A: The most important thing in assessing a horse for pain is knowing what normal looks like. That is, what is normal for any horse, and what is normal for each individual horse. You will never know what abnormal is if you don’t know what normal is.
For example: When and how often does your horse lie down? How does your horse normally interact with other horses in his turnout group? Does your horse come to the front of the stall to greet you? Does he always clean up his feed right away? What is his normal posture at rest? What are his usual facial expressions?
I have a herd of eleven Shetland ponies, and I regularly spend time watching them. I know their resting patterns, so I could see that one pony was lying down just a little more than normal and detected early laminitis before she was actually walking abnormally.
I know which ponies are submissive and hang back a bit at feeding time, so I can distinguish who doesn’t have a good appetite and who is just assessing the herd dynamics before she chooses which pile of hay to go eat at. One mare was just holding her head at a little different angle, which triggered closer inspection, and I found she had painful, enlarged lymph nodes. My skills are far from extraordinary. They are just borne from an effort to observe with a critical eye, which is something anyone can learn to do.
Pain associated with lameness can be very tricky. “Head-nodding” during movement is probably the most reliable and consistent sign that a horse is lame. However, more subtle signs might be associated with just a change in the vigor in which the horse moves out, or with how quickly the horse fatigues in a training session. It’s always helpful to have someone jog your horse in hand for you on a regular basis. This way you can learn what kind of mover your horse is normally. For example, is he somewhat choppy in front, does he wing in front, or cross-over behind?
One of the most important things you can do to assess pain is to learn to take your horse’s heart rate, either by using a stethoscope or feeling pulses. I have learned in practice that heart rates rarely lie. A high heart rate, though it can mean many things medically, is often associated with pain. It can help distinguish between a milder colic in a horse showing dramatic behaviors from a more severe colic in a stoic horse.
It is always, always time well spent closely watching your horse’s behavior. Nothing can replace an owner or caretaker’s good observational skills to make an early assessment of sometimes very subtle changes in a horse’s behavior. Create a mental, and if it helps, even a physical, catalog or image of your horse’s normal set of behaviors inside, outside, and at work.