USE OF INBRED SIRES IN CATTLE IMPROVEMENT

Results are presented of investigations on growth, semen production an d progeny testing of 122 Black Pied inbred bulls from East -Germany wi th inbreeding F of 25 %; 12,5 % and 6,25 %, respectively, and of their 114 non-inbred controls (contemporary paternal half-brothers). The in bred bulls showed depressions in daily gain of 0,3-0,4 % per 1 % inbre eding increment and poorer semen production. This resulted in delay in their use, and in lower number of sperma doses. Progeny testing was e valuated with the CC-test and for 134 bulls additionally by BLUP. Alth ough progeny performance level was only average, the 25 % inbred bulls differed from their controls. The variability of their breeding value s was increased, with more good and more poor sires. A simulated selec tion (SI = 12%) revealed potentially higher selection differences in t hese bulls compared with their controls. On average the inbred bulls r anked better than their controls (not for F = 12,5 %). The bulls with a high level of inbreeding (F = 25%) ranked frequently on lower and on higher places than their controls.