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.

Automated summary

The study examined the effective population size and connectedness between flocks of dairy Istrian sheep, revealing a progressive loss of genetic variability and overall low connectedness. To ensure the long-term survival and self-sufficiency of the breed, genetic links between different flocks need to be strengthened.