The use of hybrid bulls may not be a crossbreeding system in the strictest sense. The development of a true composite line of cattle is not easy. Composite breeders must make a tremendous effort to maintain large herd size with adequate representation of genetics for each breed used in the composite. Inbreeding must be avoided to retain high levels of heterozygosity and heterosis in composite breeds. Seedstock producers should study the variety of breeds currently available before beginning the challenge of constructing a new composite.
Composites are difficult to develop.
Therefore, before developing one, breeders should investigate existing breeds to see if there are already cattle available to use in a specific environment and that are market-desirable. The genetic basis for heterosis is the opposite of the origin of inbreeding depression. Inbreeding tends to cause more gene pairs in an individual to be homozygous. In contrast, crossbreeding tends to cause more gene pairs to be heterozygous. Breeds that are genetically diverse tend to cause more heterozygosity and more heterosis when crossed.