In what situation should a veterinarian be contacted immediately?

A veterinarian should be contacted immediately in a situation involving severe trauma or inability to bear weight on a limb because these symptoms often indicate a critical condition that may require urgent medical intervention. Severe trauma can include broken bones, internal injuries, or significant soft tissue damage, which can lead to serious complications if not addressed quickly. The inability to bear weight can suggest pain or injury that might require diagnostic imaging or surgery.

In contrast, the other choices involve issues that can often be managed with less immediate attention. Minor cuts and scrapes typically do not pose a risk to the horse's overall health unless there are signs of infection or significant blood loss. Routine vaccinations are scheduled events that can be planned and do not require urgent care. Frequent sneezing may indicate allergies or other issues but is generally not an emergency unless accompanied by serious symptoms such as difficulty breathing or significant nasal discharge.