Oral malodour in dogs is not only unpleasant for owners but is also frequently an indicator of underlying disease. Volatile sulphur compounds (VSCs), such as methyl mercaptan (CH3SH), hydrogen sulphide (H2S) and dimethyl sulphide ((CH3)2S), are produced by specific bacteria residing in the oral cavity. It is these compounds that are perceived as unpleasant by humans. Even low concentrations of VSCs can be toxic to tissues, increasing mucosal membrane permeability and initiating an inflammatory response that serves as a trigger for periodontal disease. In humans, VSC-producing bacteria such as Fusobacterium, Treponema, Porphyromonas and Peptostreptococcus tend to accumulate in the posterior dorsal tongue, gingival crevices, periodontal pockets and saliva.

Many studies of canine oral malodour have relied upon gas sensor instruments such as the Halimeter®, typically collecting breath samples whilst dogs are under general anaesthesia, to provide quantitative measurement of halitosis. This study evaluated canine breath using an OralChroma™ portable gas chromatograph, considered a highly sensitive alternative to the Halimeter® that can measure additional compounds. VSCs were assessed in breath from 14 dogs trained to enable conscious breath sample collection, housed at the Waltham Petcare Science Institute (Ethics approval 54961). This approach, coupled with an induced malodour model where an amino acid solution is used create malodour, enabled real-time analysis of VSC levels following single instance oral interventions e.g. two minutes brushing or provision of a dental chew.

Previous insights had highlighted that the variety of hard and soft surfaces in the canine oral cavity create multiple different ecological niches for microbial growth. By combining malodour measurement with plaque and tongue scrapings it was possible to correlate bacterial loads with VSC detection in breath. Malodour-causing bacteria were found to be highly abundant on the tongue. Initial characterisation by 16S sequencing revealed 19 operational taxonomic units from 50 samples with genera dominated by Actinomyces (27.5%), Fusobacteria (17.5%) and Porphyromonas (12.5%). The main species identified as black pigmenting, VSC-producing bacteria were from the genera Fusobacterium and Porphyromonas, a finding comparable to human studies.

Applying one-time interventions in the induced malodour model reduced key VSCs compared to no intervention. Interventions (dental chews) which targeted multiple areas of the canine oral cavity had the greatest impact, significantly reducing levels of H2S (p<0.001), CH3SH (p<0.05), total bacterial load and VSC-producing bacterial load (p<0.001) compared to no intervention. This research highlights the value of more sensitive measurement techniques for oral malodour detection in conscious dogs and indicates that targeting areas of the mouth beyond the buccal tooth surface is a helpful tactic to disrupt oral niches harbouring VSC-producing bacteria.