Continuous real-time breath analysis in ruminants: Effect of eructation on exhaled VOC profiles

The analysis of volatile organic compounds (VOCs) allows non-invasive investigations of diseases. Animal studies are conducted as a model to perform research of VOCs and their relation to diseases. In large animal models ruminants were often used as experimental animal. The effect of their physiological eructation on VOC exhalation has not been examined yet and is the objective of this study.
 Methods: Continuous breath profiles of 2 young cattle, 4 adult goats and 4 adult sheep were measured through a mask, covering mouth and nose, in real-time (200 ms) by means of PTR-TOF-MS. Each animal was analysed twelve times for 3 consecutive minutes. 
 Results: Real-time monitoring yielded in a distinction of different phases in the breath profiles of ruminants. An algorithm to separate eructation- and breath phases was established. In the first exhalation after eructation at least 19 VOC concentrations increased (up to 36 -fold) and went back to initial levels in subsequent exhalations in all investigated ruminants. Decay of concentrations was substance specific. In goats, less VOCs were affected by the eructation compared to cattle and sheep. Breath profiles without exclusion of ructus phases showed higher variations and median values than profiles where eructation phases were excluded. 
 Conclusion: Real-time breath analysis of ruminants enables the discrimination and characterisation of breath and eructation phases. This leads to a better understanding of variation in breath data and possible origins of VOCs: breath or digestion related. To avoid impairment of breath gas results and to gain further information on bacterial products from the rumen, eructation and pure breath data should be analysed separately. &#13.