Why did you not stop her mid-stride? Something like " Mom, no disrespect intended but I really think I don't want to hear this story. You know how much I love horses and this doesn't sound as if it will have a good ending. I know your are just trying to keep me informed but this will just cause me some measure of pain and will probably give me nightmares. Thank you, I appreciate you respecting me in this. " Then smile at her and touch her arm reassuringly or something. That would probably be better for both of you and less rude then tuning her out...if your mom is anything like mine, they KNOW when you are tuning them out and it hurts them even more. Could be why she ended up going so in depth with the story...perhaps she KNEW it would push your buttons so she could get a little bit of her own back for being shut out?
Just a thought, Zoo
"If patience is worth anything, it must endure to the end of time. And a living faith will last in the midst of the blackest storm."
- Mahatma Gandhi