• horse;
  • lactose 13C-ureide breath test;
  • orocaecal transit time;
  • hydrogen breath test


Reasons for performing study: Validation of a reliable, noninvasive clinical test for quantification of equine orocaecal transit time (OCTT) is required. This would facilitate an evidence-based approach to investigation and treatment of equine small intestinal disorders.

Objectives: 1) Comparison of the lactose 13C-ureide breath test (LUBT) with the hydrogen breath test (H2BT) for OCTT measurement. 2) Identification of the characteristics of gastrointestinal microbial glycosylureide hydrolase activity in vitro. 3) Production of an optimised protocol for the LUBT for in vivo measurement of equine OCTT.

Hypothesis: Significant lactose 13C-ureide (13C-LU) hydrolase activity is restricted to the large bowel. The rate of expiratory 13CO2 production after ingestion of the isotope will provide an indirect quantifiable measure of orocaecal transit rate. Requisite bacterial activity may be enhanced by a primer dose of unlabelled substrate as shown in Man.

Methods: Combined LUBT and H2BT were performed in 8 healthy individuals. Analysis of sequential end expiratory breath samples was used to calculate OCTT and results compared. Digestion of 13C-LU was investigated in vitro using fresh faecal material or intestinal aliquots collected post mortem. Isotopic fermentation rate was measured by rate of appearance of 13CO2.

Results: Peaks in expiratory 13CO2 occurred in all individuals after ingestion of the labelled test meal, whereas H2 expiration was variable. Both faecal and intestinal microbial digestion of 13C-LU were maximised by prior exposure to 12C-LU. Induced bacterial glucoseureide hydrolase activity was significantly greater in the caecum than in the small intestine (n = 10, P<0.05).

Conclusions: Significant 13C-LU digestion is restricted to the equine large intestine under normal conditions, and is enhanced by prior exposure to 12C-LU, making 13C-LU a suitable noninvasive marker of equine OCTT. The LUBT is more reliable than the H2BT for measurement of equine OCTT.