The Superior Genetic Source for Optimum Crossbreeding Performance

Eight distinct breeds of swine are recognized in the United States and records of the ancestry are recorded in their respective breed associations. Whereas several of these breeds were introduced from Europe and others developed here many years ago, all have undergone significant change and improvement since their establishment and/or introduction to the U.S. They are now truly U.S. breeds. Each of these breeds has been developed through the united efforts of resourceful private breeders working in concert with their various breed societies. Distinct breeding goals were envisioned and selection objectives pursued in improving animals in the economically important traits. This was accomplished under a wide variety of climatic conditions, nutritional environments and management systems. Common breeding goals have produced animals consistent in structure and form. Mild inbreeding and strong selection efforts have characterized this breed development, the consequence of which are pure lines that are relatively free of genetic defects and that are capable of producing predictable, high-performing offspring. The diverse conditions under which the various breeds and lines have been selected ensure availability of individuals capable of adapting to the wide range of production and management systems that exist throughout the U.S. and base necessary to sustain continued improvement. Selection on the economically important traits has been the powerful genetic force that has permitted phenomenal improvement in each of these outstanding breeds.

Purebreeding with selection for a countless number of generations has maintained and even increased genetic diversity between breeds and increased the homozygosity and, thus, the predictability of breeds and strains. Combining these various breeds results in substantial heterosis or hybrid vigor. This superiority of the crosses above the average of the pure lines is enormous, particularly for reproductive and performance traits. For litter weights at weaning and average litter age at 230 lbs., the advantage over the purebred parental averages is in the range of 30%.

The availability of these distinct breeds provides an opportunity for maximizing heterosis at the commercial producer level. Rotational schemes involving two or more breeds can achieve nearly optimum heterosis levels and offer simple, flexible alternatives for the smaller operator, or those wishing to keep their own gilts and turn the generations quickly.

Dr. Lauren Christian, Professor of Animal Science
Iowa State University