The first genetics class I had was an Agronomy class. It covered plant and animal genetics, but one of the things that stuck in my mind was the process plant breeders used to develop hybrid seed corn. They developed a variety of corn by practicing inbreeding to develop that line then they crossed that line on another unrelated variety of inbred corn. This process produced a high-quality seed corn that produced high yields that the American farmer is noted for. That was my introduction to hybrid vigor.
Hybrid vigor carries over into animals with the phenomenon that results in offspring that are superior to the parents. It works in a similar pattern, as the breeder crosses two individuals that are unrelated through several generations. They then achieve hybrid vigor through this process – improving their horses. This is referred to as breeding up, as the stallion is selected based on how he could improve the mares. The complimentary effect. This is also called outcrossing to get hybrid vigor.
The genetic definition of outcrossing is “the mating of two unrelated individuals from the same breed.” This is the mating of individuals within a breed that show no close-up relatives in the pedigree. We have to remember that many breeds are formed through inbreeding to one or a few common ancestors and that means we may eventually get to some common ancestors in the pedigree.
It can be as simple as a breeder starting with a set of mares that he crossed on a stallion. Then he would retain several daughters and they would be bred to another unrelated stallion. Some breeders practiced inbreeding to set the type they were looking for in their horses before outcrossing them. They inbred to their stallion and his daughters or granddaughters. Then they outcross those inbred mares on…