The mucus may be sluffed intestional wall tissue. In most cases it is
not a problem althought it should always get your mental wheels
spinning. Why did it sluff-off now? Often it's stress related but an
increase in core temperature seems to also promote the discharge.
As for a response, we look for ways to reduce the temperature of the
horse during rides and increase probiotic administration. We also look
for ways to reduce the horses emotional stress (i.e. pacing, TTeam-work,
finding a trail buddy, etc.).
Hope this answers your question.
Ramey and Cynthia Peticolas-Stroud