Which of the following is NOT part of the core vaccines recommended for horses?

The choice of Brucellosis as the option that is not part of the core vaccines recommended for horses is appropriate because Brucellosis primarily affects cattle and does not pose a significant risk to equine populations. Core vaccines for horses are vaccines that are recommended for all horses because they protect against diseases that pose a high risk and can have serious consequences. These core vaccines typically include those that protect against Tetanus, Equine Influenza, and Rabies, all of which are significant health concerns for horses.

In particular, Tetanus is caused by bacteria that can enter the body through wounds, Equine Influenza is a highly contagious respiratory disease, and Rabies is a fatal viral illness that can affect both animals and humans. Since Brucellosis does not represent a direct threat to horses and is not a common practice to vaccinate horses for this disease, it is correctly identified as the option that does not belong in the group of core vaccines.