The purpose of the research is studying the distribution of endoparasitoses in bison in various regions of the Russian Federation.Materials and methods. The endoparasite fauna in bison was studied in 2018–2020 in the FSBI Prioksko-Terrasny Nature Biosphere Reserve (Moscow Region), the Bison Nursery of the Siberian Branch of the Russian Academy of Sciences of the Altai Republic, the Bryansk Forest Nature Reserve (Bryansk Region), the Ugra National Park (Kaluga Region), the Vologda Region, and at the Department of Parasitology and Veterinary and Sanitary Expertise of the Moscow State Academy of Veterinary Medicine and Biotechnology – K. I. Skryabin MVA. We studied feces collected from bison of different sex and age groups near feeders in the runs, and in reserves, nurseries and in the wild. A total of 320 samples were collected and examined including 237 samples from the Prioksko-Terrasny Nature Biosphere Reserve, 15 samples from the Bison Nursery, 18 samples from the Bryansk Forest Nature Reserve, 29 samples from the Ugra National Park and 21 samples from wild bison from the Vologda Region. For helminth-coprological studies, we collected fresh feces of bison from the soil surface. The feces were examined according to generally accepted methods. The sequential washing technique was used to diagnose trematodiases, and the Kotelnikov-Khrenov and Fulleborn flotation methods were used to diagnose cestodoses, nematodoses and eimerioses.Results and discussion. The endoparasite fauna of the European bison was most diverse in the Prioksko-Terrasny Nature Biosphere Reserve, where we identified the parasitizing of two species of trematodes, one genus of cestodes, one species and four genera of nematodes and one genus of protozoa. All these pathogens parasitize both as mono- and mixed infections. One species of trematodes, one genus of nematodes and one genus of protozoa have been identified in the Ugra National Park. One genus and two genera of nematodes were found in the Bison Nursery of the Siberian Branch of the Russian Academy of Sciences of the Altai Republic and in the Bryansk Forest Nature Reserve, respectively. The dominant were gastrointestinal strongylatoses.

Searching for antiparasitics with a different mode of action than existing drugs, and (or) with the same but much more effective mechanisms is necessary to periodically update the applicable protection chemicals. For the first time we here present data on the biocidal action of new semisynthetic derivatives of avermectin B1 that we have synthetized earlier. These are the 16-membered macrocyclic lactones, the representatives of an important class of anthelmintics. In 2015 S. Omura (Japan) and W. Campbell (USA) who discovered this avermectin group, were awarded the Nobel Prize in physiology and medicine. In our study the oligochaetes Tubificidal tubifex were used as a test-object. The original chemicals and synthetized derivatives tested were avermectin B1 (abamectin), ivermectin, monosaccharide analogues of abamectin and ivermectin, namely abamectin, ivermectin, 5-O-succinyl avermectin B1, methyl ester of 5-O-succinyl avermectin B1, ethyl ester of 5-O-succinyl avermectin B1, diethyl ester of 5,4-di-O-succinyl avermectin B1, ethyl ester of 5-Omalonyl avermectin B1, diethyl ester of 5,4-di-O-dimalonyl avermectin B1, monosaccharide hemisuccinate of avermectin B1 (5-O-succinyl-4´-dezoleandrozyl-4´-hydroxyavermectin B1), ethyl ester of 5-O-succinyl-4-O-chloroacetyl avermectin B1, 5-O-succinyl ivermectin, ethyl ester of 5-O-succinoyl ivermectin, 5,4-di-O-succinyl ivermectin, diethyl ester of 5,4-di-O-succinyl-ivermectin, ethyl ester of 5-O-malonylivermectin, diethyl ester of 5,4-di-O-dimalonyl ivermectin, monoavermectin-5-yl ester of 4-[2-(4-nitrophenyl)-2-oxoethoxy]-4-oxobutanoic acid, monoavermectin-5-yl ester of 4-[2-(4-chlorophenyl)-2-oxoethoxy]-4-oxobutanoic acid, monoavermectin-5-yl ester of 4-[(4-nitrophenyl)-methoxy]-butanoic acid, monoavermectin-5-yl ester of 4-[1-methyl-2-(4-methylphenyl)-2-oxoethoxy]-4-oxobutanoic acid, monoavermectin-5-yl ester of 4-[2-(4-chlorophenyl)-1-methyl-2oxoethoxy]-4-oxobutanoic acid, monoavermectin-5-yl ester of 4-[3-chloro-1-(4-сhlorbenzoil)-propoxy]-4-oxobutanoic acid, monoavermectin-5-yl ester of 4-{2-[(4-methylphenyl)-amino]-2-oxoeth-oxy}-4-oxobutanoic acid and monoavermectin-5-yl ester of 4-{2-[(4-bromophenyl)-amino]-2-oxo-ethoxy}-4-oxobutanoic acid. The acute toxicity (LD 50 ) of the most effective ones, 5-O-succinyl avermectin B1, 5-O-ethylsuccinyl avermectin B1 and 5,4-di-О-ethylsuccinyl avermectin B1, for intraperitoneally challenged white mice was 37.85; 41.37 and 45.82 mg/kg, respectively. We also used membrane preparations of rat brain as in vitro model for screening and studying activity of natural and semi-synthetic avermectins. A radioligand [G-3H]SR 95531 binding assay of avermectin B1, ivermectin, and 5-O-succinyl avermectin B1 interaction with GABA-receptors (the biotargets for these compounds) showed a 30 % increase of maximal inhibition (Imax) of specific binding by hemisuccinate derivative of avermectin B1 when compared to original avermectin B1.

The purpose of the research is studying seasonal dynamics of gastrointestinal strongylatosis in bison in the Central Region of the Russian Federation.Materials and methods. The bison of different age and sex was studied in the Prioksko-Terrasny Nature Reserve, the Moscow Region. Fresh feces collected near feed troughs in enclosures in different seasons for three years were examined according to generally accepted methods. To analyze the infection rate of gastrointestinal strongylates in the European bison by months throughout the year, we took average monthly temperature and humidity values for 2018, 2019, and 2020 into account.Results and discussion. The maximum number of positive samples was diagnosed in the warm season of the year, namely, in summer and in the first months of autumn: August, September and October 2018 (79.3, 83.3 and 82.9%), August, October, November and December 2019 (73.7, 76.9, 77.1 and 77.8%), and June, July, August and October 2020 (85.6, 87.2, 88.0 and 86.3%). Ambient temperatures and precipitations affect significantly on the time of larvae development in the environment, which can be clearly seen in 2019.

The species composition of helminths of the class Trematoda Rudolphi, 1808 was studied in sheep of the Karachay rough-haired breed in Kabardino-Balkaria, which is represented by 7 types of helminths: Fasciola hepatica, Dicrocoelium lanceatum, Paramphistomum cervi, P. ichikawai, Liorchis scotiae, Calicophorum calicophorum, Eurytrema pancreaticum. These species met with an extensive invasion, respectively 16,67 %, 40,00 %, 20,00 %, 16,67 %, 13,33 %, 20,00 % and 6.67 % and the intensity of the invasion from 8 to 312 copies / head.

The article provides information about the commodity and technological properties of fresh-dry skins obtained from silver foxes infested with the nematode Toxascaris leonina, when added to the feed of the therapeutic and preventive complex DLK. Changes in the composition of the microflora of the gastrointestinal tract were shown in helminthiasis, and a violation of the formation of hair in young silver foxes was found, which further leads to a deterioration in the quality of freshdry skin. The addition of a sulfur-containing complex to the feed mixture allows infested animals to recover their hair faster, improve their product and technological properties, and improve the quality of fresh – dry silver Fox skins of cellular breeding