Historic Genetic Characterization of King Ranch Quarter Horses

In this investigation, a retrospective trend analysis from 1915 to the present was conducted on ancestral breeding, genetic relationships, and inbreeding of King Ranch linebred Quarter Horses. Results were from analysis of 8-generation pedigrees of 16 stallions and 74 mares used for breeding on King Ranch in 2007. A composite pedigree file (n  =  462 animals; 127  =  sires, 335  =  dams) was based on numeric codes for each animal and its sire and dam, tracing ancestry back to Old Sorrel (born in 1915). Results revealed the average influence of foundation was 89.2  ±  0.8 and 80.8 ± 1.8% (P  <  0.05), and unknown influence was 31.7  ±  3.3 and 27.2  ±  1.1% (P  >  0.10) for stallions and mares, respectively. Computed mean genetic relationship coefficients of stallions and mares, respectively, to Old Sorrel were 6.4  ±  1.0 and 10.8  ±  0.6% (P  <  0.01), those to Mr. San Peppy were 13.4  ±  2.1 and 21.6  ±  1.38% (P  <  0.01), and those to Peppy San Badger were 25.2 ± and 27.2  ±  1.3% (P  <  0.10). Mean inbreeding coefficients for stallions and mares were low, at 1.6  ±  0.7% and 3.49  ±  0.5%, respectively. Application of these procedures to other horse lines and breeds is of potential value to maintain genetic integrity and relationships while minimizing inbreeding.