Connectedness among five European sport horse populations

This paper is one in a series of studies treating the prerequisites for international use of nationally estimated breeding values (EBVs) of sport horse stallions. One prerequisite for effective use of national EBVs across countries (populations) is genetic connectedness among concerned populations. Thus, genetic connectedness between five sport horse populations from breeding organizations in Denmark (DWB), the Netherlands (KWPN), Sweden (SWB) and from the two German breeding organizations Hanover (Han) and Holstein (Holst) was studied. The number of stallions in common (NSC), genetic similarity (GS), variance of the differences between estimated country effects (CEV) in two organizations and correlation between estimates of country effects (CEC) were used as measures of the genetic connectedness between organizations. Stallions with progeny tested in performance tests for young horses in at least one of the five organizations were used. The material included 2457 stallions, born between 1952 and 1997, for which 49 446 progeny had been tested in the five breeding organizations. The numbers of stallions with offspring that had been tested in two, three, four and five of the participating organizations were 218, 58, 25 and 5, respectively. The material was arranged into groups according to birth-year of the stallion. Values for NSC, GS, CEV and CEC were calculated for each group to investigate whether there was any difference or trend in genetic connectedness over time. The same measures were also calculated for the whole data-set, considering all available information on pedigrees and progeny. Genetic connectedness was found between all participating organizations in all groups and grew stronger over time. The results were on a similar level to or better than comparable results for Icelandic horses and dairy cattle; they suggest that estimation of genetic correlations between similar traits tested in different organizations is feasible.