Contributions of Genetic and Environmental Factors to Time Trends in Milk Yield and Percent Fat in Advanced Registry Holstein Cows of Hokkaido, japan, during the 1948-1958 Period

Abstract

The time trends in milk yield and percent fat in the Advanced Registry Holstein cows of the Hokkaido region in Japan were analyzed statistically and expressed quantitatively in terms of contributions of changes in four different factors: environment, dam's birth years, sires, and towns involved.
Atotal of 2, 382 records from the same number of cows tested during the 1948-58 period were used for each trait. Regression of each trait on the year of test was estimated for each of the two divisions (1948-51 and 1951-58) of the period under observation and for each of the two locality groups (four towns of "advanced" cattle-breeding areas and the other towns), as well as for all the towns combined. Then, each of these estimates of regression was partitioned into portions attributable to the four individual factors.
The results of the analysis were presented graphically and some of the important points revealed in the analysis were discussed with special reference to the shift of the emphasis in breeding, feeding, and management from milk yield to fat percentage in response to the rising general interest in the postwar days, differences between the locality groups in rapidity and sharpness of such response, and causes of the trend of decline in milk yield during the later part of the period. The extent of genetic improvement in each of the characters in question was also discussed in relation to the trend in the actual records and contribution of the bulls imported after World War II.