  The domestication and development of cattle has considerably impacted human
societies, but the histories of cattle breeds have been poorly understood
especially for African, Asian, and American breeds. Using genotypes from 43,043
autosomal single nucleotide polymorphism markers scored in 1,543 animals, we
evaluate the population structure of 134 domesticated bovid breeds. Regardless
of the analytical method or sample subset, the three major groups of Asian
indicine, Eurasian taurine, and African taurine were consistently observed.
Patterns of geographic dispersal resulting from co-migration with humans and
exportation are recognizable in phylogenetic networks. All analytical methods
reveal patterns of hybridization which occurred after divergence. Using 19
breeds, we map the cline of indicine introgression into Africa. We infer that
African taurine possess a large portion of wild African auroch ancestry,
causing their divergence from Eurasian taurine. We detect exportation patterns
in Asia and identify a cline of Eurasian taurine/indicine hybridization in
Asia. We also identify the influence of species other than Bos taurus in the
formation of Asian breeds. We detect the pronounced influence of Shorthorn
cattle in the formation of European breeds. Iberian and Italian cattle possess
introgression from African taurine. American Criollo cattle are shown to be of
Iberian, and not African, decent. Indicine introgression into American cattle
occurred in the Americas, and not Europe. We argue that cattle migration,
movement and trading followed by admixture have been important forces in
shaping modern bovine genomic variation.
