Importance of hybrid vigor or heterosis for animal breeding

Abstract

The aim of this review is to compile the importance of heterosis for animal breeding. It should be thought that the heterosis observed in animal breeding is the increase in vigor that is seen in progenies of mattings of diverse individuals from different species, isolated populations, or selected strains within species or populations. Heterosis has been of immense economic value in agriculture and has important implications regarding the fitness and fecundity of individuals in natural populations. The amount of heterosis that is realized for a particular trait is inversely related to the heritability of the trait. This is logical since traits that are lowly heritable have a small additive component (proportionally speaking) and crossbreeding takes advantage of dominance and epistatic effects. There are three main types of heterosis including individual heterosis which are increased weaning weight, yearling weight and carcass traits. The second one is maternal heterosis which is the advantage of the crossbred mother over the average of purebred mothers. Maternal heterosis comprises younger age at puberty, increased calving rate and survival of calf to weaning, pounds of calf produced in lifetime, higher weaning weights, greater longevity in the dam and other reproductive traits. The third one is paternal heterosis which is the advantage of a crossbred sire over the average of purebred sires. Similarly, there are three theories of heterosis: Dominant, Over Dominance and Epistasis theories. Dominance theories are the dominance hypothesis attributes the superiority of hybrids to the suppression of undesirable recessive alleles from one parent by dominant alleles from the other. On the other hand, Over Dominance is the interaction between genes and it results in the heterozygous individuals being superior to the best homozygous parent. Epistasis is the effect of genes resulting from the new combination of genes from different loci.

Keywords: Cross-breeding, heterosis, dominance, epistatic, hybrid vigor, importance.