Evolution of Methods for the Quantitative Assessment of Inbreeding in Livestock.

Inbreeding is a quantitative measure of autozygosity that underlies the assessment of genetic risks and the management of genetic progress in livestock populations. The development of methods for its estimation reflects a transition from probabilistic pedigree-based models to the direct analysis of genome structure. This review systematizes the evolution of approaches to inbreeding assessment-from the classical inbreeding coefficient F based on identity by descent (IBD) to marker-based, segment-based runs of homozygosity (ROH) and probabilistic homozygous-by-descent (HBD) models. It is shown that the coefficients F_ped, F_GRM, F_ROH, and F_HBD capture related but distinct aspects of autozygosity and are therefore not fully interchangeable. Particular attention is paid to the transition from integral indicators to spatially and temporally stratified analyses of autozygosity, enabling the differentiation between ancient and recent inbreeding. Methodological assumptions, limitations, and the sensitivity of various approaches to marker density, detection parameters, and population demographic structure are discussed. A comparative analysis of methods for calculating F_ROH and segment-based autozygosity is presented. The necessity of a comprehensive assessment of inbreeding and the standardization of analytical protocols for its application in modern breeding programs is substantiated.