Parainfluenza virus-3 is the most common etiological agent in mixed respiratory diseases of calves with high concentrations of animals. The more severe course of the disease is observed with complications from bacterial or other viral infections. This article presents the results of clinical and epizootic, serological, virological and molecular genetic studies. A cytopathogenic agent was isolated from a pathological material taken from patients with respiratory diseases of calves in a BEK cell culture. Based on the results of serological and molecular biological studies, this isolate ("LD-9") was identified as the parainfluenza-3 virus in cattle.

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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.

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Учредитель и издатель: Founder and editor: ФГБОУ ВО «Казанская государственная академия ветеринарной медицины имени Н.Э. Баумана» (ФГБОУ ВО Казанская ГАВМ) FSBEI HE «Kazan Bauman State Academy of Veterinary Medicine»(FSBEI HE KSAVM) Печатается по решению редакционной коллегии Казанской государственной академии ветеринарной медицины им. Н.Э. Баумана от 5 Июня 2018 г