Introduction. The effectiveness of breeding work of an agricultural enterprise is characterized not only by the presence of high-yielding mares in the dairy herd, but also by the technologies used in the industry. The most important task of the industry is to provide dairy herds with replacement young stock with high genetic potential. Objective. The purpose of this study was to determine the productive and economic indicators of the most highly productive mares of the Russian Heavy Draft breed and compare the obtained data with the average values for the studied population. Material and methods. On the population of Russian Heavy Draft horses of the Republic of Mari El, the productive and economic indicators were studied in 213 mares culled from the dairy herd in the period from 1998 to 2023. Results of the study, discussion. The studies showed that 17 % of the population of mares in the dairy herd had a milk yield of more than 5,000 kg of milk per lactation, which allows us to classify these mares as record holders. The average milk productivity of the record-breakers was 5,550 kg of milk with a variability of 34 %. The mass fraction of fat and protein in the record-breakers was 11 and 3 % lower than the average values for the population, respectively. The service period duration increased from 62 to 173 days with an increase in milk production. The milk production coefficient of the record-breakers was 856 kg, which exceeded the average value for the herd by 36 %. The lifetime productivity of the record-breakers was 44 % higher than the average value for the population. The record-breakers were characterized by higher growth energy, as a result of which their first fruitful insemination was carried out 175 days earlier than the average for the population. Conclusion. Due to long-term selection and the focus of breeding work, the record-breaking mares accumulated a large number of genes influencing milk production in the genotype. The presence of a large number of record-breaking sows indicates the genetic potential of the dairy herd and is extremely necessary for improving the productive and breeding qualities of the population.