One of the main characteristics of modern agriculture is the enormous increase in livestock performance, which damages fertility and health. Genomic breeding methods, combined with selection indices, can enhance traits that have suffered from unilateral selection pressure. Introducing feed efficiency into breeding is one of the milestones in modern dairy cattle breeding. An indicator that captures the differences in the metabolism of dairy cows and is applicable for breeding for feed efficiency is residual feed intake. It is independent of body size and performance and represents differences between dairy cows in basic metabolic processes. Determining feed efficiency for an individual cow is linked to measuring its feed consumption, requiring individual feeding boxes with electronic cow identification and feed weight recording. This labour-intensive and costly procedure is not feasible when feeding cows in groups on production farms. Therefore, cheaper procedures are being sought to measure feed intake or to determine properties directly associated with feed efficiency. One of the options is to use infrared spectrometry for milk as a cheap predictor for cows. In the case of obtaining phenotypes for feed efficacy traits based on milk spectrometry, it is possible to use a genomic approach to estimate genomic breeding values. The genomic approach makes it possible to use a subset of animals with phenotypes for feed efficacy traits and genotyped animals as representatives of the whole population and to obtain breeding values for the rest of the population.