Inbreeding, outcrossing, line breeding and hybrid vigour are well understood by racehorse breeders. When closely related individuals mate, their offspring are generally smaller, less viable or less fertile than the rest of the population. Examples of inbreeding are mating full brothers to sisters, fathers to daughters or mothers to sons. However, if two inbred groups are crossbred, the result is individuals that are often larger, stronger and more fertile; this is called hybrid vigour.
When you are breeding racehorses, the aim is to improve speed over a very specific distance. Although the outcome is a single variable measured with the modern, electronic version of a stopwatch, speed is made up of a huge number of other variables such as conformation, temperament, vitality and good health.
HYBRID VIGOUR
In racehorses, the…