The article presents the results of studying the dynamics of the formation of antibodies and immune complexes, reveals the prospects for improving the early diagnosis of cattle leukaemia. Studies were conducted for 6 months on an experimental group of animals consisting of 12 cows. The titers of free and bound antibodies in blood serum and milk were determined by enzyme-linked immunosorbent assay. The results of studies showing that changes in titers of anti-leukaemia antibodies in the blood serum of cows naturally infected with BLV (bovine leukaemia virus) are significantly different from experimental infection data are adduced. In cows infected with BLV, there is no definite relationship between antibody titers in milk and in blood serum.  With sufficiently high titers of serum antibodies, antibody titers in milk can be minimal for the same cows; conversely, with low titers of serum antibodies, there can be high antibody titers in milk.  In the titers of antibodies free and bound in the immune complexes in blood serum with the development of the disease, a certain dependence is traced. With a decrease in titers of free antibodies, in most cases, an increase in titers of “bound” antibodies is observed, i.e., the degree of formation of circulating immune complexes (CECs) increases. There is no clearly defined dependence in the dynamics of changes in titers free and bound in immune complexes of antibodies in milk samples. They can remain at the same level for a long time, both at low and rather high levels.

Dairy farming is striving to achieve positive results both in milk production increase and quality improvement. Unfortunately, the conventional breeding selection system does not consider the genotypic identity that reflects the level and direction of the processes occurring in the organism. The modern breeding selection is based on the selection by a set of features. In breeding, those animals that have more valuable characteristics are considered valuable. Animal husbandry can achieve great success only when analyzing the biology of the animal body and productivity. In order to increase the genetic potential of cows in Russia, it is necessary to take into account genetics and milk productivity. Analysis of milk productivity of cows with different LTF genotype in their pedigrees showed that the maximum milk yield was in cows of the Ayvengo line with the LTFAB genotype. These cows were distinguished from other cows by their high protein content, and these animals had the lactoferrin gene. And the animals of the Ayvengo line differed in the level of fat in milk. The comparative PCR-RFLP analysis of the blood DNA samples of the first-calf Holstein cows showed the benefit virtually by all milk production indicators (milk yield, milk protein and fat), including by somatic cell content in milk of the Ayvengo and Sovereign line cows with the LTFAB genotype. The Aydial line stock with the LTFAB genotype is worthy of notice regarding the selection activity.

Scientific studies of feeding dairy cattle prove that it is most rational to balance rations according to standardized nutrition indicators due to concentrates, which contain all the necessary nutrients in the main diet, consisting of bulky feed (succulent and rough). The advantage of using protein supplements in the feeding of farm animals is that there is no need for oncoming transport of grain fodder and animal feed, which significantly reduces the cost of livestock production.  The digestive apparatus of ruminants, due to the presence of pre-stomachs, is adapted to the absorption and digestion of a large number of coarse plant foods. The main feature of the processes of digestion of ruminants is that the food eaten by animals is exposed to microorganisms in the rumen. Ammonium and other nitrogenous compounds are an accessible form of nitrogen for organisms from which a microbial protein is synthesized in a rumen. This protein and unsplit protein feed are sources of coverage of the amino acid needs of the animal. In this regard, the aim of this work was to study the metabolic processes in the rumen of ruminants. To study the effect of the carbohydrate-vitamin-mineral concentrate «LS», 2 groups of animals were formed with 8 animals each. The contents were investigated: pH, the total concentration of volatile fatty acids (VFA) - butyric, propionic and acetic; the total number of microorganisms and number of ciliates. The introduction of the carbohydrate-vitamin-mineral concentrate «LS» in the diets of dairy cows for 30 days contributed to an increase in the name of bacteria by 3.3±3.4% and protozoa by 6.7±4.1%. In the cicatricialcontent of the experimental groups, the number of volatile fatty acids increased by 12.4±2.4% and propionic and butyric acids by 3.4±3.1 and 5.7±2.7% in relation to the control group of cows

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