Genetic Distance and Differentiation among Cattle Breeds in Ethiopia: A Review

Abstract

Studies conducted on genetic diversity and population differentiation of Ethiopian cattle breeds have been reviewed. Out of 22-28 phenotypically and geographically recognized cattle breeds in Ethiopia about 17 breeds were characterized at molecular level. The population differentiation indicated that Ethiopian breeds significantly differ from taurine referenced Hanwoo and Friesian breeds. They exhibit lower observed heterozygosity than Hanwoo and Friesian breeds. Most studies in Ethiopia witnessed low between breeds and high within breed variations. The genetic distance among Ethiopian breeds did not necessarily depend on geographic distance. Zero genetic distance was estimated between Boran and Horro and between Abigar and Sheko populations based on mitochondrial cytochrome b gene analysis. From Ethiopian breeds, better genetic diversity was recorded in Abergelle (0.795) than Bagait (0.590), Afar (0.559), Raya (0.582), Arado (0.636), Fogera (0.541) and Irob (0.527) breeds. Similarly higher heterozygosity was found in Horro breed (0.387) followed by Ambo (0.386), Arsi (0.376), Boran (0.374) and Danakil (0.363). The low genetic diversity and heterozygosis observed in some populations could reflect inbreeding due to uncontrolled mating. Generally the high within breed variation observed in Ethiopia cattle population could create favorable condition for further improvement through selection. In addition, the previous studies might indicate higher admixture among Ethiopian cattle populations and absence of artificial selection pressure. The study conducted at molecular level so far were fragmented and not exhaustively included all breeds that were classified by phenotype or geography. Thus it is essential to carry out further studies which encompass all breeds in order to have full picture of breed diversity and differentiation among Ethiopian breeds. Furthermore, it will have an immense impact if the studies started on molecular characterization advanced to the level of utilizing genomic information for genetic improvement, resource conservation and disease resistance.