AbstractA total of 13 979 Norwegian trotters were born in Norway and registered in the Norwegian Trotting Association between 1972 and 1987. The generation intervals between sire and son (n = 333) and sire and daughter (n = 4366) were 11.23 and 10.91 years, respectively. The corresponding generation intervals between dam and son and dam and daughter were 11.71 and 11.12 years. The average mating age of stallions and mares were 9.81 and 9.91 years. Since 1972, the generation intervals between sire and son and sire and daughter increased significantly. Also, the average age of stallions and mares increased in this period. On average, the stallions and mares first reproduced at 4.69 and 6.24 years of age. Mean reproductive life was 6.40 years among stallions and 5.57 years among mares. The average size of progeny groups was 39.5 offspring per sire and 3.6 offspring per dam. Over the years, the amount of total and four-generation inbreeding steadily increased in the population.