This may be good in a desirable trait, or it could be bad. Certain ancestors have proved to be prepotent, or capable of perpetuating their traits in their offspring. A few notable examples include the Arabian Bask, the French jumper Galoubet, and the Morgan's foundation sire Justin Morgan. In the Thoroughbred, the Dosage theory is based on a list of prepotent sires. A point system predicts the racing ability of a mating.
Breeders debate the success of line breeding vs. breeding type to type.
No one knows for sure the results of crossing one horse with another, but analyzing the ancestors can help you make more practical predictions. Most individuals are healthier when they have a limited number of homozygous genes. The heterozygous genes tend to have more heartiness, more vigor, and are more reproductively sound. In analyzing a pedigree, realize that some lines carry negative traits, such as gene-linked diseases. Ewart noted that you might be able to track this inheritance by examining the sire and dam.