Strengthening Tuberculosis Control Through Biosecurity in Vaccinated Herds

BCG vaccination can help reduce the impact of bovine tuberculosis (bTB), but vaccination alone is unlikely to eliminate disease from an infected herd. Like most infectious disease control programs, vaccination delivers better outcomes when combined with effective biosecurity measures. Reducing opportunities for pathogen transmission within and between animal groups strengthens the overall impact of vaccination and supports long-term herd health^1,2. 

Why Biosecurity Still Matters 

Even in vaccinated herds, infected animals can continue to serve as sources of infection. Biosecurity minimizes exposure of susceptible cattle, reduces environmental contamination, and complements the protective effect of vaccination. Practical management changes can therefore play a significant role in limiting disease spread throughout the herd¹. 

Protect Young Stock from Early Exposure 

Young calves should be managed to minimize contact with potential sources of Mycobacterium bovis. 

Key recommendations include^1,2: 

• Feed calves only colostrum from healthy cows or heat-treated colostrum to reduce the risk of infection while maintaining good passive immunity. 

• Use milk from healthy cows or milk replacer rather than milk from infected animals, as the digestive tract can serve as a route of infection, particularly in cases of tuberculous mastitis. 

• Maintain effective physical separation between calf pens and adult infected cattle to prevent transmission through close contact, contaminated feed, water, or fomites. 

Protecting calves during this early stage helps reduce infection pressure before animals enter the adult herd. 

Improve Herd Management Practices 

Routine management practices can influence disease transmission within vaccinated herds. 

Veterinarians should encourage producers to^1,2: 

• Avoid feeding waste feed from infected adult pens to calves, heifers, or dry cows, as contaminated feed may contribute to disease spread. 

• Organize water flow so that water moves from TB-free groups toward infected groups rather than in the opposite direction. 

• Milk healthy cows before infected or suspect animals to reduce opportunities for contamination. 

Although these measures may appear simple, together they reduce opportunities for indirect transmission within the farm. 

Control Animal Movement 

Introducing infected animals remains one of the most important routes by which tuberculosis enters a herd¹. 

Whenever possible: 

• Use replacement animals from the same herd or from herds confirmed to be TB-free. 

• Carefully evaluate the disease status of purchased cattle before introduction. 

• Manage tuberculin-reacting animals separately from the remainder of the herd. 

Limiting unnecessary animal movement and maintaining separation between infected and non-infected groups supports both vaccination and disease-control efforts. 

Strengthen Farm Biosecurity Beyond the Herd 

Biosecurity extends beyond cattle management. 

Additional measures include: 

• Prevent outside vehicles from entering animal housing areas. 

• Take appropriate precautions when cattle attend fairs, exhibitions, or other events where exposure to infected animals may occur. 

• Organize housing to maintain separation between infected and disease-free groups whenever possible. 

These practices help reduce the introduction and spread of infection both within the farm and from external sources. 

Practical Clinical Insights 

Biosecurity should be discussed alongside vaccination during every herd health consultation. Reviewing calf-rearing practices, replacement policies, water and feed management, and animal movement can identify weaknesses that may reduce the overall success of a vaccination program. 

Small improvements implemented consistently across the farm often have a greater long-term impact than relying on vaccination alone. 

Take-Home Message 

BCG vaccination is most effective when supported by practical biosecurity measures. Protecting calves, maintaining separation between animal groups, managing feed and water carefully, controlling animal introductions, and reducing opportunities for disease transmission all contribute to stronger tuberculosis control. For practicing veterinarians, combining vaccination with sound biosecurity provides a more comprehensive and sustainable approach to managing bovine tuberculosis in infected herds. 

Reference 

1. Milián-Suazo F, González-Ruiz S, Contreras-Magallanes YG, Sosa-Gallegos SL, Bárcenas-Reyes I, Cantó-Alarcón GJ, Rodríguez-Hernández E. Vaccination strategies in a potential use of the vaccine against bovine tuberculosis in infected herds. Animals. 2022 Dec 1;12(23):3377. https://www.mdpi.com/2076-2615/12/23/3377 
2. Xu F, Tian L, Li Y, Zhang X, Qi Y, Jing Z, Pan Y, Zhang L, Fan X, Wang M, Zeng Q. High prevalence of extrapulmonary tuberculosis in dairy farms: Evidence for possible gastrointestinal transmission. PLoS One. 2021 Mar 30;16(3):e0249341. https://journals.plos.org/plosone/article/file?id=10.1371/journal.pone.0249341&type=printable