The objective of this pilot study was to identify the odor-active compounds responsible for dog hair coat odor and to compare their levels in dry and wet dog hair.
A gas chromatography olfactometry (GCO) method was used to identify the important odor-active compounds from dog hair coat. One g of brushed hair from a healthy adult dog was placed in a 312 ml volume headspace cell. In the case of wetted hair, 1 g of water was sprayed on the hair. The cell was closed and allowed to equilibrate. At this point, the headspace air was pushed onto a Tenax trap and compounds were desorbed thermally followed by cryofocusing on a cold trap. The cold trap was then rapidly heated to 260° C during which time the volatile compounds entered the GC. The GC outlet was split 1:1 to FID and the olfactometry port. Six panelists trained in odor detection smelled the olfactometry port during the GC run. They noted the timing for the beginning and end of each odorant as well as the odor quality.
In the second phase of the study, relative amounts of the compounds identified by GCO were determined using the hair of six healthy dogs. Hair was collected and a 0.30 g aliquot of dog hair (dry or sprayed with 1 ml of water) was weighed into a 20 ml glass vial, sealed and incubated for 3 h 30° C. Solid-Phase Microextraction was used to extract the volatiles for the hair prior to GC-MS analysis.
Sixteen compounds were found to be important odorants in dry dog hair coat vs. 22 in wet dog hair coat. Water addition to dog hair and incubation caused substantial changes in the volatile compounds observed. Many compound groups showed increases upon water addition: strong sulfur, medicinal, or fecal smelling odors (dimethyl trisulfide, phenol, p-cresol), mushroom (1-octen-3-ol), fruity (2-nonanone), floral (â-damascenone), and earthy smelling (2,3-diethyl-5-methylpyrazine) odors, and branched or complex aldehydes (2, and 3-methyl butanal, isobutanal, 2E-octenal, acetaldehyde, benzaldehyde, phenylacetaldehyde, 2E-nonanal). Of those compounds measured, benzaldehyde, phenylaldehyde, acetaldehyde, phenol, and 2-methyl butanal showed the largest increases with 32, 6, 5, 5 and 4 times the dry hair value, respectively. Concurrent with these increases, analytical results show decreases in straight chain aldehydes upon water addition (hexanal, heptanal, and decanal). However, the changes in levels of octanal and nonanal were dog dependent. Isovaleric acid, hexanal, and heptanal showed the largest decreases upon water addition to the hair.
There are many volatile compounds which individually do not have odors associated with "dog smell", however, in combination, these compounds produce the typical "dog smell" that many people describe as unpleasant. There is a complex pattern of changes in the volatile compounds associated with wetting of brushed dog hair. This pattern appears to manifest as "wet dog" odor. While some amount of change in odor would be expected due to the different partition coefficients when water is added to the hair, the variety of differences indicates a probable chemical or biochemical reaction on the hair.