Which of the following is a sign of conjunctivitis in cavies?

The pink appearance of the eye's white part is a clear indicator of conjunctivitis in cavies. This condition, also known as inflammation of the conjunctiva, often manifests with redness and swelling, making the typically white part of the eye appear pink or red. This change is an important sign that the tissue is irritated or inflamed, which can be due to various factors such as infection, allergies, or foreign bodies.

In contrast, while weight loss, excessive grooming, and loss of appetite can indicate health issues in cavies, they are not specific signs of conjunctivitis. Weight loss and loss of appetite could be associated with a variety of illnesses, and excessive grooming might suggest discomfort or stress but does not directly correlate with eye health. Therefore, the pink appearance of the eye's white part is the most relevant sign indicating conjunctivitis in cavies.