Honestly ... nostalgia. And to have another foal to have from birth.
I've had my gelding since he hit the ground. We had his mother, grandmother, aunt, sister, uncle, father, grandfather and great-grandfather ... so I grew up with a family of horses in my life. When my family talks about "the horses", it's like we are talking about family. I grew up on a cattle farm.
My boy is the last of that family of horses, and he is around 20 now. This mare is my only other horse and I just had the spark of an idea of starting another family of horses ... but I don't have cattle anymore so it would just be to have another horse since they are getting older.
She is papered (I just don't have them yet). Her bloodlines are supposed to be good, but I've never really cared about that ... like I said, the horses were our family. They were amazing, well trained/bred Arabs and I still have their papers. But I wouldn't have sold them for any amount of money. I wouldn't be breeding her to sell the foal, just to have another horse from birth.
After reading all of these replies, I think I'm sold on buying a foal or young horse. It would be too risky for her, and possibly above my expertise to care for an older pregnant mare.
Thanks for all the replies!!
