that maybe that could be a factor for your mare, as well at the urine. I think genetics also play a big part in color and fading. I see many black horses that don't change or fade at all, while others are barely recognizable in the summer months.