Trends in effects of year-month on type traits in Japanese Black heifers and cows

Abstract

We clarified the factors affecting the type traits of Japanese Black heifers and cows in the Tokachi area of Hokkaido, Japan. We also showed the trends in those type traits over 30 years. The data used were the type records of 81,528 Japanese Black heifers and cows that had been registered between 1973 (2012 for final score) and 2020. Type records covered six traits, namely final score, stature, chest circumference, chest depth, rump length, and thurl width. The effects of year-month, age, herd, and classifier were estimated by using a least-squares method. The effects of age were included as a covariates with a secondorder polynomials on age in month in our mathematical models. For stature, estimates increased from 121 to 127 cm through all periods with increasing year-month. For chest circumference, rump length, and thurl width, the phenotypic trends of effects of year-month increased after 2006.