Pedigrees of a reference population of 1 659 North American Norwegian Fjord horses were traced to founders and analysed for coefficients of inbreeding and genetic variability. Effective population size was 207.8 and there were 641 total founders. Pedigree completeness was close to 100 percent for 6 generations, with 9.8 average complete generation equivalents. The average inbreeding coefficient was 3.2 percent for the entire pedigree and 1.6 percent for pedigrees traced back five generations. Average inbreeding coefficients by year of birth increased until 1983, before decreasing and then stabilizing through 2009. Effective number of founders, ancestors and genomes were 96, 30.0 and 12.7, respectively. Low effective number of founders and ancestors indicate that genetic diversity has been lost in the development of the breed in North America. However, registry-enforced breeding strategies have contributed to lower inbreeding coefficients in the current generation.
