Date of Award
Doctor of Philosophy
Pedigrees of 440,702 males and 526,956 females born during 1960 through 1979 and registered in the herdbook of the Holstein-Friesian Association of America were examined. Annual trends in genetic merit of sires, dams, maternal grandsires, and maternal granddams were determined from estimated transmitting estimates (ETA) contained in the pedigrees. The increase in the rate of change in genetic merit of parents was associated with the introduction of more accurate procedures for estimating transmitting ability of males and females in 1967. Annual genetic change (g) in the male and female populations was estimated as the sum of annual change in average ETA of sires plus the annual change in average ETA of dams. From 1971 to 1979, g's for females were 120.5 lb milk, 3.31 lb fat, and -.0072 milk fat percent. Corresponding g's for males were 152.2 lb milk, 4.38 lb milk fat, and -.0076 milk fat percent. Additional genetic gain in milk yield was possible but not attained due to excessive selection pressure put on other traits such as body conformation;Bulls in artificial insemination (AI) organizations were superior to bulls in non-AI use. Approximately one-third of the females in the study were sired by non-AI bulls. The number of young bulls progeny-tested in AI steadily increased across birth years. Breeder-proven bulls that entered AI were genetically equal, on the average, to AI progeny-test bulls returned to active AI service. Approximately 40 breeder-proven bulls entered AI organizations each year;Pedigree information was used to investigate its effectiveness in predicting ETA's of males (sons). Regression of coefficients for ETA's of ancestors were computed within birth year of sons. When ETA's for milk yield of sires, dams, maternal grandsires and maternal granddams were used individually to predict ETA for milk yield of sons, no significant differences were observed among regression coefficients within birth years. Significant differences between regression coefficients were obtained among birth years in similar prediction equations for ETA of milk fat percent of sons. ETA's of sire, dam and MGS were the best combination of information for son ETA prediction equations. Addition of MGD information did not appreciably increase the accuracy of prediction. ETA's of sires and dams also could be used to predict ETA of milk and milk fat percent of sons with little loss in accuracy.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Katherine Louise Lee
Lee, Katherine Louise, "Genetic trend and selection practiced in the registered Holstein cattle population " (1983). Retrospective Theses and Dissertations. 8413.