Heterosis is created when unrelated breeds are crossed. The lower the relation between breeds, the higher the heterosis that you get. The effects of heterosis are the opposite of inbreeding depression. Research indicates that heterosis really improve traits like vitality, fertility, health and survival allowing also higher production then parent average. Inbreeding leads to depression, mainly in the secondary traits. Heterosis is the extra added genetic value that is generated above the parent average (see Graph. 1).
Graph. 1: Effect of heterosis
The additive breed effects are important in crossbreeding as well as in all breeding. The heterosis is an extra benefit on top of the parents average. Using the best breeds and the best bulls in these breeds is essential for successful crossbreeding. A crossbreeding program needs to be well planned and organized to produce benefits. ProCROSS is the combination of three unrelated, productive and very competitive breeds, all with efficient breed improvement programs.
Capturing and sustaining heterosis is a key part to an efficient crossbreeding program. Once you experience the extra bonus of heterosis, you do not want to go lower than 75%. Only using 2 breeds the heterosis will drop to 50% in the second generation – leveling at 67%, in future generations. A system of 4 breeds results in an even higher heterosis leveling at 93%. But it is very hard to find 4 competitive, unrelated breeds that produce sufficient milk. ProCROSS is a 3-breed rotation system generates optimum results with an average heterosis of 86%.