Purpose: to study polymorphism in the PRPN gene in sheep of the Southern Meat breed and determine their genetic resistance to the classical and atypical scrapie.
Materials and methods. The biomaterial was ear plucks from 442 sheep of the gene pool herd of the Southern Meat breed, selected from the Ladozhsky Breeding Plant. Sheep genotypes associated with scrapie resistance were determined based on sequencing of a fragment of the ovine PRNP gene. Sanger sequencing of the sheep PRNP gene fragment was carried out on a Nanofor 05 genetic analyzer, according to the methodological recommendations by T.E. Deniskova et al. Sequencing data were processed using the Mutation Surveyor V5.1.2 program (Release), and allele polymorphism in codons 136 (A/T/V), 141 (L/F), 154 (R/H) and 171 (Q/R/ H/K) were determined based on the analysis of the obtained sequences. Statistical data processing was carried out using Microsoft Excel and GenAlEx 6.501.
Results. Analysis of PRPN gene polymorphism showed the presence of seven alleles (ARR, ARQ, AHQ, ARH, AHH, AHR, and VRQ) in the studied sample. The desired haplotype ARR was found in all sheep groups, the frequency across the sample was 21,43 %. It`s minimum frequency was 18,18 % in the group of ewes, and the maximum was 23,08 % in the group of young ewes. The undesirable allele VRQ, associated with sensitivity to the classical scrapie, was not detected in the group of rams (sires) in the studied sample. In the remaining groups, this allele varied from 7,14 % in young rams to 9,09 % in ewes, and the frequency in the entire sample was 6,12 %. In this study, we discovered a new rare haplotype AHH, which was not previously reported either in the Southern Meat or in other sheep breeds. The AHH allele was present in all studied groups of the Southern Meat sheep breed with frequency varied from 7,69 % in young ewes to 13,64 % in ewes. The analysis of the frequency of genotypes in the studied sample of sheep of the Southern Meat breed, sixteen genotypes were identified (ARR/ARR, ARR/AHQ, ARR/ARH, ARR/ARQ, ARQ/ARQ, ARQ/AHQ, ARQ/ARH, ARQ/AHH, ARH /ARH, ARH/AHH, AHQ/AHQ, AHH/AHH, AHR/AHR, ARR/VRQ, ARQ/VRQ, VRQ/VRQ), corresponded to five classes of genetic resistance to scrapie. The frequencies of the desired genotypes varied widely among different age groups of sheep. The F allele at codon 141, associated with genetic susceptibility to the Nor98 strain, was not detected in any individual in the studied sample. We recommend analyzing the polymorphism of the PRPN gene for susceptibility to classical and atypical scrapie as an additional selection criterion for effective breeding work. This procedure will significantly increase the genetic resistance to scrapie in new generations of sheep of the Southern Meat breed.

Purpose: Chimeric birds are of interest in breeding and genetic engineering. Identification of such birds was initially phenotypic, for which breeds with contrasting plumage color were used. However, this method is imperfect, and the purpose of this work was to develop an optimal method for identifying interbreed chimeras of birds. Materials and methods. Based on the Central Clinical Hospital of the Breeding Community "Genetic Collection of Rare and Endangered Chicken Breeds of the All-Russian Research Institute of Chicken Breeding and Geography of the Russian Academy of Sciences", 4 breeds were selected: Poltava Clay, Sussex, Pale Brahma, and Light Brahma as donors and recipients. These breeds were selected based on genetic differences: Pale Brahma and Poltava Clay have the s+ allele of the Silver gene, Light Brahma and Sussex have the S allele of the same gene. The difference between the two alleles is ensured by a single nucleotide substitution C\T, which significantly simplifies identification. Chimeras were obtained by transplanting donor cells into recipient embryos. Among the obtained birds, some demonstrated a mosaic phenotype with the manifestation of the donor breed traits, while others had the phenotype of the recipient breed. After slaughtering the birds, tissue samples were taken from the ovaries, testes and liver. DNA was isolated from them using the standard phenol-detergent method. DNA samples were examined by amplification using allele-specific probes at the SLC45A2 (Silver) gene locus located on the Z chromosome (alleles S and s+).
The genotyping results showed that among the analyzed DNA samples from 12 experimental birds, 5 were found to have both donor and recipient genotypes. At the same time, in 4 chimeras, the donor genotype was detected in the reproductive organs, i.e. these chimeras are sexual and could pass on the donor genotype to their offspring.

Mountain cattle and Caucasian Brown breed bred on the territory of the Republic of Dagestan are valuable genetic resources due to their adaptive abilities. The analysis of genetic diversity using STR- and SNP-markers made it possible to estimate allelic diversity and the level of heterozygosity, as well as to study the population structure of these breeds and the relationship with other breeds. Analysis of genetic diversity by STR- and SNP-markers revealed a significant lack of heterozygotes in Mountain cattle (0,057 and 0,020). The highest allelic diversity in STR markers was detected in Mountain cattle (9,241), for SNP – in the Caucasian type of Brown Swiss breed (1,991). Principal component analysis (PCA) was performed to assess interbreed relationships. The PCA analysis by STR markers showed that Mountain cattle and Caucasian Brown breed form relatively independent clusters overlapping with the Brown Swiss breed. The PCA analysis by SNP markers allowed a clearer separation of the populations. Analysis of the structure of the genetic network by STR- and SNP-markers showed a common origin between Mountain cattle and the Caucasian type of Brown Swiss. Cluster analysis of the studied populations was carried out with the number of clusters ranging from 2 to 5. The optimal number of clusters is 4. According to STR-markers at K = 2, the Mountain cattle differentiated from other studied groups. At K= 3, the Caucasian Brown breed is distinguished to a separate cluster. When the number of clusters increases up to five, there is a division into two subgroups within the Mountain cattle. According to SNP-markers, at K= 2, the Brown Swiss is separated from other investigated groups. When the number of clusters increases up to five, two subgroups with different genetic components are distinguished in the Caucasian brown breed. 

The aim of the study: Investigation of the polymorphism of the DMRT3 gene (сhr23:22999655 C>A) associated with the racing performance in Orlov Trotters.
Materials and methods. A group of 69 purebred Orlov Trotters born in 2013, 2014 and 2015 was tested for SNP C>A (chr23:22999655) using PCR-RFLP method and their racing career was analyzed. All the tested animals were sired by one the same stallion. The analysis of the racing performance of trotters in the experimental group included the number of starts for each horse, the number of wins, the best racing time at a distance of 1600 m, correctness of the trotting gait and occurrence/absence of breaks.
Results. It was found that Orlov Trotters that had the heterozygous A/C genotype were generally superior to horses with the C/C and A/A genotypes, both in the best racing time and in the number of starts and wins. In the study, breaks and cases of incorrect trotting gait were recorded in 19 trotters with the heterozygous A/C genotype, 7 trotters with the homozygous A/A genotype and 3 trotters with the homozygous C/C genotype. Interestingly, in the group of horses with the A/A genotype 6 trotters out of 9 had the registered incorrect trotting gait, which meant pacing or any other disorders in the synchronous diagonal movement of the limbs.
Conclusion. The study demonstrated that Orlov Trotters with the A/C genotype are better racers then horses with the C/C and A/A genotypes.

Purpose: to summarize the results of scientific publications on the use of genome-wide associative studies of economically important traits in rainbow trout (Oncorhynchus mykiss).
Materials and methods. PubMed Scientometric Database (https://pubmed.ncbi.nlm.nih.gov /), Science Direct (https://www.sciencedirect.com /), scientific electronic library eLibrary (https://elibrary.ru /).
Results. An important step in improving breeding programs for rainbow trout (Oncorhynchus mykiss) is the use of knowledge about the genetic architecture underlying the variability of economically useful traits. In 2014, the first version of the reference genome assembly was published, which served as the basis for the identification of single-nucleotide polymorphisms and the development of a medium-density DNA chip, which, in turn, made it possible to conduct genome-wide association studies (GWAS). GWAS makes it possible to identify SNPs with great effect responsible for phenotypic variants that can be given priority in genomic selection, which will make it possible to carry out further intra-family selection based on the most economically important characteristics. Many scientific papers have been devoted to the use of genome-wide associative research in trout farming. The review shows the relevance and prospects of using the GWAS method in aquaculture breeding of rainbow trout as a tool for identifying candidate genes that affect growth, meat quality and disease resistance. Having analyzed the foreign experience of using GWAS, I would like to note its relevance and prospects, because most of the economically useful features are polygenic in nature.

Purpose: Development a system for identifying alleles of the BoLA-DRB3.2 locus aimed at amplifying short target fragments with subsequent Sanger sequencing, suitable for studying samples containing damaged DNA.
Materials and methods. For the first time, a test system for sequencing the polymorphic region of the BoLA-DRB3 gene according to Sanger was developed, suitable for analyzing degraded DNA. The system was tested on 10 modern and 4 ancient cattle samples. Sequence alignment and allele typing were performed using the UGENE v1.32.0 program and the BLAST online resource.
Results. A test system was developed that allows amplifying a fragment of the BoLA-DRB3.2 locus suitable for further analysis using Sanger sequencing and allele typing. Four DNA samples obtained from ancient samples provided by the Institute of Archaeology of the Russian Academy of Sciences were analyzed. A total of 13 samples of modern cattle of different breeds were used as a comparison group. For all studied samples, it was possible to obtain sequences of a highly polymorphic fragment of the second exon of the BoLA-DRB3.2 locus, 114 bp long, located at BTA23:25730221-25730334 (ARS-UCD2.0 assembly, GenBank: GCF_002263795.3). However, some nucleotides were identified ambiguously during sequencing for some samples. It was possible to confidently type alleles for 10 out of 13 samples: the identity of the analyzed sequences with the reference allele sequences was more than 99 %. Three modern samples were identified with a lower identity level (95,536, 96,429 and 98,214 %, respectively, for MOD1, MOD9 and MOD8), which may be due to inaccurate reading of the nucleotide during sequencing.

Purpose: molecular genetic testing of purebred bulls of the Belgian blue, Charolais and Aberdeen Angus breeds and determination of the frequency of occurrence of genotypes and alleles by the genes of calpain, myostatin and thyroglobulin.
Materials and methods. For the experiment, biological material (sperm) of purebred bulls of the blue Belgian, Charolais and Aberdeen Angus breeds was used. DNA genotyping of bulls by the genes of calpain (CAPN1), myostatin (MSDN) and thyroglobulin (TG5) was performed using the polymerase chain reaction (PCR) method and polymorphism of the lengths of the extraction fragments (PDRF). Nuclear DNA was isolated by the perchlorate method. The solution for DNA isolation was prepared according to T.Maniatis et al.[11], and solutions manufactured by ODO "Primtech" Republic of Belarus were used for amplification and restriction. 
Results. Having studied the genetic structure of purebred bulls of the blue Belgian, Charolais and Aberdeen Angus breeds, it was found that animals of all breeds are monomorphic to MSTN (100 %) according to the MSTN gene. According to the calpain gene (CAPN1), polymorphism was established in blue Belgian bulls and homozygous CAPN1GG genotype (50 %) and heterozygous CAPN1AG (50 %) were identified, homozygous CAPN1GG genotype (25 %) and heterozygous CAPN1AG (75 %) were identified in individuals of the Aberdeen Angus breed. According to the TG5 gene, the producing bulls of the blue Belgian breed are monomorphic TGCC (100 %). The bulls of the Charolais and Aberdeen Angus breeds have a thyroglobulin gene polymorphism: the Charolais breed has homozygous TG5CC (50 %) and heterozygous TG5TC (50 %), and the Aberdeen Angus bulls have heterozygous TG5TC (50 %) and two homozygous TG5TT (25 %) and TG5CC (25 %).
Conclusions. The genetic structure of purebred blue Belgian, Charolais and Aberdeen Angus bulls based on the genes of calpain, myostatin and thyroglobulin. The genetic structure of purebred stud bulls of the Blue Belgian, Charolais and Aberdeen Angus breeds indicates that animals of all breeds are monomorphic according to the MSTN gene. In bulls of the blue Belgian breed, polymorphism was established and the homozygous genotype CAPN1GG (50%) and heterozygous CAPN1AG (50 %) were identified, and in individuals of the Aberdeen Angus breed, the homozygous genotype CAPN1GG (25 %) and heterozygous CAPN1AG (75 %) were identified. In Charolais breeding bulls, polymorphism was established for the TG5 gene and the homozygous genotype TG5CC (50%) and heterozygous genotype TG5TC (50 %) were identified.

Along with the pedigrees and productivity of animals, the evaluation of linear conformation traits (such as rib structure, rump angle, legs set and udder depth) is an important task in assessing the estimated breeding value of dairy cattle. Despite the existing international standard of the International Committee for Animal Recording (ICAR), which regulates the study of the cattle exterior, different countries still use their own significantly varying lists of linear traits and characteristics. This leads to a potential difficulty in animal comparison, for example, when selecting calves for purchase. In particular, the analysis of linear conformation traits from 14 countries showed that only 50 % of the main ICAR traits were simultaneously present in all lists. A similar analysis for Russia also revealed the presence of varying conformation traits in different regions. Although the Russian lists turned out to be more homogeneous than the international ones, they still differed from the ICAR, including only 77 % of the main linear traits at the same time.
The further development of domestic breeding and the process of data unification can be facilitated by expanding ICAR conformation traits list. The proposed expanded list takes into account the already accumulated traits from Russian regions aas well as ICAR linear traits in order to increase the gathered data volume. As a result, it is expected to collect a total of 29 linear conformation traits, which will enable the best dairy cattle description and will improve the accuracy of calculations of the Russian animals breeding index.

Purpose: to analyze the productive qualities of the leading families of Holstein cattle of the SPK PZ «Detskoselsky» of the Leningrad region.
Materials and methods. The object of research was black-and-white Holstein cows in the amount of 1,425 heads. In order to ensure the representativeness of the data, animals belonging to a family consisting of at least 15 cows were selected from the entire livestock, the best families were selected according to milk productivity (milk yield, fat content in milk). Thus, the sample consisted of 456 cows belonging to 17 families. The research material was the cards of breeding cows (F2-MOL), data from the breeding and primary zootechnical accounting of the IAS "Selex" SPK PZ "Detskoselsky" in the period from 2021 to 2023. The calculation of breeding and genetic parameters was carried out according to standard methods (N.A. Plokhinsky, 1970, E.K. Merkuryeva 1970) using modern computer technology using the MS EXCEL analysis package.
Results. As a result of the analysis of milk productivity for the first and last completed lactation of cows belonging to the leading families, the best milk productivity indicators were revealed (milk yield, fat and protein content in %, milk fat and protein yield in kg). The selection and genetic parameters characterizing the dairy productivity of cows of the leading families are calculated.
Conclusion. The selection and breeding work carried out with families in the conditions of the SPK PZ «Detskoselsky» has positive results. In order to further improve the breeding and productive qualities of animals, it is necessary, along with line breeding, to continue working with families, intensively use the most productive ones for offspring – Ag'e 16, Barka 34, Bozhayu 28, Bravaya 49, Vervahting 61, Viktoriya 67, Gulena/Gulla 78/171, Lyura 134/136, Majka 150 and Teres 221 and also create new even more productive families.

Purpose: Development of approaches to improve breeding work and management of genetic resources of domestic reindeer. 
Materials and Methods. The research was conducted on domestic reindeer of the Even breed raised at the "Yuchugeiskoe" farm. To accomplish this work, calf weighing, collection of genetic material, tagging, assignment of calves to their mothers, genetic passportization, assessment of calves by body weight, and evaluations of breeding reindeer based on offspring quality were performed. Genotyping and paternity testing were carried out using multiplex PCR analysis of 16 microsatellite loci recommended by the International Society for Animal Genetics (ISAG).
Results. The article presents the results of an assessment of domestic reindeer based on the quality of their offspring. During the study, calves were weighed and assigned to their respective mothers. The breeding value of the current year's calves was assessed. The application of molecular-genetic methods in domestic reindeer husbandry allowed solving issues related to paternity determination. This article will be of interest to professionals in the field of reindeer farming. Results comparing the productivity of offspring with that of their peers and the average herd performance are presented. A comparative evaluation of producers based on the body weight of their six-month-old offspring revealed significant variations in body weight among different producers. The study highlights the importance of utilizing modern methods to evaluate offspring quality and enhance breeds of domestic northern reindeer.

The effectiveness of using a number of methodological documents regulating the assessment of body type in improving domestic dairy cattle, adopted in 1996, 2019 and 2023, respectively, was studied. The materials of the conducted studies convincingly indicate that the "Assessment of cows by exterior features" approved as a normative legal act (decision of the EEC board dated 08/22/2023 No. 125) will not allow a full and reliable assessment of the breeding stock by their body type and, accordingly, the effective use of the obtained data in the selection of dairy cattle. "Rules for assessing the body type of daughters of dairy and meat breed bulls" (1996) are intended to assess cows of combined (dairy and meat) productivity and therefore their use in the selection of dairy cattle is not effective enough. At present, it is advisable to use the "Methodology for assessing the constitution of cows in dairy cattle breeding" (2019) in the work on improving the exterior of dairy cattle productivity, which is identical to the "Evaluation of cows by the exterior characteristics of cows" (2023) in terms of the linear system of certification of the constitution type, but also additionally contains all the requirements and sections necessary for successful work. This methodological document has been used for five years in the assessment, selection and selection of breeding animals in farms in the Vladimir, Moscow and Ryazan regions and has proven itself from the best side. At the same time, this methodology is fundamental in the selection of cows for participation and determining the winners in the "Best Cow by Constitution Type" competition, held as part of annual exhibitions of breeding animals in a number of regions of the Russian Federation.

The aim of this study was to evaluate the impact of the frequency of electrofusion on the efficiency of sheep cloning and to assess the dependence of this effect on the duration of serum starvation of somatic cells (SC).
Materials and Methods. Fetal fibroblasts at passages IV-V were used as donor cells for somatic cloning. To arrest the SCs in the G0/G1 phase of the cell cycle, after reaching near-confluence (approximately 90%), the cells were subjected to serum starvation (SS) for 24 and 48 hours. Recipient oocytes were collected from post-mortem sheep ovaries, matured in vitro, and reconstructed through enucleation followed by the transfer of SC into their perivitelline space. Electrofusion was used to combine the oocyte/SC complexes. The oocyte/SC complexes were fused using electrofusion in a buffer containing 270 mM mannitol, which involved the application of two sequential direct current pulses at 40 V for 20 µs. Complexes that did not fuse after the first treatment were subjected to a second round of electrofusion. The obtained cytohybrids were activated using ionomycin, followed by a 4-hour incubation in the presence of 6-dimethylaminopurine and cycloheximide, and subsequently cultured for 48 hours to assess embryonic development.
Results. In this study, a total of 504 oocytes were reconstructed. A statistically significant higher number of cleaved cytohybrids was observed from the first fusion when fetal fibroblasts subjected to 48-hour SS were used as karyoplasts. The number of embryos obtained from the second fusion was not dependent on the duration of SS in SCs. When SCs subjected to 48-hour SS were used, statistically significant differences were found between the proportion of cleaved cytohybrids from the first and second fusions: 62,2±21,48 % and 31,4±26,43%, respectively (p=0?010). The proportion of cleaved cytohybrids obtained from the second fusion was 35,2 % and 28,6 % of the total number of cloned embryos for 24-hour and 48-hour SS, respectively, which significantly contributed to the total number of early-stage embryos. The results presented in this article should be considered preliminary, as further research is necessary to obtain embryos at later developmental stages and to assess their quality.

Purpose: a morphological study of the liver of white laboratory rats of the Wistar line supplemented with the mineral feed additive based on chelate compounds.
Materials and methods. The experiment was carried out on male white Wistar laboratory rats weighing 200-250 g. “Chelavit C” was used as a mineral feed additive. After three months, the animals were euthanized using inhaled drugs combined with an injection overdose of anesthetic. Morphological analysis was performed on macro- and micropreparations of the liver. For a general assessment of the histological organization of the liver, hematoxylin-eosin staining was used. Iron accumulation in the liver was assessed using Perls Prussian blue stain.
Results. The differences in some essential clinical and morphological parameters assessed on macroscopic specimens of the liver of animals from the experimental and control groups were insignificant, being within the acceptable physical and anatomical norm. Morphometric analysis performed on histological preparations of the liver did not reveal differences between the groups, and the parameters were within acceptable standards. The Perls Prussian blue stain showed that the iron content in the liver of animals in the experimental and control groups corresponds to normal values (from 1+ to 3+); therefore, the feed additive based on chelate compounds does not cause hemosiderosis, which can later develop into hemochromatosis.
Conclusion. The mineral feed additive based on chelate compounds replenishes lost microelements without having a toxic effect on the liver of rats. However, when administering this additive to animals, it is necessary to accurately calculate the dosage to avoid possible toxic effects

Purpose: to study the development of morphophysiological blood parameters (status) in purebred Tashla sheep raised in an industrial complex, as well as depending on the age and functional state of the mothers who gave birth to them.
Materials and methods. The experiment involved 8 Tashla ewes of the first lambing and 8 lambs obtained from them, as well as 8 Tashla ewes of the third lambing and 8 lambs obtained from them. For the studies, blood samples were collected from 16 lambs and 16 ewes in dynamics at the following time intervals corresponding to the age from birth of the lambs: 30, 60 and 90 days from birth for lambs, and 90 days after birth for ewes, which corresponded to a certain physiological development of the lambs and the functional state of the ewes. The blood of the animals was collected by jet blood flow into test tubes with EDTA. For the study of morphophysiological parameters, the blood was cooled to +4 °C. Blood samples from lambs and sheep were tested for the following parameters: WBC (white blood cells, the main immune cells), RBC (red blood cells, responsible for oxygen transport), HGB (hemoglobin, the main protein component of red blood cells), HCT (hematocrit, or the percentage of red blood cell volume to the total blood volume), MCV (mean corpuscular volume), MCH (mean corpuscular hemoglobin content), MCHC (mean corpuscular hemoglobin concentration), RDW (red blood cell distribution width, an indicator of red blood cell heterogeneity by volume, characterizes the degree of anisocytosis), PLT (platelets, blood elements responsible for the formation of a thrombotic clot during bleeding), MPV (mean corpuscular volume), PDW (red blood cell distribution width, an indicator of platelet heterogeneity, shows which cell forms predominate), PCT (platelet crit, reflects percentage of platelets in whole blood).
Results. The results obtained showed that in Tashla lambs during the suckling period, the morphophysiological picture of the blood is actively developing. Certain patterns of age-related changes in the morphophysiological parameters of the blood of lambs with age, as well as some features of those in sheep of different functional states (sheep of the first and third lambing) were revealed. A qualitative difference in the parameters in animals of the same age, but different functional states, is noted for the MCV, MCH, RDW, MPV, PDW, PCT, and only in adults. Reliable differences in changes in the morphophysiological parameters of the blood are observed in lambs with age. The morphophysiological parameters of the blood of Tashla sheep play a special role and are of key importance in the process of assessing the physiological status of their body, and also demonstrate that its formation occurs in the period from the 60th to the 90th day after birth. 

Purpose: to study the indices of mineral metabolism and vitamin D level in blood of calves and to identify their interrelations.
Materials and methods. To achieve the set objective, blood was taken from the jugular vein of 15 calves aged from 8 to 15 days. Blood serum was analyzed for calcium, inorganic phosphate, magnesium, and alkaline phosphatase activity using standard biochemical test systems and a semiautomatic analyzer CLIMA MC-15. The study of 25-hydroxycalciferol in blood serum was carried out by the enzyme immunoassay method using the test system "25-OH vitamin D-IMAXYZ (IMAXYZ)" and a vertical scanning microplate photometer MULTISCAN.
Results. A different degree of scatter of results was revealed. The highest degree of homogeneity was determined for the calcium level in the blood of calves (CV = 7,57 %). The variation coefficient for the concentration of inorganic phosphorus, magnesium and the calcium to phosphorus ratio is determined within 12,08—16,29 %. The most pronounced heterogeneity in the sample is determined for the alkaline phosphatase (CV = 25,85 %) and 25-hydroxycalciferol (CV = 31,85 %) indicators, in the variation series of which the highest and lowest values differ by more than 2,5 times. Calculation of the Pearson coefficient made it possible to identify the closest relationships between the content of 25-hydroxycalciferol and inorganic phosphate in the blood (r = -0,74) and the Ca / P ratio (r = 0,71). To a lesser extent, the alkaline phosphatase activity (r = -0,61) and the calcium level (r = 0,41) are interconnected with the level of 25-hydroxyvitamin D. Virtually no correlation was found between vitamin D and the concentration of magnesium in the blood.
Conclusion. In calves aged 8 to 15 days, a large spread in the range of alkaline phosphatase activity and 25-hydroxycalciferol content in the blood is determined with a relative homeostatic constancy of the calcium level. The Ca/P indica tor has the closest positive relationship with the 25-hydroxycalciferol level, and the alkaline phosphatase activity shows the closest negative relationship with this indicator, which seems quite logical: insufficient bone mineralization in a growing organism is associated with an increase in the induction of this enzyme. No relationship was determined between the concentration of 25-hydroxycalciferol and magnesium. The data obtained indicate a different state of mineral metabolism in calves in the early postnatal period of life and the need for careful monitoring of metabolism for timely correction of vitamin and mineral deficiency in the diet of growing calves.

The study of biochemical blood parameters in caged foxes plays an important role in ensuring their health and preventing diseases. Blood components within physiological limits can change their balance during disease, making the blood biochemical profile a key tool in diagnosis. The body's enzyme system primarily responds to changes in environmental conditions, even in the absence of obvious clinical signs. The main metabolic indicators were studied (using “High Technology” (USA) reagent kits): total protein, albumin, alanine aminotransyaerase (AlAT), aspartate aminotransferase (AsAT), urea, creatinine, cholesterol, α-amylase. It was established that these analytes in crossbred foxes of the red marbled color type were within the generally accepted limits of the physiological norm for foxes. A study of the dynamics of AlAT (alanine aminotransferase) and AsAT (aspartate aminotransferase) levels in female and male foxes revealed general patterns in their changes during growth and development. A decrease in the level of analytes by 4 months of age and an increase by 6 months, indicating more intense metabolic processes in the body of foxes, especially on the eve of the winter period, which may be associated with the accumulation of body weight to maintain energy in the cold months. In females and males, there is a significant decrease in the level of alkaline phosphatase with age, reaching a decrease in females of 30 % (p≤0,05) by 4 months of age and 56,54 % (p≤0,05) by 6 months of age and in males by 33,06 % (p≤0,05) by 4 months and 51,76 % (p≤0,05) by 6 months, respectively, relative to the level noted in 1,5 month old puppies. In females, there was a relative decrease in total protein of 24,8 % (p≤0,05) between the ages of 1,5 and 4 months, and then an increase of 4,7 % by 6 months. Males also show a similar trend, with total protein levels decreasing by 38,9 % (p≤0,05) by 4 months, and then concentrations returning to levels at 1,5 months of age, with a difference of 6,6 %. Thus, the dynamics of changes in the studied analytes in female and male foxes indicates not only the physiological development of the organism during growth, but also highlights adaptive changes, which may be important for understanding their metabolic processes and general health.

Purpose: To identify subpopulations of T- lymphocytes in the bone marrow of lactating mice and newborn mice.

Materials and methods. The studies were carried out in lactating mice and newborn mice. 2 groups of 5 animals each were formed. For the experiment, bone marrow was collected from the animals from the proximal femur. The head of the femur was cut off and the bone marrow was removed using a syringe, which was used to wash the bone marrow cavity with saline solution. The phenotype of adaptive immune cells was determined using a set of fluorochrome-conjugated antibodies: CD4-PerCP-Cy5.5, CD8-PE/Cy7, CD62L-APC/Cy7, CD44-BV510. Data collection was carried out on a CytoFlex flow cytometer (Beckman Coulter, USA). The results were analyzed in the Kaluza Analysis 2.1 program.

Results. The study found that CD8⁺ T -cells of effector (T_EM; CD44⁺CD62L^-) and central memory (T_CM; CD44⁺CD62L⁺) are greater in adults, while the proportion of CD4⁺ T -cells of naïve memory (T_NV; CD44^-CD62L⁺ , predominates in pups. The content of the subpopulation of naive memory CD8⁺ T -cells (T_NV; CD44^-CD62L⁺) is 1,31 times higher in newborn pups and amounted to 81,97±2,38 % and 62,57±1,48 %, respectively. A significantly low content of populations of CD4⁺T - effector memory cells (T_EM; CD44⁺CD62L^-) in mice was established: 5,62±2,15 % compared to adults 13,26±1,93 % (p<0,05). ). Effector and central memory CD8⁺ T -cells (T_EM; T_CM;) enter the bone marrow in large numbers. This indicates that lymphocytes take an active part in the cellular mechanisms of the immune response. In the bone marrow, during immune reactions, numerous subpopulations of T -lymphocytes are formed and accumulate, in particular, cytotoxic cells and memory T -cells, which are directly responsible for adaptive immunity.

Purpose: to analyze physiological dependencies between the parameters of variational pulsometry in sport horses at relative rest to assess the possibility of including them in a comprehensive approach to analyzing the functional state of the body.
Materials and methods. The object of the study was 150 sport horses - Orlov trotter, Russian trotter, American trotter and Hanoverian breeds. The complex electrophysiological laboratory "CONAN" was used to record the ECG. The electrocardiogram was recorded in a standing position on a tether at the tie-up. Statistical analysis of the data was performed using the Statistica 10.0 program. Spearman's nonparametric method was used to analyze correlation relationships.
Results. The correlation physiological dependencies between the main parameters of variational pulsometry in sport horses were studied based on the mathematical analysis of the variability of the cardiac electrocardiogram according to the method of R.M. Baevsky. The specified parameters of variational pulsometry were studied in 150 horses of different sports orientations. Correlation relationships were estimated using Spearman's method. Variational pulsometry allows obtaining cardiac activity estimates that correlate significantly with each other.

The purpose of this work is to determine the effect of interleukins on the reproductive system of animals based on the analysis of the results of domestic and foreign scientific research. Currently, cytokines are considered as protein cellular mediators secreted by blood cells and performing the main function in the transmission of information. Interleukins are a group of cytokines that provide mediator interaction in the immune system and communicate with other body systems. It is known that the expression of cytokines can change as a result of the interaction of the producer cell with microorganisms, their fragments or secreted products of bacterial nature [1]. There are numerous data in the literature that confirm the similarity of the ovulation process with the inflammatory process. Analysis of the results of scientific studies devoted to the study of the importance of interleukins in the reproduction process indicate their key importance in the process of fertilization and fertility of the female body. However, the mechanism of action of this group of cytokines on the reproductive system of females has not been disclosed, which determines the relevance of this area.

Purpose: to study the efficiency of using a microelement-based bolus to improve feed digestibility in Simmental dairy cows in Yakutia.
Materials and methods. Three groups of animals were formed, each with three heads, based on the pair-analogue principle, taking into account age and live weight. Cows in the 1st experimental group received the feed additive "Calcitop Bolus" at a dose of 1 bolus per head once during lactation and the mineral premix "Dar Velesa". Cows in the 2nd experimental group received only the feed additive in the form of a bolus. The 3rd group was the control. During the entire scientific and economic experiment, in the stall period, the experimental animals of all groups received a balanced diet in accordance with the detailed feeding system. The bolus was administered to dairy cows using a special applicator. The analysis of feed, its residues and animal feces was studied using near infrared spectroscopy on a Spectra Star 2200. The digestibility coefficients of nutrient diets were calculated based on the ratio of the amount of digested nutrients to those consumed and expressed as a percentage. The nutritional value of the diets was determined based on the chemical composition and digestibility coefficients. 
Results. Feeding the feed additive in the form of a bolus to Simmental cows made it possible to balance the diets for missing nutritional elements and improved the palatability of the main feeds during the stall period. It ensured normal development and increased the digestibility of nutrients in the feed. Thus, the digestibility of nutrients was higher in the cows of the 1st experimental group, with a high level of digestibility compared to the control and 2nd experimental groups was established for dry matter by 3,2 and 0,7 %, organic matter by 1,2 and 0,5 %, crude protein by 1,4 and 0,5%, crude fat by 1,4 and 0,7 %, crude fiber by 1,9 and 0,4 % and NEF by 4,4 and 3,5 %. The digestibility coefficients of dry matter in cows of the 1st experimental group were higher by 1,41%, organic matter — by 1,14 %, crude protein by 5,25 %, crude fat by 0,82 %, crude fiber by 2,56 % and NEF by 0,43 % (p<0,95). Good absorption of calcium and phosphorus was noted in all groups.

Purpose: study of endobiont ciliates inhabiting forestomachs of Siberian roe deer living in the Republic of Sakha (Yakutia).
Materials and methods. Samples of the contents of all sections of the gastrointestinal tract were collected during post-mortem examination of carcasses of animals killed by hunters, the womb and internal organs. The samples were placed in sterilized 10 ml containers containing 10% formalin solution. Material from different sections of the gastrointestinal tract was examined microscopically in fixed smears-samples. Species affiliation, abundance and morphological parameters were determined.
Results. In the course of the work, two species of ciliates of the genus Entodinium were identified: Entodinium dubardi and Entodinium exiguum. It is noteworthy that E. exiguum is specific to roe deer and is not found in other herbivorous animals of the region, which may indicate its adaptation to the unique conditions of existence of this species. This discovery suggests the possibility of transmission of this microorganism to other animals through feces in pastures. The morphometric data of ciliates identified in the forestomachs of Siberian roe deer are as follows: the length of Entodinium dubardi is on average 36,3±2,4 μm, the width is 24,9±1,7 μm, while Entodinium exiguum has an average length of 40,4±2,51 μm and a width of 19,4±1,9 μm. The comparison showed that E. dubardi is common not only among roe deer, but also among local cattle, which indicates its versatility in the ecosystem. In addition, the studies revealed seasonal fluctuations in the number of ciliates in the forestomachs of roe deer: in summer, their number increases, while in winter there is a sharp decrease in their number, which can negatively affect the digestion process, since the similarity coefficient of individuals was KJ-M = -0.6, and the index of fauna community was about 50 %.