Individual-based assessment of population structure and admixture in Austrian, Croatian and German draught horses

All over Europe, the number of draught horses has decreased drastically during the last 50 years. As a prerequisite for efficient management decisions, we analysed the conservation status in Austrian (Noriker Carinthia - NC, Noriker Salzburg - NS), Croatian (Croatian Coldblood - C, Posavina horse - P) and German (Altmaerkisch Coldblood - A, Black Forest horse - BF, Mecklenburg Coldblood - M, Rhenish German Draught horse - R, Saxon Thuringa Coldblood - ST, Schleswig Draught horse - Sch, South German Coldblood - SG) draught horses (434) using multilocus genotypic information from 30 (effectively 27) microsatellite loci. Populations located in areas with less intensive agricultural production (C, NC, NS, P and SG) had greater diversity within the population and estimated effective population size than A, BF, Sch, M, R and ST populations. The PCA plots revealed that populations form five separate groups. The 'Noriker' group (NC, NS and SG) and the 'Rhenish' group (A, M, R and ST) were the most distinctive (pairwise F(ST) values ranged from 0.078 to 0.094). The 'Croatian' group (C and P) was in the centre, while the BF and Sch populations formed two out-groups. A posterior Bayesian analysis detected further differentiation, mainly caused by political and geographical factors. Thus, it was possible to separate the South German Coldblood from the Austrian Noriker population where no subpopulation structure was detected. The admixture analysis revealed imprecise classification between C and P populations. A small but notable separation of R from A, M and ST populations was detected, while Sch and BF populations remained as out-groups. The information obtained should aid in making efficient conservation decisions.