Li et al. Genetics Selection Evolution 2010, 42:32 http://www.gsejournal.org/content/42/1/32 investigated here, no contrasting differences in growth, lactation or reproduction was observed. In addition, a recent study on the evolution of the cytoplasmic domains of the growth hormone receptor gene in Artiodactyla (see [61]) has suggested that possible effects of selective sweeps on growth hormone receptor gene in bovine occurred before domestication and not among the domestic breeds. Unfortunately, due to the lack of information on the mutation and recombination rates, as well as the effec- tive population size for these data, estimation of the selection coefficient is not possible here (see [59]). Given that the genomic interval of significant LD is comparable with the findings of hitchhiking around two anti-malarial resistance genes in humans [58] and microsatellite hitchhiking mapping in the three-spined stickleback [59], the hitchhiking selection in this geno- mic region might be fairly strong. Moreover, the avail- ability of genomic resources (e.g. NCBI Bovine Genome Resources; http://www.ncbi.nlm.nih.gov/projects/gen- ome/guide/cow/)in bovine makes it possible to develop more precise approaches with other much more fre- quent markers such as SNP. Genotyping an additional set of high density SNP between AGLA17 and SOD1 markers in the populations investigated will definitely give more precise information on selection and LD in the region. Because the populations studied here are not experi- mental, they differ for many characteristics other than the polled and horned traits. Thus, some of the genetic differentiation could have been due to other selective forces, e.g. pathogens. In addition, since our data violate at least partly the model assumptions of equal popula- tion size and migration rates between populations for the FDIST2 test, the outliers from the test alone should be considered with caution although the multiple neu- trality tests based on different assumptions and para- meter estimation can minimize the possibility of false positives. Moreover, selection is not the only possibility for changes in the distribution of variation to occur at particular loci, reduced variation or increased differen- tiation can result from chance alone, e.g. genetic drift, bottlenecks or founder events [57]. To obtain clear evi- dence for selection of these markers, we must analyze nucleotide variations between polled and horned populations. Conclusions Our microsatellite data from northern Eurasian cattle populations empirically indicate a practical approach for identifying the best candidate loci under hitchhiking selection by simultaneously applying multiple neutrality tests based on different assumptions and parameter esti- mations. By analyzing microsatellite markers adjacent to Page 12 of 14 functional genes, we identified two loci (SOD1 and AGLA17) that are “selection candidate” targets asso- ciated with the horned/polled trait in cattle. This result could be further confirmed by using a more densely spaced set of markers. It would also be of great interest to see if similar patterns of selection around the POLL gene are observed in commercial beef breeds such as Australian Brangus, Angus and Hereford breeds, where dehorning and breeding practices for polled cattle have been an accepted part of cattle management for genera- tions. Another future challenge is to verify the signal of artificial selection on the POLL gene, possibly using the next generation sequencing technology to detect the nucleotide variation of the gene between polled and horned cattle. In addition, the approach we have taken in this paper can be easily extended to other cases and marker types. For example, diversity among cattle has been directed by man towards different goals (e.g. draft, milk, meat, fatness, size, color, horn characteristics, behavior, and other characteristics) during many genera- tions of selection. Each of these selection events has potentially left a signature of selection on the genes and their neighboring loci that could be detected by using tests such as we have applied here. As a marker technol- ogy, SNP would offer the advantage of higher through- put when scanning the genome for evidence of hitchhiking selection. Acknowledgements The study includes parts of the data sets from projects of SUNARE (Sustainable Use of NAtural REsources; http://www.aka.fi/sunare), Russia In Flux, and N-EURO-CAD (North European Cattle Diversity). The projects were funded by the Academy of Finland, the Ministry of Agriculture and Forestry in Finland, the Nordic Gene Bank for Farm Animals (NGH), and the Nordic Council of Ministers. We also thank Tatyana Kiselyova, Zoya Ivanova, Ruslan Popov, Innokentyi Ammosov, Elena V. Krysova, Nikolai G. Bukarov, Aleksandr D. Galkin, Boris E. Podoba, Ljudmila A. Popova, and Valerij S. Matjukov for their help in collecting the samples. Authors’ contributions MHL designed the study, performed the data analysis and wrote the manuscript. TI-T did the laboratory work and contributed to the manuscript writing and data analysis. HL did the laboratory work, contributed to the manuscript writing and data analysis. JK planned and coordinated the whole study, and contributed to the manuscript writing. All the authors read and approved the final manuscript. Competing interests The authors declare that they have no competing interests. Received: 6 April 2010 Accepted: 6 August 2010 Published: 6 August 2010 References 1. Kantanen J, Olsaker I, Holm L-E, Lien S, Vilkki J, Brusgaard K, Eythrosdottir E, Danell B, Adalsteinsson S: Genetic diversity and population structure of 20 North European cattle breeds. J Hered 2000, 91:446-457. 2. Li MH, Tapio I, Vilkki J, Ivanova Z, Kiselyova T, Marzanov N, Ćinkulov M, Stojanović S, Ammosov I, Popov R, Kantanen J: Genetic structure of cattle populations (Bos taurus) in northern Eurasia and the neighboring Near