Here's why:
* Trush is a condition that affects the frog of a horse's hoof. It's caused by a buildup of bacteria and debris in the moist, dark environment of the frog. This leads to inflammation, a foul odor, and can even progress to abscesses.
Let's break down the other options:
* Patchy raw areas of skin on the back could be caused by various issues like allergies, insect bites, or fungal infections. It's not directly related to trush.
* Excessive rolling done by horse could indicate pain or discomfort but isn't specifically related to trush.
* Deep bruising can happen in various areas of the horse's body, not just the hoof. While bruising can be a symptom of trush, it's not the defining characteristic.
Important Note: If you suspect your horse has trush, it's essential to consult a veterinarian for proper diagnosis and treatment.