FERTILITY HAPLOTYPES HH IN HOLSTEIN CATTLE: MOLECULAR GENETIC BASES, DISTRIBUTION, AND CONTROL STRATEGIES

Abstract

Intensive selection of the Holstein cattle breed, aimed at maximizing milk production and improving conformation traits, has led to a significant increase in inbreeding and the accumulation of deleterious recessive alleles in the population, which negatively affect the reproductive performance of animals. Among the most studied and economically significant genetic anomalies are the fertility haplotypes (HH – Holstein Haplotype), which in the homozygous state cause embryonic and postnatal lethality, and in the heterozygous state substantially reduce herd reproduction rates. This review systematizes and summarizes current data on the molecular basis of HH1–HH7 haplotypes, their population dynamics and distribution in global Holstein cattle populations, and also examines in detail approaches to genetic monitoring, DNA diagnostic methods, and breeding strategies aimed at minimizing the economic losses associated with these lethal alleles. Special attention is paid to the results of screening studies in cattle populations of the Russian Federation.