I have a 4 -coming 5 year old OTTB. A month ago he had severe diarrhea for a few days and the vet had him on biosponge for a week and it went away. Now a week and a half ago, it came back. He was put back on biosponge but it is not making a difference this time..The vet will be back out on Monday. Just wondering if anyone has any idea? He ran his last race in July of 2011 and retired healthy and sound. UTD on everything. He is a very laid back horse, but is in a smallish stable majority of the time-in which he paces all day and chews on wood often. Also, he is on grass hay only..