A rider might think that when his or her horse chews the bit and salivates that it provides a calming effect. Yet, there might be other gastrointestinal benefits to bit chewing that could help improve progressive gastrointestinal motility for horses with ileus.
A recent study by researchers at the veterinary schools in Louisiana and Virginia looked at the effects of bit chewing on the GI tract during post-operative ileus, which, without resolution, is associated with 86% mortality [Patton, M.; Leise, B.; Baker, R.; Andrews, F. The effects of bit chewing on borborygmi, duodenal motility and gastrointestinal transit time in clinically normal horses. Veterinary Surgery 2021; DOI: 10.1111/vsu.13745].
While feeding is a known stimulator of intestinal motility, this is not a practical option for post-operative horses, particularly those with compromised motility. The authors noted, “The idea of bit chewing in the horse was inspired from reports of using gum chewing postoperatively in people as a common means to stimulate the cephalic-vagal response in attempts to stimulate the GIT without overwhelming the intestine with feed.”
The study assigned six healthy horses to one of two groups for a week—three fitted with an apple-flavored snaffle bit or three in a control group with no bit. Each horse experienced both bit possibilities—apple-flavored or no bit—with a 2-week washout between trials. Every six hours, the bit was placed in the horses’ interdental space for 20 minutes with a snug enough fit to encourage continual chewing. Five minutes following bit placement, duodenal contractions were evaluated with ultrasound and borborygmi were evaluated by auscultation—these parameters were assessed every 12 hours. Additionally, the gastrointestinal transit time (GTT) was measured by nasogastric administration of 200 colored beads with manure collection every three hours until 80% of the beads were recovered or until the elapse of seven days. The horses were fasted for 12 hours prior to and again after bead administration, then pelleted feed and hay gradually increased to reach full rations by 54 hours.
The horses with the bit had a shortened GI transit time than the horses without a bit. Four of the six horses passed 80% of the beads and all passed at least 50%. Bead recovery was not statistically different between controls and bitted individuals for passage of 50%; however, horses that passed 80% of the beads demonstrated improved GI transit time with bit chewing compared to the controls. Duodenal contractions and borborygmi were no different between bitted or control groups.
While the results are not overwhelming, it is possible to use bit chewing as an adjunctive treatment for ileus in order to help speed up gastrointestinal transit time for cases with post-operative ileus. Future studies might shed more light on possibilities to resolve ileus.