Symptom
It is the manifestation of a disorder in the animal. The difference between symptom and sign is that the symptom is a subjective reference which the patient gives as a result of a change recognized as abnormal (e.g. pain), while a sign is an objective fact (e.g. fever, which can be measured with a thermometer). However, in practice, they are often used as synonymous.
Some of the symptoms that can be seen on a farm are diarrhoea, cough, fever, reduced water and feed intake, reduced activity...