Herding is done predominantly by breeds developed over centuries to millennia specifically for that purpose. Working-level herding breed dogs are intense, high-drive dogs that will work despite severe illness or pain, thereby masking clues that they are ailing or the nature of their problem. The handler should recognize subtle changes that might signal ill health, and veterinarians should take an active role in training handlers on essential skills. Herding dogs typically work entirely outdoors in rural to wilderness environments with continuous exposure to other domestic animals and wildlife and may be affected by trauma, toxin exposure, infectious diseases, and parasitic infections.