Stallion owners nominate the stallion for a cost of $200. For this, they can designate one mare by Jan. 1 (will know by then which of their mares did or did not settle).
Mare owners bid for an additional breeding to that stallion. This is a true auction, done here on The Little Horse Barn. Some stallions sell for the opening bid of $200, and in the past we have had some that go over $1,500. The winning bidder (stallion owners may bid on their own breeding if they wish) designates one mare....which means there can be 2 babies sired by that stallion that are part of the Sweepstakes program, and can show in the Sweepstakes class as a weanling the following year. All money collected is put into a pot and because we have enough foals showing, there are typically 2 classes. Colts and fillies show in the same class. The pot (minus a few minor expenses) is divided in half (one half for each class) and foals are divided equally by height so that there are the same number of foals in each class (one year we had 7 foals that all measured 30.0" which was the dividing line and we needed 2 to go in the smaller class and 5 in the taller....so we put all 7 in a hat and drew numbers for the 2 classes). Foals are placed to 10th, and all top ten must have hair for DNA pulled at ringside. Parentage must be qualified before we pay out any winnings.
The top 8 foals in each class get a slice of the pot, and the sire of the winning foal also gets a percentage. The percentages are spelled out in the rules on the official site - address in my original post.
The value is the exposure this gives the stallion owners, the offspring they have produced in the past, and bragging rights (and added value) for those foals that win.