MANY groomers ask me why terrier or terrier mix breeds become fine and lackluster in color as they grow out from clippering.
Harsh guard coat that is actively growing has the highest concentration of pigment deposit.
The more harsh the texture, the more pigment will reside within the hair shaft.￼
Melanin (pigment) granules reside deep in the hair shaft along the cortex and beneath the cortical fibrils.
Hair in a resting phase will not be as harshly textured or deeply pigmented as a actively (anagen) phase hair￼￼￼￼.
When you clip hair off above the skin, that only removes the length of coat which is visible to us.￼￼
What’s still seated in the hair follicle cup is the remaining length of the hair shaft.
As the hair moves into a resting (catagen) phase, the pigment is lessened drastically as is the thickness and texture because the hair is no longer actively growing.
As this hair is slowly pushed up in the follicle cup it will be fine (having a thinner and more porous cuticle), be poorly colored (lackluster), and usually doesn’t reflect light very well or have gloss/shine.￼
As well, repeated clippering of haircoat from long to short also sit in the stratum corny him layer of skin. Thicker skin produces finer/thinner hair￼.
And as a final consideration, dogs of the Terrier class cycle through coat differently than any other breed class.￼ They do not produce actively growing hair from deeper within the follicle until the resting or dormant phases are adequately removed.￼
There are a few more facets of this considering hormone/endocrine changes, underlying medical conditions, side effects from medications, the dog’s overall health and being able to maintain core temperature & skin oil/moisture levels, secondary microflora imbalances of the skin’s microbiome, etc.
But, to get from point A to point B this is the simplest route of general insight into this phenomenon.￼