Which of the following is a common sign of severe periodontal disease?

Halitosis, commonly known as bad breath, is a prevalent sign of severe periodontal disease in small animals. This condition arises from the buildup of plaque and bacteria on the teeth and gums, leading to inflammation, infection, and ultimately the release of volatile sulfur compounds that cause foul odor. The severity of periodontal disease often correlates with the degree of halitosis present, making it a significant indicator of dental health issues in pets.

While other signs like fever and excessive salivation can occur in various medical conditions, they are not specific indicators of severe periodontal disease. Fever may suggest systemic illness or infection but is not directly linked to periodontal issues. Excessive salivation can be associated with dental pain or other oral conditions but is not exclusively indicative of periodontal disease. Thus, halitosis stands out as the primary and most common sign directly related to severe periodontal problems in small animals.