SummaryReasons for performing study: The intestinal bacterial community of the horse is a key determinant of intestinal and whole-body health. Understanding the bacterial community structure and function is an important foundation for studies of intestinal health and disease.Objectives: To describe the faecal bacterial community and the volatile organic compounds (VOCs) of the faecal metabolome of healthy Thoroughbred (Tb) racehorses, and to characterise responses to dietary supplementation with amylase-rich malt extract.Study Design: This was an intervention study performed with eight privately-owned Thoroughbred racehorses in active race training. Faecal samples were collected noninvasively before and six weeks after supplementation.Methods: Faecal metabolome was characterised using thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS), with spectral analysis performed using AMDIS and compared against the NIST database. Taxonomic description of the faecal microbiota was achieved using error-corrected 454 pyrosequencing data from 16S rRNA gene amplicons. Results:The faecal metabolome of our study population was dominated by organic acids, alcohols and ketones. We identified 81 different VOCs only 28 of which were present in >50% of samples indicating functional diversity. Faecal VOC profiles differed between first and second sampling point, some VOCs being significantly reduced post-supplementation, consistent with a marked response to dietary amylase-rich malt extract. Faecal microbiota was characterised as highly diverse; samples demonstrated verifiable diversity in the range 1200-3000 operational taxonomic units (OTUs) per individual. The methods used also 3 describe high levels of infrequent, low abundance OTUs. Faecal microbial community structure was found to be different following dietary supplementation. Differences in several low-abundance bacterial taxa were detected and also some evidence of inter-horse variation in response. Conclusions:The volatile faecal metabolome of Tb racehorses is dominated by organic acids, alcohols and ketones; this study demonstrates that dietary supplementation with amylase-rich malt extract may significantly alter the profile of VOCs. The faecal microbiome is highly diverse, dominated by Firmicutes and Bacteroidetes. Small but significant changes in microbial community structure were detected following dietary supplementation.Potential relevance: This study describes the faecal metabolome and microbiome of healthy Tb racehorses against which future studies of disease and dietary intervention can be benchmarked.4

Diagnosis of colorectal cancer is an invasive and expensive colonoscopy, which is usually carried out after a positive screening test. Unfortunately, existing screening tests lack specificity and sensitivity, hence many unnecessary colonoscopies are performed. Here we report on a potential new screening test for colorectal cancer based on the analysis of volatile organic compounds (VOCs) in the headspace of faecal samples. Faecal samples were obtained from subjects who had a positive faecal occult blood sample (FOBT). Subjects subsequently had colonoscopies performed to classify them into low risk (non-cancer) and high risk (colorectal cancer) groups. Volatile organic compounds were analysed by selected ion flow tube mass spectrometry (SIFT-MS) and then data were analysed using both univariate and multivariate statistical methods. Ions most likely from hydrogen sulphide, dimethyl sulphide and dimethyl disulphide are statistically significantly higher in samples from high risk rather than low risk subjects. Results using multivariate methods show that the test gives a correct classification of 75% with 78% specificity and 72% sensitivity on FOBT positive samples, offering a potentially effective alternative to FOBT.

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SIFT-MS is used for the first time in profiling the volatile organic profile in faecal headspace in two groups of horses admitted to an equine hospital, one group with acute intestinal disease (colic) affecting the large colon, plus a control group of similarly managed horses admitted for non-gastrointestinal/metabolic reasons (e.g. acute orthopaedic injury). Compounds in faecal headspace which show statistically significant concentration differences between the groups are acetone and methanol. In addition, some ions at various m/z values show significantly different ion counts between the groups. Further information may be gleaned by using multivariate statistics in evaluating the differences between the two horse groups. Principal components analysis (PCA) and orthogonal partial least squares discriminant analysis (OPLS-DA)were evaluated for reducing the dimensionality of the SIFT-MS data, and OPLS-DA was found to be best at discriminating between the groups, particularly with SIFT-MS data acquired using the H 3 O + precursor ion.Analysis of these data also show the significance of ammonia as a discriminating ion. These results show that SIFT-MS may potentially be used on the headspace of horse faecal samples for detecting altered microbial fermentation associated with acute intestinal disease of the colon.