Estimation of Population-Specific Genetic Parameters Important for Long-Term Optimum Contribution Selection-Case Study on a Dairy Istrian Sheep Breed

The Istrian sheep breed has been subjected to selection for dairy traits for more than two decades. However, a detailed study of some important population-specific parameters such as effective population size (N-e) and connectedness between flocks has never been carried out. The aim of the study was to examine the above parameters in dairy Istrian sheep subjected to a national selection program. The N-e was estimated as the mean rate of increase in coancestry, and connectedness was determined using four different statistics. The N-e was estimated at 73 animals with pedigree constraints imposed on 4 equivalent generations and 3 full generations. Analysis of Delta N-e ("sliding window approach") revealed a negative Delta N-e indicating a progressive loss of genetic variability (Delta N-eNEG >= 4 = -6.6, p < 0.01; Delta N(eNFG >=)3 = -4.9, p > 0.05). The overall connectedness ((r) over bar similar to 0.0001) was below the acceptable level for unbiased ranking of the animals belonging to different flocks (r(i,j) = 0.05). OCS appears to be the best option for the long-term survival (self-sufficiency) of the breed, but genetic links between flocks need to be strengthened to allow unbiased ranking of the animals based on the estimated breeding values.