The influence of a cow s PTA on relatives is like a ripple on a farm pond, ever wider in its influence, but less dramatic in impact as more and more remote ancestors and descendants are affected by her evaluation. The use of related animals is so complete that every animal evaluated by the animal model traces back to some unknown ancestor on every path. Unknown has a special definition in the animal model. Animals with only one progeny and no records are considered to be unknown because they do not contribute to new information or to relationships between animals with records or progeny. Cows with records but no sire identification are eliminated and become unknowns.
Unknowns contribute something to the animal model, however.
By forming groups of such animals and keeping track of genetic merit of descendants from these groups, the animal model can make a fairly reasonable guess about the genetic merit of the unknowns themselves. These guesses, properly weighted, are used in evaluating each animal further downstream. The actual impact of all these relationships on any animal s PTA under the animal model depends on other information available. Remote ancestors contribute little to evaluations, especially relative to information such as a large group of daughters on an AI sire. The animal model properly weights each item of information relative to other indicators of merit on each cow or bull evaluated.