I am by no means one of the experts, but I think i can answer this for you. Cleaning up after your horse is always important, but out on a trial ride in the wilderness it might not be necessary. It would be important to follow the rules of where you are riding and if it is a public area or state park there are probably guidelines in place. In areas where you park your trailer is would be important to keep it clean for the next people who come along. Cleaning up after your horse will definitely help to keep the flies down.
.