engleski

Estimation of genetic connectedness between flocks in population of Istrian sheep

Recent selection strategy in flocks of Croatian autochthonous Istrian sheep breed has been directed towards improvement of dairy traits (milk, fat, and protein yields). A pedigree based BLUP was established decade ago to support the breeders with the estimated breeding values (EBVs) of dairy traits. However, EBVs have been a major selection tool only sporadically, mainly in conscientious and ambitious breeders, leading to the slow genetic improvement of the entire population. In order to provide more prominent and consistent selection progress of the population, breeders should act more synergistically and follow a unique set of recommendations given by the authorities. The out-crossing is not an option in this population in order to preserve the integrity of the breed, so all measures must be taken for sustainable across-flock genetic evaluation and selection system. One of the frequently addressed obstacles for successful across-flock genetic evaluation in sheep breeding programs is “poor” connectedness between flocks, mainly due to the lack of artificial insemination and limited exchange of breeding animals (rams) between flocks. This indirect measure for unbiased ranking of animals belonging to different flocks (connectedness) has never been examined in this population. Therefore the aim of the study was to examine the degree of connectedness using specially designed tool for this purpose (R package “GCA”). The prediction error variance (PEV) of differences in EBVs between animals belonging to different flocks was used in the analysis of connectedness. It is considered as the most computationally expensive, but the most accurate statistic for this purpose. The PEV of the EBVs was obtained from the diagonal elements of the inverse of the coefficient matrix. The pairwise PEV differences (PEVDs) were first computed at the individual level, and thereafter summarized at the unit level. The focus in the analysis was laid on 14 flocks currently participating in the national breeding program. Additional flocks were included in the analysis as well due to their historical contribution to the formation of genetic links. The analysis revealed gradient of connectedness (pair-wise estimates ranging from 0.75 to 0.82) with an average estimated at 0.78. The obtained results are informative in term of detecting flocks that share more genetic material, and therefore represent better candidates for fair joint across-flock evaluation. However, due to absence of the benchmark for this statistic, it is not possible to explicitly measure bias of comparisons of EBVs of the animals belonging to different flocks. Regardless of all, specially designed breeding schemes should be used in order to provide and maintain connectedness in this population in order to provide favourable population structure for joint across-flock evaluation system.

Istrian sheep, dairy traits, genetic evaluation, connectedness

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