NEW APPROACH TO EXPERIMENTAL DESIGNS FOR SELECTION STUDIES IN DAIRY CATTLE AND OTHER SPECIES

Designs are described that enable measuring direct and indirect response to selection from measurements on progeny of successive bull groups. New bulls are introduced each year for two or three years of matings with the first bull group being repeated at the end of the experiment. Cows are assigned to bull groups at random by using the same sire again to mate cows that produced a female calf and a sire from the new group of bulls to mate cows that produced a male calf. Thus, numbers of full-sister progeny are maximized to enable genetic load estimates from comparisons of repeated successful matings and untested matings. Progress from male and femaie selection can be measured independently. Expected standard errors for estimates of genetic progress are presented for any number of years and daughters per year. Applications of the designs are described for both closed-herd selection and for using experimental herds for monitoring progress from bull selection by artificial insemination units. The designs are applicable to other species despite possible maternal effects, but assume that selection is continuously in one direction. © 1969, American Dairy Science Association. All rights reserved.