Abstract / Summary
Abstract Bovine tuberculosis (bTB) is a chronic disease primarily caused by Mycobacterium bovis , a zoonotic pathogen with worldwide distribution that causes economic losses in milk and meat production systems. In dairy cattle from central Chile, disease prevalence remains high, and the national control and eradication program has faced the reluctance of producers to implement the test-and-slaughter strategy due to the lack of compensation. Within this epidemiological context, vaccination with the M. bovis Bacillus Calmette-Guerin (BCG) strain has proven to be a useful tool for disease prevention and control and has shown non-specific effects in humans and animals. The objective of this study was to assess non-specific immunological responses of peripheral blood monocytes and the impact on dairy production traits following vaccination with the BCG Russia strain administered in a two-dose scheme, in a commercial dairy farm with a free bTB status. A total of 198 12-month-old heifers were vaccinated via the subcutaneous route with the equivalent of 1 human dose of BCG. Ninety-six of them were revaccinated with a similar dose during first 30 d of their lactation period. In addition, 39 control animals were not vaccinated and received saline. Pro-inflammatory cytokine responses to ex-vivo homologous (PPD-B) and heterologous (LPS) stimulation was evaluated in peripheral CD14 + monocytes in a subgroup of animals to evaluate innate immunity response. Milk parameters at the first and second lactation periods were also compared among groups. Vaccinated and revaccinated animals exhibited increased expression of IL-6 and TNF-α in CD14 + monocytes in response to ex vivo homologous and heterologous stimulation, suggesting the induction of non-specific innate immune activation in these cells. Moreover, higher milk yields, changes in milk fat and protein levels and lower subclinical mastitis cases were observed during the second lactation period, in those vaccinated and revaccinated animals compared to unvaccinated cows (p < 0.05). These results indicate that BCG vaccination confers sustained non-specific effects in animals under commercial management conditions, providing potential benefits to support its implementation as a bTB control tool in dairy cattle.