What is used to vaccinate heifers for Brucellosis and can rarely be shed in milk?

• A. Strain RB51
• B. Strain RB58
• C. Strain S19
• D. Strain RB50

Answer: (A)

Vaccination of heifers against brucellosis uses a live attenuated Brucella abortus strain that can still appear in milk on rare occasions. The RB51 vaccine is the one specifically used for this purpose. It’s a rough mutant chosen because it minimizes interference with standard brucellosis tests and is safer for use in younger animals, including heifers. However, it can be shed in milk occasionally, so milk from recently vaccinated cows should be handled according to biosafety guidelines and typically pasteurized before consumption. Other strains, like S19, are older and can cause abortions in pregnant cows and interfere with serological testing, while RB50 and RB58 are not the standard vaccines used for this purpose.