## 2 Results  
### Assessment of Volatile Organic Compound Collection  
Breath and fecal VOC samples were collected and analyzed using various flow rates and times on three different days in order to assess collection methods that were most effective in capturing VOC from swine (summarized in Table 1 and Supplementary Figures S1 and S2).  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & & & **Day** & \\ \cline{3-5}
**Sample Source** & **Flow Rate** & **1** & **2** & **3** \\ \hline \multirow{6}{*}{Breath} & 100 mL/min for 1 min & & & \\  & 100 mL/min for 2 min & & & \\  & 200 mL/min for 1 min & & & \\  & 200 mL/min for 2 min & & & \\  & 1L/min for 1 min & & & \\  & 1L/min for 2 min & & & \\ \hline \multirow{6}{*}{Feces} & 200 mL/min for 2 min & & & \\  & 200 mL/min for 5 min & & & \\ \cline{1-1}  & 200 mL/min for 10 min & & & \\ \cline{1-1} \cline{2-5}  & 200 mL/min for 2 min & & & \\ \cline{1-1} \cline{2-5}  & 200 mL/min for 5 min & & & \\ \cline{1-1} \cline{2-5}  & 200 mL/min for 10 min & & & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Breath and fecal volatile organic compound (VOC) samples that produced good chromatographic signals on each collection day. Breath VOC samples were collected from one animal over three days at a rate of 100 mL/min for 1 min, 100 mL/min for 2 min, 200 mL/min for 1 min, 200 mL/min for 2 min, 1 L/min for 1 min, and 1 L/min for 2 min. Fecal headspace air was collected from one animal over three days at a rate of 200 mL/min for 2 min, 200 mL/min for 5 min, and 200 mL/min for 10 min. Three samples were obtained under each condition.  
For the samples collected on the first day (Figure S1a), good chromatographic signals were obtained for those collected at 1 L/min for 1 min and 1L/min for 2 min, with better shape and slightly better intensity in the case of the 1 L/min for 1 min samples. Practically no chromatographic signals were obtained in the other cases. For the samples collected on the second day (Figure S1b), good chromatographic signals were obtained for all samples collected at 1 L/min and 200 mL/min, with better shape and slightly better intensity in the case of the 200 L/min for 1 min samples. For the samples collected on the third day (Figure S1c), no chromatographic peaks could be detected. The air samples collected both before and after the breath sample collection did not produce any noticeable signals.  
Next, quality control analysis was performed by measuring the second portion of Tenax material of the samples that produced better chromatographic signals on the first two days of collection (i.e., samples acquired at 1 L/min for 1 min on the first collection day and at 200 mL/min for 1 min on the second collection day). These analyses (shown in Figure S1d) revealed that in the case of the sample acquired at 1 L/min for 1 min, no compound was identified in the second portion of the Tenax material; therefore, VOC pre-concentration was adequate in this case. This was in contrast with the sample acquired at 200 mL/min for 1 min, where various compounds were not retained by the first portion of Tenax and passed to the second one. Therefore, these analyses suggested that the best flow rate for the transfer of the breath volatiles to the storage cartridge was 1 L/min for 1 min.  
For the fecal samples, the best flow rate for VOC transfer to Tenax was found to be 200 mL/min for 10 min, as evident in Figure S2. The areas of the most abundant chromatographic peaks were notably (visibly or apparently) higher in this case than in the other two cases on the two first collection days and quite similar on the third collection day.