Heritabilities of Annually Summarized Race Records in Trotters1

Abstract

Race records of 4-, 5- and 6-yr-old Finnish Horses and of 3-, 4- and 5-yr-old Standardbred trotters from the years 1974 to 1983 were used to estimate distributional properties and heritabilities (h2) for 13 traits, and phenotypic correlations among the traits. Traits represented a horse's annual racing performance based on number of starts, percentage of placings, earnings and best racing time. The number of horses and the number of progeny groups in one age class varied from 2,232 to 3,452 and from 138 to 198, respectively. The coefficient of variation (CV) for the square root of annual earnings per start was about 67% in both breeds, as compared with a CV of 7.7 and 5.9% for best annual racing time on volt-start in Finnish Horses and Standardbred trotters, respectively. Frequency distributions for all traits departed (P<.05) from the normal frequency distribution. The distribution of best annual racing time was, however, approximately normal and distributions of transformed earnings approached approximate normality. Averages of h2 weighted over the three ages were .10 for number of starts in a year, .16 for percentage of first placings in a year, .22 for percentage of first to third placings in a year, .27 for square root of annual earnings per start and .29 for best annual racing time on volt-start in the data for Finnish Horses. In Standardbred trotters, estimates for the previous traits were .06, .16, .18, .29 and .25, respectively. Standard errors of heritability for the previous traits ranged from .03 to .06 within age groups in the two breeds. Estimates of phenotypic correlations among the annually summarized race records were all favorable with respect to a selection objective for trotters.