If you are looking for authoritative references, several books provide a comprehensive bridge between ethology (the study of natural behavior) and clinical veterinary practice:
Subtle behavioral changes are often the first "red flags" for underlying medical issues, such as pain or metabolic disease. free zoophilia forum 2021
: A globally recognized standard for animal welfare that includes freedom from hunger/thirst, discomfort, and pain/injury/disease. If you are looking for authoritative references, several