Over the last 39+ years, I have dealt with horse distemper, colic, and barbed-wire caused injuries. This last week I had an experience with a horse with colic.
http://en.wikipedia.org/wiki/Horse_colic. The owners thought that perhaps the partner horse "worried" the other horse by constantly moving him around. In the past, I have had horses colic and not be on pasture. This horse had symptoms which were unlike others that I have dealt with. There was no rolling, only lying down. Actually, the horse was eating while he was lying down!
I put a halter on him, and pulled him up to a standing position. I walked him around for a few minutes and he appeared fine. I left him in the pasture and called the owners. They asked me to remove both of their horses to a non-pasture holding pen and not give the ailing horse any feed. I know that walking a horse is the standard prescription for a horse with a tummy ache. I began walking him, but he continued to try to eat any grass that was available to him. He did not need to be pulled along--he was very willing to walk - again, unlike "colicy" horses that I have worked with in the past. I put him in the round pen and he immediately began to drink water. Generally a horse with colic is unwilling to drink. We hauled him to the vet, he stayed overnight there, and then returned to the pasture a few days later. He had collicked, but we caught it early.
About a week later after this incident, I noticed one of my own horses with his eye half-swollen shut. I could not figure out what was wrong. I called the vet and he sent some medicine home with my daughter. All of a sudden, the area under his mouth was swollen, which could indicate "strangles". http://www.omafra.gov.on.ca/english/livestock/horses/facts/03-037.htm
I found a YouTube video which I have embedded on "strangles" (see top of page). I recently was told that strangles and distemper in horses are the same name for the same disease.
Another condition which I have encountered in the last two years is laminitis, or founder, as it is also called. http://www.recoveryeq.com/laminitis_founder_pro.htm. In my Jing recording above, you can view another condition I encountered one summer--a horse who came to camp with an injury that led to an atrophied leg muscle.