Application of the lactose ¹³C-ureide breath test for measurement of equine orocaecal transit time

<b>Reasons for performing study:</b> Application of the lactose <sup>13</sup>C-ureide breath test (LUBT) for measurement of equine orocaecal transit time (OCTT) has not been reported previously. The ability to assess OCTT noninvasively, and to investigate its relationship to gastric emptying rate and small intestinal transit, would be of both clinical and research value.<p></p> <b>Objectives:</b> 1) Assessment of the LUBT in healthy horses, with comparison of induced versus noninduced test protocols. 2) Application of a new dual stable isotope breath test (lactose <sup>13</sup>C-ureide and <sup>13</sup>C-octanoic acid) for gastrointestinal transit measurement.<p></p> <b>Hypothesis:</b> The LUBT will allow quantification of equine OCTT, and test efficacy will be enhanced by prior administration of lactose <sup>12</sup>C-ureide as shown in vitro. The dual tracer breath test will permit simultaneous measurement of gastric emptying, OCTT and small bowel transit times.<p></p> <b>Methods:</b> Induced and noninduced LUBTs were performed in 3 healthy mature horses in randomised order using a standard test meal and protocol. Combined LUBT and <sup>13</sup>C-octanoic acid breath tests (<sup>13</sup>C-OABT) were performed in 4 individuals on 4 occasions at weekly intervals. Expiratory isotopic recovery was modelled to allow generation of gastric emptying data, small bowel transit times and caecal transit parameters.<p></p> <b>Results:</b> The induction protocol for the LUBT increased the rate and magnitude of expiratory <sup>13</sup>CO<sub>2</sub> significantly. Mean ± s.d. values for OCTT, caecal lag phase (t<sub>lag</sub>) and caecal t<sub>1/2</sub> using the induced LUBT were 3.24 ± 0.65 h, 5.62 ± 1.22 h and 6.31 ± 1.21 h, respectively. Dual stable isotope tests resulted in the production of 2 discrete peaks in expiratory <sup>13</sup>CO<sub>2</sub> in 15/16 tests from which gastric t<sub>1/2</sub>, OCTT and small bowel transit (SBT) parameters could be calculated.<p></p> <b>Conclusions:</b> The induced LUBT provides a reliable noninvasive measure of equine OCTT and can be paired with the <sup>13</sup>C-OABT to provide further information about small intestinal motility.<p></p&gt