Effect of a low dose of BCG-Phipps vaccine on the development of reactivity to tuberculin skin test in neonatal calves and adult cows

Bovine tuberculosis (bTB) has a direct impact in the productive and reproductive efficiency of dairy cattle. Nowadays, disease control programs based on tuberculin testing and removal of infected cattle are unaffordable for the developing countries, since there is no program of financial compensation, especially in high bTB-prevalence herds. Thus, control strategies based on vaccination are considered the best alternative. The aim of this study was to evaluate whether a low dose of BCG-Phipps vaccine induces reactivity to tuberculin skin test and its duration in neonatal calves and adult cows. For the analysis of the former, 69 TB-free Holstein-Friesian calves less than one-month old were used; of which, 54 calves were subcutaneously inoculated with 104 CFU of the BCG-Phipps vaccine, while the rest remained without vaccination. Under similar conditions of immunization, 133 single intradermal comparative cervical (SICCT) reactors and 133 non-reactors Holstein-Friesian cows of different age were also analyzed. In calves, the SICCT-reactivity was evaluated periodically in the first 14 months post-vaccination (mpv) while, in adult cows, the effect of vaccination on the test was evaluated at six months post-vaccination. A comparative ELISA was used by measuring the antibody levels in the groups. In calves, reactivity frequencies of 7.4 and 3.7% at 3 and 5 mpv, respectively were recorded. This reactivity disappeared at six months. None calves in the control group were reactor during the study. There were no variations in the degree of reactivity in the group adult reactor cows. However, in the non-reactor group, a conversion of 12.8% at six mpv was recorded. In addition, the conversion percentage was higher in older cows than in younger cows (p<0.05). The specific antibody levels did not increase in the vaccinated groups. Data indicate that the low dose of BCG-Phipps vaccine used had a reduced effect on the development of a delayed type hypersensitivity to tuberculin in neonatal calves, and heifers lesser than one-year-old. Key words: Bacillus Calmette-Guérin, bovine tuberculosis, M. bovis, single intradermal comparative tuberculin test.