Abstract

Bovine tuberculosis (bTB) is mainly caused by Mycobacterium bovis, which affects cattle, leading to significant economic losses. In Chile, the vaccination with the M. bovis Bacillus Calmette-Guérin (BCG) strain has been implemented in dairy herds with high prevalence of bTB. This study evaluated non-specific protection associated with BCG on the detection of pathogen-associated genes (nsp5, stx1, stx2, invA, IS1081) and mortality related to diarrhea and pneumonia in calves. A total of 186 calves from a commercial dairy farm were enrolled and grouped as vaccinated (n = 96) and non-vaccinated (n = 90). The BCG Russia strain (2–5 × 105 UFC) was inoculated subcutaneously within the first 30 days after birth. Animals were monitored through fecal sampling at 3 and 6 months of age for molecular detection of gene sequences. A logistic regression analysis showed differences in detection rates of the stx1 sequence at 3 months, with a higher risk for the non-vaccinated individuals (OR 2.91, CI 1.42–5.94, p = 0.03) and for those born in the cold season (OR 9.55, CI 2.02–45.11, p = 0.004). A Kaplan–Meier survival analysis showed a significant difference in deaths in vaccinated calves compared with non-vaccinated animals (p = 0.018), suggesting that BCG confers non-specific protection during the first 3 months after birth, in field conditions. © 2025 by the authors.