Using pedigree information to study genetic diversity and re-evaluating a selection program in an experimental flock of Afshari sheep

Abstract. The purpose of this paper was to evaluate the inbreeding consequences of a short-term selection experiment which was initiated in 1998 in an Afshari sheep flock. Moreover, the conducted selection experiment was re-evaluated through assessing change in ranking of the first 10 influential ancestors when their genetic contributions were replaced with their breeding values. A total of 1714 animals were registered in the herdbook with a founder population comprised of 243 animals. The average coancestry (f) and inbreeding (F) in the reference population were 2.1% and 1.2%, respectively. Estimated value of the effective population size (N_e) was 50. The effective number of founders (f_e) was estimated to be 40 and the effective number of ancestors (f_a) was 34. Estimates of breeding values revealed that owing to phenotypic selection some ancestors with lower breeding values had greater contribution to the reference genome than those with greater breeding values and, for this reason, the population has been deprived from the maximum genetic improvement that could be achieved if selection was based on breeding values. The effective number of founder genomes (f_g) was computed to be 23 and the effective number of non-founder genomes (f_ne) was 55. The index of genetic diversity decreased by almost 2.2% over the period studied. In general, decrease in genetic variability was low and N_e was not very low for a small-closed population under selection, indicating even in populations which undergo selection, besides achieving genetic gain, the rate of inbreeding is controllable if matings carefully planned.