Which of the following horses exhibits the most signs of internal parasite infestation?

The selection of the option that describes a horse with a pot-bellied appearance, rough coat, and coughing as exhibiting the most signs of internal parasite infestation is accurate. Internal parasites can significantly impact a horse's overall health and well-being. A pot-bellied appearance is a classic sign of parasitic infection, as it suggests that the horse may be experiencing gastrointestinal issues caused by worms or other parasites that can structure feeding and nutrient absorption.

A rough coat often indicates poor nutrition or underlying health problems, which can be exacerbated by the presence of parasites that compromise the horse’s ability to utilize feed effectively. Coughing can be associated with various health issues, including respiratory problems that may arise indirectly due to the systemic effects of parasites or through secondary infections that can occur in an immunocompromised state.

In contrast, the other options describe horses that display signs of good health, such as having a healthy coat, being energetic, well-muscled, shiny coats, or having an active and normal appetite. These characteristics generally indicate that the horses are free from significant internal parasite burdens and are likely receiving adequate nutrition and care. Therefore, the signs exhibited in this choice distinctly align with common symptoms of internal parasite infestation.