Abstract
Genetic parameters for age at first calving, and reproductive traits of cows and yield traits from first to third parities were estimated by an animal model via a two-trait analysis. Lactation records and reproductive records from Hokkaido Dairy Milk Recording and Testing Association, and pedigree records from Holstein Cattle Association of Japan, Hokkaido Branch were used. Due to the limitation of the performance of the computers, ten data subsets that contained about 100,000 records were randomly extracted by herds from the data sets, and each subset was analyzed by the AIREMLF90 program. Heritability estimates were 0.22 for age at first calving, and 0.03 to 0.05 for the reproductive traits of cows. Genetic correlations between age at first calving and reproductive traits of cows were low, while those of age at first calving and yield traits for the second and third parities were − 0.3 to − 0.4. Because of the favorable relationships of age at first calving with yield traits at the second and third parities, it was suggested that the selection by the age at first calving was effective for improvement of the long-term productivity for cows.
