Bovine colostrum is a mammary gland secret which, due to its high immunoglobulin concentration, is necessary for the transfer of passive immunity to the calf, preventing diseases caused by microbial infections in the newborn ruminants. Colostrum, however, may contain pathogens and can be an infection transmitter, affecting morbidity and mortality rates of calves in the farms. Total plate count and immunoglobulin concentration are two main factors affecting colostrum quality, therefore the aim of the study was to analyse Latvian dairy herd colostrum quality. Colostrum was collected from Holstein Black cows within the first six hours after calving, lactation period of animals ranged from 1st to 4th lactation. Colostrum samples (n=51, 50 mL) were collected from December 2018 to February 2019. Immunoglobulin concentration (n=51) was defined by colostrometer (COLOSTROMETERtm Biogenics, USA), total solids content by optical refractometer (Model BX, UK). Staphylococcus spp. colony–forming unit (CFU) (LVS EN ISO 6888-1+A1:2007), the presence of Listeria spp. (LVS EN ISO 11290-1+A1:2007) and Salmonella spp. (LVS EN ISO 6579-1:2017) were examined in the colostrum samples (n=20). Despite the high immunoglobulin concentration in the analysed samples, our research findings demonstrate suboptimal colostrum quality received by calves. That indicates the necessity for regular colostrum quality control and better management practise providing on the farm.

Two recombinant influenza A virus vectors expressing the ESAT 6 and TB10.4 mycobacterial proteins from the non-structural (NS) gene were constructed via reverse genetics technique to develop a specific means of prophylaxis for bovine tuberculosis. We experimented to determine optimal conditions for growing recombinant vectors in Vero cell culture and chick embryos. This study established that the maximum amount of virus builds up in a Vero cell culture with the Dulbecco’s Modified Eagle’s Medium (DMEM) serum-free medium. However, using cell culture to produce vector vaccines is labour-intensive and inefficient. An alternative way, a traditional, time-tested technique, is provided by growing samples in chick embryos. One of the advantages of this technique is its affordability and availability, enabling easy scale-up of vaccine production. In the optimization experiments, the FLU-ΔNS_ESAT 6 and FLU-ΔNS_ТВ10.4 viruses constructed were inoculated into 10-day-old chick embryos. It was determined that the optimal incubation temperature that led to the highest virus build-up was 37 ± 0.5 °С. And the infectious activity level of the FLU-ΔNS_ESAT 6 recombinant vector was at 8.95 ± 0.07 log10EID50 0.2 cmE−3, while that of the FLU-ΔNS_ТВ10.4 was at 9.20 ± 0.07 log10EID50 0.2 cmE−3, what was provided by infectious doses of 1000–10000 EID50 , which makes it possible to create a virus-containing material with a hemagglutination activity level of 1:64. The size of recombinant vector amplicons expressing proteins ТВ10.4 and ESAT 6 was 1170 bp and 1175 bp, respectively. Electron microscopy images confirm that the developed virions are morphologically similar to the avian influenza virus.