BLOODLINE PREFERENCE
CHANGE IN SELECTIVE CONDITIONS LEADS TO CHANGE IN
Data in these charts comes from the Trinity College genetic study led by E. P. Cunningham (“Microsatellite diversity, pedigree relatedness and the contributions of founder lineages to Thoroughbred horses,” Animal Genetics, December 2001). When change in selective conditions is overlaid (gray and yellow zones), the reason for the switch in popularity of Eclipse- vs. Matchem- and Herod-line sires becomes clear. Note the 30- to 50-year lag time. Fashions for mares are much less clear-cut than those for stallions, and even the most popular dam (Tregonwell’s Natural Barb mare) holds a frequency of only 16 percent. This indicates that allelic variation is highest in mare lines, perhaps because breeders have continued to try to “outcross” by using a wide variety of mares.