Features of bovine leukosis manifestation on the territory of the Republic of Tuva

   The peculiarities of bovine leukosis virus (BLV) manifestation on the territory of the Republic of Tuva for 1974–2023 have been revealed. Epizootologic indicators of the disease status, epizootic index and nidus index have been established. During the whole period of observation leukosis has not been registered on the territory of 7 highland and remote districts. One of the features of the well-being of highland and remote areas are natural and geographical conditions (isolated location surrounded by mountains occupying 80 % of the region's territory, limited connections with other regions, difficult accessibility). Another peculiarity is free range animal husbandry, mainly indigenous cattle on fodder, with frequent changes of pastures and free keeping of cattle. With the expansion of economic ties, importation of pedigree dairy cattle from the neighboring regions (which, according to the results of the studies, are unfavorable in terms of bovine leukosis), the epizootic situation became unfavorable. This is the main feature of the region's leukosis adversity. Leukosis registered mainly in the central districts located in the flat territories of intermountain basins, where there are favorable conditions for maintenance and feeding of dairy cattle. Under joint conditions of keeping and exploitation there is a risk of infection of other animals, which is also a feature of leukosis on the territory of the Republic of Tuva. Bovine leukosis was first registered in the Ulug-Khemsky district at a dairy farm in 1977 in a cow of the Holstein Friesian breed. Out of 50 years of observation, 11 leukosis-affected districts (Tandynsky, Pii-Khemsky, Kaa-Khemsky, Chedi-Kholsky, Ulug-Khemsky, etc.), totaling 60 leukosis-affected points, have been registered in the republic for 29 years. 914,638 animals were examined, 845 animals were found to be positive, or 0.09 % of the total number of the livestock examined in the country, the disease status was noted in 40.8 %, the epizootic index (EI) for 50 years of observation amounted to 1.2 units, the nidus index (NI) – 14.08 seropositive animals per 1 unfavorable location. Sporadic and isolated cases on the territory of the remaining 6 unfavorable districts (Barun-Khemchiksky, Sut-Kholsky, Kyzyl, Kyzyl city, Tes-Khemsky, Tojinsky) are also associated with the importation of breeding cattle, where with the implementation of diagnostic and other anti-epizootic measures, the situation, without epizootic and geographical development, rapidly improved. The Republic of Tuva has been free from bovine leukosis since 2022.

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