There are many signs your horse will show you that he is sick. Here are some: holding its head low, not responsive to sounds, discharge from nose, eyes or mouth, abnormal breathing, fever, dull coat, excessive sweating, not eating or drinking, dehydrated (lift the skin, if it doesn't go back immediately , it could be a sign), not eating or drinking, diarrhea or constipation, pacing, kicking, pawing, unpleasant or unusual odor, bleeding, limping, pale, white, yellow, blue or black mucous membranes and more. If you suspect your horse is ill, call the vet immediately and give as much information as you can.