THE EFFECT OF INBREEDING ON RACING PERFORMANCE IN NORWEGIAN COLD-BLOODED TROTTERS

The effect of inbreeding, i.e. the inbreeding coefficient, on racing p erformance, as measured by accumulated, transformed and standardised e arnings (ATSE), was estimated either by linear or curvilinear regressi on, one variable at a time, in univariate animal models. The statistic al model included, in addition, the effects of sex and birth year. Fou r ATSE variables, with information on earnings summed up over age-clas ses 3, 3-4, 3-5 and 3-6 years of age, were analysed. Only performances for horses born from 1972 onwards were used. For each animal, five in breeding variables were calculated utilising ancestors for two (F2), t hree (F3), four (F4) and five (F5) generations or all available pedigr ee information (FTOT). Number of records used in analyses of ATSE3, AT SE3-4, ATSE3-5 and ATSE3-6 were 7866, 7866, 6825 and 5907, respectivel y. The estimated regressions, transformed to the standardised normal s cale, were negative showing that racing performance was depressed by i nbreeding. The best fit was for curvilinear regression. The pattern ma de up by the estimated regression coefficients indicated that selectio n was able to arrest some inbreeding depression over the first four ge nerations, most likely due to recessive mutations, while additional pu rging of assumed mildly recessive mutations was shown to be a slower p rocess. (C) Inra/Elsevier, Paris.