HGG Community Forums

When you put a mare into a pasture, she begins accumulating what is called a "pasture bonus." Each horse has a given breeding ability percentage which is actually a fairly broad range of potential foal abilities. For PT, for instance, a Perfect Foundation's potential foal PT range falls between 8.9 and 10.4. When you click the "breed these horses" button (or the pasture breeding program runs) a random number from the mare and one from the stallion are generated. Each one falls anywhere along the possible range, and the two are averaged to come up with the PT of the foal being produced. The same process is used to determine the foal's breeding ability, using a separate set of random numbers. (This is my interpretation of what happens based on a post about it on the old forum. Ammit probably would explain it better, and differently.)

When a mare remains in the pasture, for up to 30 days, the range of her contribution to the foal's ability gets narrower, as a bit is taken off the lower end of her range each day. The result is that her chances of producing foals at the higher end of her breeding range increases marginally. The top end of her range remains what it always was. She doesn't become a "better" breeder, she is just more likely to produce closer to the best of her given ability. After 30 days, no further changes take place, and if you remove her from the pasture, her full breeding ability range is restored and she will have a chance of producing foals from the lower end again.

My experience is that, when breeding by hand, more than half of them will be neuters by SAT, Mare Advice (or SMA), or Gelding advice. When mares have been in the pasture at least 30 days, the odds are that her foal will remain intact through those three tests. Occasionally a filly is neutered by Mare Advice, and colts fairly often do not paper or comparison test as any better than their sire's. There is no appreciable change in the chances of a foal being neutered by the consistency test.