Scrotal circumference, however, is highly heritable, and there is a growing body of evidence to suggest that the most effective way to improve inherent fertility in both males and females is simply to select for larger scrotal size. I have combined these two categories because a number of traits seem to fit in both. Adaptability traits are those which make an animal particularly suited to an environment. Included among these would be soundness, disease and pest resistance, and heat or cold tolerance. Convenience traits are those which contribute directly to savings in time, labor, drugs and facilities.
Some examples are soundness, disease and pest resistance, and temperament.
Not all the traits mentioned in the four categories above are well understood, very heritable or very variable within a breed. Their virtue, however, is that if we succeed in changing them in the direction we want, we can be sure that we have made not only change , but improvement. Clearly, this article hasn't answered the question. Someday we may have computer programs which will help answer it.