History

Dog Skin and Coat

Key Message

WALTHAM has contributed to the understanding of the effect of nutrition on skin health and coat appearance in dogs by:

  • Validating a non-invasive system for measuring canine trans-epidermal water loss.
  • Developing a sensory evaluation panel of people trained to detect differences in the appearance of dogs’ coats.
  • Identifying the dietary levels of zinc and linoleic acid that improve skin and coat condition in dogs.
  • Demonstrating that a diet supplemented with pantothenate, choline, nicotinamide, histidine and inositol significantly decreases trans-epidermal water loss in dogs.
  • Generating insights into;
           a.    The beneficial effect of aloe vera, curcumin, vitamin C and taurine on in vitro canine fibroblast (structural cells) migration and keratinocyte (skin cell) barrier function.
           b.    The beneficial effect of dietary biotin and other B vitamins on skin and coat appearance.

Background

The skin forms a protective outer layer, providing a barrier against potentially harmful physical, chemical and microbial external factors. The skin also prevents water loss, stores nutrients and is involved in sensory perception and thermoregulation. Unlike humans, vitamin D synthesis does not occur in the skin of dogs so a dietary source is required. The health of the skin and coat may become compromised during times of nutritional deficiency, imbalance or excess and as a result of allergic dermatitis (atopy). Canine skin disease represents one of the most common reasons for a dog to visit the vet, comprising 27% of in-patients in a USA study (Lund 2011). The skin of dogs (Lloyd and Garthwaite 1982) is thin compared with humans, making them susceptible to skin complaints. Dogs can also be afflicted by a variety of diseases that affect the skin and coat. For example, dogs with atopic dermatitis experience pruritus (itching) (Griffin and DeBoer 2001) that can be intense and may result in skin trauma and hair loss due to scratching. Atopic dermatitis may be associated with allergies. Fleas are frequently involved (Scheidt 1988; Sousa and Halliwell 2001), with food-related (Hillier and Griffin 2001) and environmental (Hill and DeBoer 2001) allergens also implicated. Dogs with atopic dermatitis may have a skin barrier defect, with higher trans-epidermal water loss (Olivry 2011).

Dietary zinc is an important nutrient involved in healthy development of the skin and coat. Zinc is a component of a wide range of metalloenzymes and as a co-factor for RNA and DNA polymerases its presence is of particular importance in the rapidly-dividing epidermis (Watson 1998). Zinc is also essential for fatty acid synthesis and participates in inflammation and immune reactions (Watson 1998). Zinc deficiency in dogs manifests primarily in the skin with erythema, alopecia, crust and scale (Colombini 1999). Food ingredients and nutrients such as aloe vera, curcumin, vitamin C and taurine have a variety of anti-inflammatory and antioxidant activities (see Fray et al. 2004) that might be beneficial for the skin.

Linoleic acid is also important for skin and coat condition. Dogs are unable to synthesise this fatty acid so a dietary source is essential. Fatty acids are important for maintaining cell membrane fluidity and the cutaneous water permeability barrier (Campbell 1990; Watson 1998). Linoleic acid deficiency in growing dogs manifests as coarse, dry hair and thickened and oedematous skin (Hansen et al. 1954; Wiese et al. 1966). A wide range of other nutrients, including B vitamins, also have a role in barrier function (Watson et al. 2006).

Why WALTHAM is Interested

Enhancing skin and coat condition is good for the dog, since the skin helps protect against dehydration, pathogens and environmental temperature changes. For the owner, their dog’s skin and coat condition is important both aesthetically and as a key indicator of nutritional adequacy and health. Dogs with atopic dermatitis might particularly benefit from dietary support.

Approach

Firstly, non-invasive ways of measuring skin health and assessing coat quality were developed. Then, the benefits of dietary supplementation were investigated, including zinc and linoleic acid, and a combination of pantothenate, choline, nicotinamide, histidine and inositol. Other studies investigated the effect of biotin and other B vitamins, or a combination of aloe vera, curcumin, vitamin C and taurine.

Capability Development (Measurement of Trans-Epidermal Water Loss)

WALTHAM validated a non-invasive system for measuring trans-epidermal water loss in the dog.

Trans-epidermal water loss (TEWL) is the loss of water through the epidermis by passive diffusion. It is a normal, constantly-occurring physiological process, but when excessive it can result in dehydration of the skin and compromised barrier function. Measurement of TEWL is widely used for the assessment of barrier function in humans but data in dogs were limited.

In a study at WALTHAM the technique for non-invasively measuring TEWL was validated for dogs (Watson et al. 2002). The measurement involves parting the hair and placing a probe against the dog’s skin for 45 seconds whilst the machine takes a reading.

A requirement for the dog to be completely still during measurements (including the tail) was a pre-requisite in order to minimise variation in the data and enable the number of dogs in the study to be optimised. This was achieved using positive reward-based (clicker) training during the preceding weeks. Untrained dogs produced readings 47% greater than trained dogs (Figures 1 Watson et al. 2002). The likelihood is that training the dogs to remain still during measurements reduced air movement, minimising this known source of variation when assessing TEWL. 

Other factors affecting the results were also identified, with shaving the hair decreasing TEWL (Figures 1), older age tending to increase it (Figures 1), and variations evident between different anatomical sites (Watson et al. 2002).

Dog Skin and Coat Shaved and Unshaved WDC19
Reproduced from Watson A, Fray T, Clarke S, Yates D, Markwell P. Reliable use of the ServoMed Evaporimeter EP-2 to assess transepidermal water loss in the canine. J Nutr. 2002 Jun;132(6 Supp 2):1661S-1664S

Dog Skin and Coat Age
Reproduced from Watson A, Fray T, Clarke S, Yates D, Markwell P. Reliable use of the ServoMed Evaporimeter EP-2 to assess transepidermal water loss in the canine. J Nutr. 2002 Jun;132(6 Supp 2):1661S-1664S

Dog Skin and Coat Tained and Untrained
Reproduced from Watson A, Fray T, Clarke S, Yates D, Markwell P. Reliable use of the ServoMed Evaporimeter EP-2 to assess transepidermal water loss in the canine. J Nutr. 2002 Jun;132(6 Supp 2):1661S-1664S

Figure 1: Effect of training, age, and shaving on TEWL (Watson et al. 2002)

Capability Development (Assessors)

A trained sensory evaluation panel can detect differences in the appearance of dogs’ coats 

The appearance of a dog’s coat is of importance to the owner because it is considered to reflect the dog’s state of health and wellbeing and the nutritional quality of the diet. However, devising ways to measure this subjective quality requires breadth of thinking. The human hair care industry commonly uses a sensory evaluation panel to assess product performance, and this concept was adopted by WALTHAM.

A panel of assessors were trained to detect differences in:
•    Gloss – the amount of light reflected from the coat, assessed visually without touching the dog.
•    Softness – by running the fingers through the coat.
•    Optimum coat feel – the absence of a greasy or dry feel to the coat.
•    Scale or dander – assessed in three areas by lifting the hair and examining the hair and the skin.

Each was scored on a 9-point scale from 1 (coat in poor condition) to 5 (coat in good condition), with half scores discernible (Marsh et al. 2000).

Black Labrador retrievers are used for the majority of skin and coat work as early in the programme their coat colour and type was found to be well-suited for the human panel to detect differences in sensory attributes.

Discovery (Appearance and Aesthetics)

The addition of zinc and linoleic acid above lower levels defined for a complete and balanced diet can improve coat condition in dogs

In collaboration with De Montfort University, Lincolnshire, UK, WALTHAM investigated the effects of supplementing a nutritionally-complete and balanced diet with zinc (overall 23.9 mg/MJ) and linoleic acid (overall 3.6 g/MJ) (Marsh et al. 2000). A total of 32 healthy adult dogs were allocated to one of four dietary regimens, all of which started with a 9-week unsupplemented pre-feed phase. For the 9 weeks following this, the four panels of dogs were fed the diet alone, or diet supplemented with zinc, linoleic acid, or zinc plus linoleic acid. Skin and coat assessments took place at the end of the pre-feed and the end of the test phases, using sensory evaluation and trans-epidermal water loss (TEWL).

Supplementation of the diet with both zinc and linoleic acid produced significant improvements in coat gloss (P=0.05) and scale (P=0.0007) compared with the control group (Figure 2). There was no significant effect of either zinc or linoleic acid alone on gloss or scale. There were no significant changes in coat softness and optimum coat feel as a result of supplementation with zinc and/or linoleic acid (Marsh et al. 2000). TEWL decreased significantly during the study in all three supplemented groups (P=0.05 Figure 3), but the difference between groups and versus control failed to reach significance (Marsh et al. 2000).

Dog Skin and Coat Chemicals
Reproduced from Marsh KA, Ruedisueli FL, Coe SL, Watson TDG. Effects of zinc and linoleic acid supplementation on the skin and coat quality of dogs receiving a complete and balanced diet. Vet Derm. 2000.11;277-284 Blackwell Publishing, European Society of Veterinary Dermatology, American College of Veterinary Dermatology.The definitive version is available at www.blackwell-synergy.com

Dog Skin and Coat
Reproduced from Marsh KA, Ruedisueli FL, Coe SL, Watson TDG. Effects of zinc and linoleic acid supplementation on the skin and coat quality of dogs receiving a complete and balanced diet. Vet Derm. 2000.11;277-284 Blackwell Publishing, European Society of Veterinary Dermatology, American College of Veterinary Dermatology.The definitive version is available at www.blackwell-synergy.com

Figure 2: Change in coat gloss and scale with zinc and linoleic acid (Marsh et al. 2000). Bars represent the numerical difference between the mean of duplicate observations at the end of the test phase and the end of the pre-feed. * denotes significant difference compared with control group (P?0.05, one-way ANOVA)

Dog Skin and Coat transepidermal
Reproduced from Marsh KA, Ruedisueli FL, Coe SL, Watson TDG. Effects of zinc and linoleic acid supplementation on the skin and coat quality of dogs receiving a complete and balanced diet. Vet Derm. 2000.11;277-284 Blackwell Publishing, European Society of Veterinary Dermatology, American College of Veterinary Dermatology.The definitive version is available at www.blackwell-synergy.com

Figure 3: Change in TEWL with zinc and linoleic acid (Marsh et al. 2000). * denotes significant difference compared with pre-feed values (P=0.05)

This study shows that the addition of zinc and linoleic acid above specifically defined levels to a complete and balanced diet can improve coat condition in dogs.

Discovery (Health Maintenance and Disease Prevention)

A diet supplemented with pantothenate, choline, nicotinamide, histidine and inositol significantly decreases trans-epidermal water loss in dogs

The epidermis of the skin barrier is composed of two main parts, the cells or corneocytes and the intercellular lamellar lipid. The epidermal lamellar lipid comprises mainly ceramides, sterols and fatty acids. A series of studies at WALTHAM investigated if nutrients could be used to improve the epidermal barrier (Watson et al. 2006).

Firstly, 27 nutritional components were screened in vitro for their ability to up-regulate epidermal lipid synthesis, using cultured canine keratinocytes (Watson et al. 2006). Next, seven of the 27 components (pantothenate, choline, nicotinamide, histidine, proline, pyridoxine and inositol) were retested using an in vitro trans-epidermal diffusion experimental model, providing a functional assessment of barrier properties (Watson et al. 2006). The 5 best-performing nutrients were pantothenate, choline, nicotinamide, histidine and inositol (Watson et al. 2006).

Following these in vitro studies, the 5 best-performing nutrients were fed to 32 healthy adult dogs and skin health assessed (Watson et al. 2006). The dogs all received an 8-week pre-feed of a nutritionally complete and balanced diet. For the next 12 weeks, half continued on this diet, while the other half received the diet supplemented with a combination of pantothenate, choline, nicotinamide, histidine and inositol. Barrier function was measured throughout using trans-epidermal water loss (TEWL).

No effect was evident at 3 or 6 weeks, but at 9 weeks and 12 weeks the dogs fed the supplemented diet showed significant reductions in TEWL compared with their values at the end of the pre-feed phase (Watson et al. 2006). In the control group, there was no significant change in TEWL at any time point compared with the end of the pre-feed (Figure 4 Watson et al. 2006). In the control group, there was no significant change in TEWL at any time point compared with the end of the pre-feed (Watson et al. 2006).

Dog Skin and Coat TEWL measurments
Reproduced from Watson AL, Fray TR, Bailey J, Baker CB, Beyer SA, Markwell PJ. Dietary constituents are able to play a beneficial role in canine epidermal barrier function. Exp Dermatol. 2006 Jan;15(1):74-81

Figure 4: A diet supplemented with pantothenate, choline, nicotinamide, histidine, and inositol significantly decreased TEWL at 9 and 12 weeks in dogs (Watson et al. 2006). On x-axis, SOP = start of pre-feed, EOP = end of pre-feed, then weeks 3, 6, 9 and 12. Each time-point was compared with EOP for that group of dogs. * P<0.05, ** P<0.01 (Kruskal-Wallis)

This study showed that a combination of pantothenate, choline, nicotinamide, histidine and inositol, when fed at supplemented concentrations, significantly reduced TEWL in dogs after 9 weeks.

Insight Generation (Disease Management)

A combination of aloe vera, curcumin, vitamin C and taurine has a beneficial effect on in vitro canine fibroblast migration and keratinocyte barrier function

Aloe vera, curcumin, vitamin C and taurine have a variety of anti-inflammatory and antioxidant activities (see Fray et al. 2004) that might be beneficial in the skin.

In this study, the potential for the combination of aloe vera, curcumin, vitamin C and taurine to affect the migration of canine ?broblasts and the permeability of canine keratinocytes was assessed in vitro (Fray et al. 2004). Migration of fibroblasts is important for skin repair, whilst keratinocytes form the outer layer of the skin’s barrier.

The fibroblast migration assay assessed the ability of cultured fibroblasts to migrate over a line drawn on their dish (representing a wound edge). The migration of canine dermal ?broblasts treated with the combination of aloe vera, curcumin, taurine and vitamin C was signi?cantly greater (P<0.05) than untreated cells (Figure 5 Fray et al. 2004).

The keratinocyte permeability assay measured the diffusion of labelled water through a cultured keratinocyte sheet. The diffusion of tritiated water across canine keratinocyte cells was signi?cantly less (P<0.05) for those cells treated with the combination of aloe vera, curcumin, taurine and vitamin C than for untreated cells (Figure 6 Fray et al. 2004).

Dog Skin and Coat
Reproduced from Fray TR, Watson AL, Croft JM, Baker CD, Bailey J, Sirel N, Tobias A, Markwell PJ. A combination of aloe vera, curcumin, vitamin c and taurine increases canine fibroblast migration and decreases tritiated water diffusion across canine keratinocytes in vitro. J Nutr. 2004 Aug;134(8Supp);2117S-2119S

Dog Skin and Coat Diffusion of Tritiatied
Reproduced from Fray TR, Watson AL, Croft JM, Baker CD, Bailey J, Sirel N, Tobias A, Markwell PJ. A combination of aloe vera, curcumin, vitamin c and taurine increases canine fibroblast migration and decreases tritiated water diffusion across canine keratinocytes in vitro. J Nutr. 2004 Aug;134(8Supp);2117S-2119S

Figure 5 & 6: Effect of the combination of aloe vera, curcumin, taurine, and vitamin C on canine fibroblast migration and keratinocyte permeability (Fray et al. 2004). Different letters denote significant difference (P<0.05, Student-Newman-Keuls test) for incubation with (solid bar) or without (open bar) the nutrient combination

Insight Generation (Appearance and Aesthetics)

Dietary biotin and other B vitamins are associated with improvements in skin and coat appearance

In a study at WALTHAM the dietary levels of B vitamins (biotin, riboflavin, niacin, pantothenic acid and pyridoxine) associated with an improvement in skin and coat appearance were identified in black Labrador retrievers.

After a 9-week pre-feed phase, 8 dogs were fed a commercially-available, nutritionally complete diet supplemented with biotin and other B vitamins for 9 weeks while 8 dogs received the same diet un-supplemented (Marsh et al. 1999). The effects of diet were assessed by a trained sensory evaluation panel.

A significant (P<0.05) improvement in coat feel and softness was seen compared with controls (Figure 7 Marsh et al. 1999). A significant (P=0.005) reduction in coat scale was also observed compared with controls (Figure 8 Marsh et al. 1999).

This study showed that supplementation of a nutritionally complete diet with specific nutrients can enhance the coat condition of dogs.

Dog Skin and Coat change in Coat Scale
Reproduced from Marsh KA. WALTHAM Focus, Focus on Skin and Coat Special Edition 1999 Apr; 29-30

Dog Skin and Coat Change in Coat softness
Reproduced from Marsh KA. WALTHAM Focus, Focus on Skin and Coat Special Edition 1999 Apr; 29-30

Figure 7 & 8: Improvement in coat softness and coat scale in dogs receiving biotin and other B vitamins (Marsh et al. 1999). Note that a positive score indicates a reduction in the amount of scale on the coat i.e. an improvement in the attribute of coat scale

References

Campbell KL. Fatty acid supplementation and skin disease. Vet Clin North Am Small Anim Pract. 1990 Nov;20(6):1475-86.


Colombini S. Canine zinc-responsive dermatosis. Vet Clin North Am Small Anim Pract. 1999 Nov;29(6):1373-83.


Fray TR, Watson AL, Croft JM, Baker CD, Bailey J, Sirel N, Tobias A, Markwell PJ. A combination of aloe vera, curcumin, vitamin C, and taurine increases canine fibroblast migration and decreases tritiated water diffusion across canine keratinocytes in vitro. J Nutr. 2004 Aug;134(8 Suppl):2117S-2119S.


Griffin CE, DeBoer DJ. The ACVD task force on canine atopic dermatitis (XIV): clinical manifestations of canine atopic dermatitis. Vet Immunol Immunopathol. 2001 Sep 20;81(3-4):255-69.


Hansen AE, Sinclair JG, Wiese HF. Sequence of histologic changes in skin of dogs in relation to dietary fat. J Nutr. 1954 Apr 10;52(4):541-54.


Hill PB, DeBoer DJ. The ACVD task force on canine atopic dermatitis (IV): environmental allergens. Vet Immunol Immunopathol. 2001 Sep 20;81(3-4):169-86.


Hillier A, Griffin CE. The ACVD task force on canine atopic dermatitis (X): is there a relationship between canine atopic dermatitis and cutaneous adverse food reactions? Vet Immunol Immunopathol. 2001 Sep 20;81(3-4):227-31.


Lloyd DH, Garthwaite G. Epidermal structure and surface topography of canine skin. Res Vet Sci. 1982 Jul;33(1):99-104.


Lund E. Epidemiology of atopic dermatitis. Vet Focus. 2011;21(3):32-33.


Marsh KA, Ruedisueli FL, Coe SL., Watson TDG. Effects of zinc and linoleic acid supplementation on the skin and coat quality of dogs receiving a complete and balanced diet. Vet Derm. 2000;11:277-284.


Marsh KA. Improving the coat condition of dogs. WALTHAM Focus, Focus on Skin and Coat Special Edition. 1999:29-30.


Olivry T. Is the skin barrier abnormal in dogs with atopic dermatitis? Vet Immunol Immunopathol. 2011 Nov 15;144(1-2):11-6.


Scheidt VJ. Flea allergy dermatitis. Vet Clin North Am Small Anim Pract. 1988 Sep;18(5):1023-42.


Sousa CA, Halliwell RE. The ACVD task force on canine atopic dermatitis (XI): the relationship between arthropod hypersensitivity and atopic dermatitis in the dog. Vet Immunol Immunopathol. 2001 Sep 20;81(3-4):233-7.


Watson AL, Fray TR, Bailey J, Baker CB, Beyer SA, Markwell PJ. Dietary constituents are able to play a beneficial role in canine epidermal barrier function. Exp Dermatol. 2006 Jan;15(1):74-81.


Watson AL, Fray TR, Bailey J, Baker CB, Beyer SA, Markwell PJ. Dietary constituents are able to play a beneficial role in canine epidermal barrier function. Exp Dermatol. 2006 Jan;15(1):74-81.


Watson A, Fray T, Clarke S, Yates D, Markwell P. Reliable use of the ServoMed Evaporimeter EP-2 to assess transepidermal water loss in the canine. J Nutr. 2002 Jun;132(6 Suppl 2):1661S-4S.


Watson TD. Diet and skin disease in dogs and cats. J Nutr. 1998 Dec;128(12 Suppl):2783S-2789S.


Wiese HF, Yamanaka W, Coon E, Barber S. Skin lipids of puppies as affected by kind and amount of dietary fat. J Nutr. 1966 May;89(1):113-22.

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