Abstract
The data consisted of race records of 3 through 5-year-old Finnish Standardbred trotters (n=2637) and of 4 through 6-year-old Finnhorse trotters (n=2207). Heritability estimates for the traits studied were distinctly larger in Standardbred trotters than in Finnhorses. The largest heritability estimates of the traits in both breeds and in different age classes were observed for best time (0.09–0.52), and the lowest for number of starts (0.02–0.13) and for age at first start and age at best time (0.06–0.13). Repeatabilities of the traits were moderately large ranging between 0.24 and 0.68. Largest repeatabilities were observed for best time on volt-start. In general, young age at first start was associated with superior performance. The performance of one season at young age was highly correlated with the performance of the career over the first three years.