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Tyrosine supplementation and hair coat pigmentation in puppies with black coats – A pilot study

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The appearance of a red hue to the hair in black coated cats and dogs has previously been reported as a “red hair syndrome”. Such changes in hair colour are related to an alteration in the proportions of two types of pigments produced by melanocytes; black eumelanin and brown pheomelanin. In black cats, it has been demonstrated that higher levels of phenylalanine + tyrosine (Phe+Tyr) than those recommended for growth are required to support eumelanin synthesis. The purpose of this study was to evaluate if a similar observation could be made in dogs. Twelve black coated puppies (Black Labrador retrievers and Newfoundlands) were divided into 3 groups of 4 and fed 3 diets with increasing concentrations of Phe+Tyr (A: 4 g/Mcal; B: 5.8 g/Mcal; C: 7 g/Mcal) for a period of 6 months. Quantification of plasma amino acids (Phe, Tyr, Cys) and spectrocolourimetry of hair samples from the Labrador retrievers (as the a* dimension of CIE Lab system) were performed at the beginning, during and at the end of the study. There was a significant negative linear relationship between plasma Tyr levels and a* values of hair in Labrador dogs on diets A and B, suggesting that a diet with total Phe+Tyr content of 6 g/Mcal (higher than the growth recommended allowance) was necessary to ensure an optimal black coat colour in these puppies and that levels up to 7 g/Mcal can lead to a more intense black coat colour. Moreover, similar to what was found in kittens, plasma levels of Tyr up to 54 μmol/l did not guarantee an optimal black colour coat and led to the “reddish hair” appearance in black coated puppies.
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Pilot Study
Tyrosine supplementation and hair coat pigmentation in puppies with black
coats A pilot study
Adrian Watson
*, Eric Servet
, Marta Hervera
and Vincent C. Biourge
Royal Canin, Research Center, Aimargues, France
Nutrition & Endocrinology Unit, ONIRIS National College of Veterinary Medicine, Food Science and Engineering Nantes-Atlantic, 44307
Nantes Cedex 3, France
The appearance of a red hue to the hair in black coated cats and dogs has previously been reported as a red hair syndrome.
Such changes in hair colour are related to an alteration in the proportions of two types of pigments produced by melanocytes;
black eumelanin and brown pheomelanin. In black cats, it has been demonstrated that higher levels of phenylalanine + tyrosine
(Phe+Tyr) than those recommended for growth are required to support eumelanin synthesis. The purpose of this study was to
evaluate if a similar observation could be made in dogs. Twelve black coated puppies (Black Labrador retrievers and
Newfoundlands) were divided into 3 groups of 4 and fed 3 diets with increasing concentrations of Phe+Tyr (A: 4 g/Mcal;
B: 5.8 g/Mcal; C: 7 g/Mcal) for a period of 6 months. Quantication of plasma amino acids (Phe, Tyr, Cys) and spectroco-
lourimetry of hair samples from the Labrador retrievers (as the a* dimension of CIE Lab system) were performed at the begin-
ning, during and at the end of the study. There was a signicant negative linear relationship between plasma Tyr levels and a*
values of hair in Labrador dogs on diets A and B, suggesting that a diet with total Phe+Tyr content of 6 g/Mcal (higher than
the growth recommended allowance) was necessary to ensure an optimal black coat colour in these puppies and that levels up
to 7 g/Mcal can lead to a more intense black coat colour. Moreover, similar to what was found in kittens, plasma levels of Tyr
up to 54 μmol/l did not guarantee an optimal black colour coat and led to the reddish hairappearance in black coated
Keywords: dog: nutrition: black coat: red coat syndrome: tyrosine: phenylalanine: melanin: melanocytes
Melanocytes are the cells responsible for generating hair
colour. They reside within the follicle and synthesise
two types of melanin pigments, black eumelanin and
reddish-brown pheomelanin. A study by Ito (1993)
showed that, in animals, the relative proportions of
these two pigments molecules in the hair are determined
by tyrosinase activity in melanocytes. Low tyrosinase
activity results in higher proportions of pheomelanin syn-
thesis, while higher activity dictates elevated eumelanin
production. Tyrosinase activity is known to be stimulated
by tyrosine (Tyr) concentration resulting in a greater syn-
thesis of eumelanin, as shown by Slominski in 1989.In
addition, Morris et al. (2002) illustrated, using a cat
model, that the tyrosine requirement can be derived dir-
ectly from the diet or by the hydroxylation of the essen-
tial amino acid phenylalanine (Phe).
Coat reddening in cats and dogs is a phenomenon
which is capricious and poorly characterised. Yu et al.
(2001), and subsequently Morris et al. (2002), demon-
strated that if black cats were provided with diets contain-
ing reduced levels of Tyr and Phe, red coats were
observed, and also that these could be reverted to
black when cats were returned to their original commer-
cial pet food diet. Anderson et al. (2002) subsequently
conrmed that eumelanin production in black kittens
*Corresponding author:
Journal of Applied Animal Nutrition, Vol. 3; e10; page 1 of 4 doi:10.1017/jan.2015.8
© Cambridge University Press and Journal of Applied Animal Nutrition Ltd. 2015
Journal of Applied Animal Nutrition
could be compromised by a lack of Tyr and Phe in the
diet. It was estimated that the amount of these 2
amino acids required to produce a black coat was twice
as high as that required for normal growth.
The National Research Council (NRC, 2006) recom-
mend dietary levels of Tyr and Phe combined for grow-
ing dogs are 3.25 g/MCal and 2.50 g/Mcal before and
after 3 months of age, respectively. However, no data
has been published evaluating the dietary Tyr and Phe
requirements in growing dogs with respect to coat colour.
The aim of this pilot study, therefore, was to investigate
how dietary levels of Tyr can affect coat colour of grow-
ing black dogs.
Materials and Methods
The study involved 12 puppies; six female Newfoundlands
(NFL), 3 male and 3 female black Labrador retrievers. At
the beginning of the study the NFL were 3 months old and
had an average weight of 13.1 ± 0.9 kg (Mean, +/SD).
The male LR were on average 2.5 months old and weighed
8.0 ± 1.0 kg; the females were on average 3.5 months old
and also weighed 8.0 ± 0.9 kg. All of the puppies were
healthy and had homogeneous black coats. Before entering
the study, all dogs were fed with the same commercial diet
for growth of large breed puppies (Royal Canin, Maxi
Junior, Aimargues, France). For the period of the
study, all puppies were housed in the same well-ventilated,
temperature controlled indoor facility, with daily exercise
The dogs were provided with one of three experimental
diets which varied in their Tyr and Phe content (labelled
Diets A, B and C; Table 1). Diet B was a standard Royal
Canin Maxi Junior (Aimargues, France). Diets were
nutritionally complete and balanced for growth (accord-
ing NRC recommended allowances, NRC, 2006). Initial
energy requirements were calculated based on NRC
(2006). Table 1 shows proximal analyses, total Tyr, Cys
and Phe content, as well as ingredient lists for the three
diets. Other dietary amino acid contents were in excess
of NRC recommended RA for growing puppies.
Experimental design
The 12 dogs were divided into 3 groups balanced with
respect to breed and sex, whereby each contained 2
NFL, 1 male LR and 1 female LR. Each group was main-
tained on one of the three experimental diets chosen at
random and fed twice per day. The amount of diet con-
sumed by each dog was recorded daily and all dogs were
weighed weekly. Food intake was regulated such that
maximum weight gain was 0.7 kg/week for LR and
1.2 kg/week for NFL.
A heparinised blood sample was collected from each
dog 5 hours after feeding at time zero, 3 and 6 months.
Tubes were centrifuged for 15 minutes at 2000 rpm and
the plasma transferred into separate tubes. At time zero,
4 months and 6 months an 8 × 8 cm square of hair was
shaved on the right lateral area of the abdomen of all
Labrador retrievers for spectrophotometry (each time at
the same location).
Table 1. Composition of 3 diets provided to dogs in order to evaluate the effect of tyrosine intake on coat colour.
Diet A B C
Moisture 13.4 18.0 18.0
Crude Protein 89.5 92.7 94.2
Crude Fat 37.3 36.2 36.2
Total Dietary Fibre 16.3 17.7 17.7
Tyrosine total 1.5 2.4 3.8
Tyrosine free 0 0 1.6
Phenylalanine total 2.5 3.4 3.2
Phenylalanine free 0.2 0.1 0.5
Phe + Tyr total 4.0 5.8 7.0
Cystine total 0.2 0.4 0.6
Metabolisable Energy
4.1 4.0 4.0
Feed materials (in
descending order
by weight)
Corn flour, pork gelatin, beef greaves, corn,
poultry fat, beet pulp, pork fat, poultry liver
hydrolysates, mineral mix, soy oil, vitamin
mix, fish oil, d-l methionine, L-Lysine-HCl,
Beef greaves, corn flour, corn, beet pulp,
pork fat, poultry liver hydrolysates,
poultry fat, mineral mix, soy oil, vitamin
mix, fish oil
Diet C was the same that diet
B but 0.7% of crystalline
tyrosine was added during
*Calculated based on Total Dietary Fiber (NRC, 2006)
Journal of Applied Animal Nutrition
Adrian Watson et al.2
Analytical methods
Plasma was mixed with an equal volume of 0.28 mol/l
sulfosalicylic acid. The resulting precipitate was removed
by centrifugation at 16,000 g. Lithium hydroxide was
added to the supernatant to adjust pH to 2.2. Plasma
amino acid concentrations were determined by Ion
Exchange Column Chromatography (7300 Beckman
Amino Acid Analyser, Beckman Instruments, Palo
Alto, CA) on a 0.4 × 10 cm column packed with spheric-
al cation exchange resin. An equivalent of 20 µl of
plasma was injected onto the analysis column.
For the quantitative assessment of hair colour, hair
samples were analysed with a spectrocolourimeter
45/0, gloss, BYK Gardner, Brant
Industries, Germany) according to the CIE Lab colour
measurement system (Hunter Associates Laboratory,
Inc. Reston, VA, USA). Colour is determined as a
numeric value of a* (red to green axis) and b* (yellow
to blue axis). Lightness is determined as L* on a numer-
ical scale (from black = 0 to white = 100).
Data were analysed using GLMs through the MIXED
procedure of SAS v9.1.3 (SAS Institute Inc., Cary, NC,
USA). Differences were considered signicant at p 0.05.
Ethical Statement
The experimental protocol used in this study adhered to
European Union Guidelines (Ofcial Journal of the European
Communities L 358, 18/12/1986). The study was also
approved by the Royal Canin Ethics Committee (RC90).
Results and Discussion
During the study puppies gained appropriate weight and
growth/development occurred as expected for breed
norms (data not shown). There was no difference in weight
gain between dietary groups. Average daily food intakes
(+/SD) for NFL and LR were 593± 86 and 452 ± 60
g /dog /day respectively. No differences were observed
in the food intake between diet groups (p > 0.05).
Levels of Tyr, Phe and Cys in the blood of the puppies
on each diet are summarized in Table 2. There was no dif-
ference in the levels of each amino acid between the NFL
and LR within diet groups (p > 0.05). There were no sig-
nicant differences in plasma Cys and Phe between diet
groups. No changes were observed in the plasma Phe or
Cys between the different sampling points (p > 0.05).
Plasma Tyr concentrations at 3 and 6 months were signi-
cantly higher in the diet C group than the diet B and A
groups (p < 0.05). In addition, dogs fed diet B had a
higher Tyr concentration than those fed diet A (p < 0.05).
Spectrophotometric hair analysis showed no differ-
ences between groups with respect to L* and b* dimen-
sions at any of the three sampling points. There was no
difference in a* values between groups at the start of the
study and those of the Labrador puppies fed Diet C did
not change during the study. However, the a* values of
Labrador puppies fed Diets A and B had increased
Table 2. Plasma levels of tyrosine (Tyr) and cystine (Cys) of dogs consuming 3 diets with increasing Phe+Tyr content (A: 4 g/Mcal; B: 5.8 g/Mcal;
C: 7 g/Mcal) after time zero, 3 and 6 months of diet consumption. Averages are shown (± standard error) for 4 puppies.
Month Tyr Cys Phe
Initial 59.0 ± 6.38
71.5 ± 8.09
66.9 ± 6.16
34.9 ± 3.09 39.8 ± 2.39 41.3 ± 4.98 70.0 ± 5.10 74.2 ± 2.00 80.8 ± 1.70
335.1 ± 1.96
54.0 ± 1.33
79.1 ± 4.12
46.5 ± 2.35 41.3 ± 0.40 48.6 ± 1.95 71.1 ± 2.40 78.9 ± 3.20 74.9 ± 3.20
637.7 ± 2.84
53.8 ± 1.56
86.9 ± 5.20
48.2 ± 1.47 36.8 ± 3.09 42.0 ± 3.50 74.1 ± 3.40 81.8 ± 9.70 77.3 ± 4.30
different superscripts indicate significant differences of the values within a row, among groups (p <0.05);
different superscripts indicate significant differences of the values
within a column, over time (p < 0.05).
Figure 1. Changes in the a* dimension of CIE Lab index over time; three diets
with increasing Phe+Tyr (A: 4 g/Mcal; B: 5.8 g/Mcal; C: 7 g/Mcal) assessed at
time zero, 4 and 6 months of diet consumption (n = 2/diet group). Letters over
the bars denote significant differences (p < 0.05) within the same diet group
over time; *indicate significant differences among diet groups at the same sam-
pling point (p > 0.05).
Journal of Applied Animal Nutrition
Canine hair pigmentation and nutrition 3
signicantly after 4 months and did not change thereafter
(p < 0.05; Figure 1).
There was evidence of an association between plasma
Tyr concentration and the a* dimension in the Labrador
puppies. In particular, a* decreased signicantly in associ-
ation with the increased plasma Tyr seen for the group B
dogs vs group A dogs. The decrease in a* was greater
for the dogs in group C, although there was no signicance
between groups B and C. The CIE Lab method was used
by Busch-Kschiewan et al. (2004) in a study on white dogs
and permitted corroboration of what was determined visu-
ally. In humans, spectrophotometric measures have been
described as an alternative to chemical methods of asses-
sing hair eumelanin and pheomelanin variation. Shekar
et al. (2008) showed that dimension a* of CIE Lab spectro-
colourimetic index is a good approximation of pheomela-
nin concentration in hair, as it measures a continuum of the
red-green spectra. A lower a* value therefore reects a
lower hair pheomelanin concentration, manifesting as a
less reddened hair shaft.
Plasma Tyr levels were negatively correlated with a*
values in the dogs fed diets A and B (Figure 2) suggesting
a relationship between higher plasma Tyr levels and higher
eumelanin contents in the hair of black coat puppies. The
results agree with those found in kittens by Anderson et al.
(2002), where a positive correlation between plasma Tyr
levels and pyrrole-2,3,5-tricarboxylic acid was reported,
with the latter used as an indicator of eumelanin concen-
tration in the hair of cats. Raising plasma Tyr concentra-
tion from 40 to 54 μmol/L effected the most signicant
reduction in the a* dimension (Figure 2), which is similar
to previous data from cats. Increased plasma Tyr levels in
the puppies in group C did not result in a further increase
in a* values over and above group B, possibly reecting
that a point exists beyond which increasing dietary tyro-
sine has no effect, or could indeed be an artefact of our
relatively small sample sizes.
In summary, young black dogs maintained on a diet of
4 g/Mcal Phe+Tyr (diet A) showed reduced levels of
black pigmentation, even though they maintained the
normal growth trajectory and appeared healthy. Black
pigmentation was restored by increasing the Tyr content
of the diet. These initial results suggest that the nutrition-
al requirements for growth are insufcient to also meet
the demands of regular melanin synthesis, as highlighted
previously by Anderson et al. (2002) for cats. Normally,
growth is the most nutritionally demanding life stage.
Thus, a greater need for Phe+Tyr for other physiological
processes, such as hair pigmentation, may have to be
considered. Further studies to understand this relation-
ship better would be merited.
Declaration of interest
Eric Servet, Adrian Watson and Vincent Biourge are all
employees of Royal Canin SAS, Aimargues, France.
Anderson P.J., Rogers Q.R. and Morris J.G. (2002) Cats require more
dietary phenylalanine or tyrosine for melanin deposition in hair than
for maximal growth. Journal of Nutrition,132: 20372042.
Busch-Kschiewan K., Zentek J., Wortmann F.J. and Biourge V.
(2004) UV light, temperature, and humidity effects on white hair col-
our in dogs. Journal of Nutrition,134: 2053S2055S.
Ito S. (1993) High-performance liquid chromatography (HPLC) analysis
of eu- and pheomelanin in melanogenesis control. Journal of
Investigative Dermatology,100: 166S171S.
Morris J.G., Yu S. and Rogers QR. (2002) Red hair in black cats is
reversed by addition of tyrosine to the diet. Journal of Nutrition,132:
NRC (National Research Council) (2006) Nutrient Requirements of Dogs
and Cats. Washington, D.C.: The National Academies Press.
Shekar S.N., Duffy D.L., Frudakis T., Montgomery G.W., James M.
R., Sturm R.A. and Martin N.G. (2008) Spectrophotometric meth-
ods for quantifying pigmentation in human hair-inuence of MC1R
genotype and environment. Photochemistry and Photobiology,84: 719726.
Slominski A. (1989) L-tyrosine induces synthesis of melanogenesis
related proteins. Life Sciences,45: 17991803.
Yu S., Rogers Q.R. and Morris J.G. (2001) Effect of low levels of diet-
ary tyrosine on the hair colour of cats. Journal of Small Animal Practice,
42: 176180.
Figure 2. Relationship between plasma tyrosine (Tyr) levels and a* dimension
spectrocolourimetric values for the hair coat of puppies consuming 3 different
diets (A: 4 g/Mcal; B: 5.8 g/Mcal; C: 7 g/Mcal). Values of animals fed A and B
(solid line; a* = 7.6-0.09 × Tyr (μmol/l); r
= 0.98) and B and C diets showed a
closer relationship (dashed line; a* = 3.9-0.02 × Tyr (μmol/l); r
= 0.91). Each
value is the mean of two animals.
Journal of Applied Animal Nutrition
Adrian Watson et al.4
... The group also demonstrated a correlation between blood Tyr concentration and the amount of melanin found in the hair of cats. Similar work conducted in puppies showed a comparable phenomenon was present here also; Watson et al. (2015) demonstrated that, in order to enrich black pigmentation in growing Labrador retrievers and Newfoundlands, it was necessary to increase the Phe and Tyr concentration from the previously predicted requirement >3 months of 2.5 to 5.8 g/MCal. The pigmentation could be further increased when Phe þ Tyr intake was raised to 7 g/MCal. ...
... Although the primary influence on hair colouration in animals is genetic (Robinson, 1991), a number of exogenous factors are also known to exert an effect (Busch-Kschiewan et al., 2004). The evidence for a nutritional impact has been accumulating over recent times; with intake of the amino acids tyrosine, phenylalanine and cysteine, as well as copper all having been implicated in studies (Anderson et al., 2002;Watson et al., 2015Watson et al., , 2017. The black coat of certain animals is known to discolour, often showing patches of brown or reddening (Yu et al., 2001). ...
... Apart from being an aesthetic concern for breeders and owners, research into the phenomenon has suggested that it may have implications for differentiating between adequate versus optimal nutritional requirements. For example Anderson et al. (2002) for kittens and Watson et al. (2015) for puppies both highlighted that nutritional requirements for growth appear insufficient to also meet the demands of regular melanin synthesis. ...
Full-text available
Although the principle determinant of melanin derived hair colour and patterning in mammals is genetic, environmental factors are now also thought to play a role by influencing the expression of the inherited component. It has been demonstrated, for example, that the concentration of melanins deposited in the hair of cats is influenced by the amino acid composition of their diets. The observation has since been extended to dogs, whereby puppies were found to require Tyrosine intake significantly greater than that recommended for normal growth and development in order optimise melanin expression in their coat. Much of the work to date has been conducted in growing animals. These animals might, as a consequence, be considered to operate under additional nutritional strain. Less is known about the relationship between nutrition and hair melanin deposition in healthy adult animals. In this study we demonstrate for the first time that colour expression in the hair-coat of dogs is dependent on dietary intake of Tyrosine, and that the requirement appears to be in excess of the minimum level recommended to maintain health. Using spectrophotometry we were able to show that dogs fed 5.6g/Mcal Phe/Tyr showed reduced dilution of their black coat pigment compared to dogs fed 3.5g/Mcal Phe/Tyr. Specifically, following 16 weeks at the higher Tyr intake, dogs showed less yellow pigmentation to their coat (P=0.0032), and after 24 weeks at the higher intake dogs showed less red (P<0.0001) and yellow (P<0.0001), as well as greater overall dark pigmentation (P<0.0001).
... The dietary requirement of these two amino acids for maintaining a completely black coat was twice that needed to ensure normal kitten growth (Anderson, 2002). Similarly, Watson et al (2015) showed that if the concentration of total Tyr was raised from 1.5 to 2.4 g/Mcal, and total Phe from 2.5 to 3.4 g/Mcal there was a significant reduction in the degree of reddening of puppies' coat after four months of feeding, as detected by spectrophotometry. ...
... Anderson et al. (2002) then confirmed that eumelanin production in black kittens could be compromised by a lack of Phe and Tyr in the diet, with twice as much of these amino acids needed for a black coat as was required for normal growth alone. More recently this effect was replicated in dogs by Watson et al (2015), where black pigmentation was again optimised by increasing dietary Tyr/Phe over and above basic growth requirement, as detected by a reduction in the a* parameter (CIE Lab System; L* for the light-dark axis, a* the red-green axis and b* the yellowblue axis) using spectrophotometry. A link between nutrition and development of pigment in the coat of white dogs has not previously been demonstrated. ...
Full-text available
Hair colouration in animals is controlled primarily by inherited factors, with a complex set of genes and genetic variants determining phenotypic expression. The colours in the hair shaft are created initially by the melanocyte cells within the hair bulb which produce and secrete two types of melanin into the hair cortex, black eumelanin and brown pheomelanin. Together these two pigments are responsible for creating the considerable diversity of colour seen in hair across the animal kingdom. In the absence of melanins the hair remains translucent, appearing white to the eye. Colour, or absence thereof, can only be imparted on a hair during its ‘anagen’ or growing phase. During the telogen (resting) phase the colour of the hair is relatively constant, notwithstanding effects of environmental influences such as UV in sunlight, or staining agents. A further environmental factor is nutrition. The intensity of black in the hair of both cats and dogs is known to be influenced by the dietary intake of certain amino acids such as phenylalanine (Phe) and tyrosine (Tyr). However the role of nutrition in hair pigmentation is generally poorly understood. This trial investigated the impact of diet on the commonly observed red discolouration of white coat in dogs. Two panels of 13 Swiss White Shepherd dogs were fed diets containing different concentrations of Phe + Tyr (test diet containing 3.02 g/Mcal versus control 4.82 g/Mcal) and copper (test diet containing 8.93 ppm versus control 13.28 ppm) for four months. Coat colouration was assessed via spectrophotometry using the CIE Lab colour space system (International Commission on Illumination). Dogs fed the reduced Phe + Tyr and copper showed significantly less red coat pigmentation (a* parameter) by the end of the feeding study (P < 0.02). It was concluded that the level of Phe + Tyr not only affects black but also white coat in dogs. Diet can therefore exert an influence on multiple aspects of coat pigmentation.
... Overall, the EB supplement was found to increase the protein digestibility, release of lower molecular weight peptides, and free amino acids in the canine food. Previously amino acid supplementation had shown to reduce hair loss (42), induce intense and darker hair coat colors (43), and promotes normal cardiac function (44) in canines. ...
Full-text available
Digestibility and nutrient availability are important parameters when estimating the nutritional quality of pet food. We have developed a simulated semi-dynamic in vitro canine digestion model to evaluate the digestibility of dry extruded canine food. Canine food was assessed for digestible energy, dry matter digestibility, protein digestibility, non-fibrous carbohydrate (NFC) digestibility, and total antioxidant capacity (TAC) in the absence and presence of an enzyme blend (DigeSEB Super Pet). Enzyme blend supplementation in canine food was found to increase the dry matter digestibility (18.7%, p < 0.05), digestible energy (18.1%, p < 0.05), and protein digestibility (11%, p < 0.1) and reducing sugar release (106.3%, p < 0.005). The release of low molecular weight peptides (48.7%) and essential amino acids (15.6%) increased within 0.5 h of gastrointestinal digestion due to enzyme blend supplementation. Furthermore, the TAC of the digesta was also increased (8.1%, p < 0.005) in the canine food supplemented with enzyme blend. Overall, supplementation of enzyme blend in canine food is an effective strategy to enhance the food digestibility and nutrient availability for absorption.
... Although hair colour is essentially determined by genetics, nutrition can play a significant role in its expression. A number of studies have been conducted that illustrate the significant effect of nutrition on pigmentation in dogs and cats; however, the relationship between nutrition and hair pigmentation is still not well understood (Morris et al., 2002;Watson et al., 2015). ...
... A study in juvenile Labradors and Newfoundlands looked at phenylalanine and tyrosine to determine if supplementation resulted in more intense and darker coat colors. Although it was done in puppies, it likely reflected adequate eumelanin synthesis in the hair; no other physiological parameters were assessed (Watson et al. 2015). ...
Full-text available
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The dog has assumed a prominent role in human society. Associated with that status, diet choices for companion dogs have begun to reflect the personal preferences of the owners, with greater emphasis on specialty diets such as organic, vegan/vegetarian, and omission or inclusion of specific ingredients. Despite consumer preferences and many marketing strategies employed, the diets must ensure nutritional adequacy for the dog; if not, health becomes compromised, sometimes severely. The most frequent consideration of consumers and dog food manufacturers is protein source and concentration with a growing emphasis on amino acid composition and bioavailability. Amino acids in general play diverse and critical roles in the dog, with specific amino acids being essential. This review covers what is known regarding amino acids in dog nutrition.
Coat color is an obvious phenotypic characteristic. When coat color changes, it is readily observable and may be a cause for concern among veterinary clients. Some coat color changes are expected. Consider, for example, those feline breeds with color‐point coat patterns. Siamese and Tonkinese cats are born white and develop highlights of color at extremities as they age. Those unfamiliar with the breed and/or new breeders may benefit from education concerning normal development so that they have appropriate expectations. Other coat color changes, while expected, are an adverse response to medical therapy. For instance, a late effect of radiation therapy in many companion animal patients is leukotrichia, the whitening of fur in irradiated regions of the body. Other coat color changes are equally drastic, such as the stark transformation of black‐coated dogs and cats into red or rust‐brown. Some of these changes are reversible. Others, such as age‐related graying of the muzzle, are not. Most changes are strictly cosmetic; however, salivary and tear staining indicate underlying conditions that may require medical management. One cannot underestimate the importance of taking a thorough dietary history, as well as performing a comprehensive physical examination. In situations where underlying disease exists, these tools may provide clues as to the nature of the problem and what, if anything, the clinician can do to manage, if not resolve, the issue.
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In 1986, the NRC recommended a dietary concentration of 4.0 g/kg of phenylalanine and 8.5 g/kg of total aromatic amino acids for growing kittens on the basis of maximal growth rate and nitrogen balance. Black hair-coated cats were given purified diets containing the following phenylalanine + tyrosine (Phe + Tyr) concentrations (g/kg diet): 4 + 2, 4 + 4, 4 + 6, 4 + 8, 10 + 0, 10 + 2, 10 + 4, 10 + 6, 10 + 8, 10 + 10, 24 + 0 for at least 6 mo. All other amino acids were present at about twice the requirements. Total melanin and the oxidation product of eumelanin, pyrrole-2,3,5-tricarboxylic acid (PTCA) were measured in hair. There was a significant linear relationship between the concentrations of tyrosine in plasma and PTCA in hair. The relationship between PTCA concentration in hair and Phe + Tyr in the diet had a point of inflection at approximately 16 g/kg Phe + Tyr. Cats fed diets with <16 g Phe + Tyr developed "red hair." We confirmed the anecdotal reports that the black hair of cats can change from black to reddish brown. An aromatic amino acid concentration > or =18 g/kg is recommended for the prevention of visually discernible red hair in black-coated cats. Dietary concentrations >18 g total aromatic amino acids/kg diet promote a greater ratio of PTCA:total melanin in hair. We are unaware of a secondary nutrient requirement being so much greater than the requirement for growth.
In cultured amelanotic hamster melanoma cells L-tyrosine induces melanogenesis. This induction involves an increase in intracellular concentration of proteins precipitated by polyclonal anti-tyrosinase antibodies, and stimulation of the Vmax of tyrosinase activity. Therefore it is suggested that in hamster melanoma cells L-tyrosine induces synthesis of tyrosinase and melanogenesis related proteins.
Two types of melanogenesis, eumelanogenesis and pheomelanogenesis, can be switched from one type to another under certain physiologic or pathologic conditions. To study the regulation of melanogenesis, we developed a high-performance liquid chromatography method to analyze quantitatively the contents of eu- and pheomelanin in tissue samples without any isolation procedures. The rationale is that permanganate oxidation of eumelanin yields pyrrole-2,3,5-tricarboxylic acid, which may serve as a quantitatively significant indicator of eumelanin, whereas hydriodic acid hydrolysis of pheomelanin yields aminohydroxyphenylalanine as a specific indicator of pheomelanin. The method has been successfully applied to the analysis of eu- and pheomelanin not only in synthetic melanins, melanosomes, hair, feathers, and melanomas, but also in human epidermis and cultured melanocytes. These studies indicate that there exists an inverse relationship between the contents of eu- and pheomelanin. We propose that the switching between the two types of melanogenesis is mainly controlled by the level of tyrosinase activity: higher activity leads to eumelanogenesis and lower activity leads to pheomelanogenesis. When tyrosinase activity is low, dopaquinone, a reactive intermediate in melanogenesis, is quantitatively converted to glutathionyldopa, which gives rise exclusively to pheomelanin. When tyrosinase activity is high, an excess of dopaquinone is produced, which results in the inactivation of glutathione reductase and gamma-glutamyl transpeptidase, enzymes essential for pheomelanogenesis. These biochemical events eventually leads to eumelanogenesis.
Experiments were conducted to investigate the basis for the change in hair colour of black cats to reddish-brown. Black cats were given purified diets based on gelatin, casein plus lactalbumin, or crystalline amino acids as protein sources. Diets that caused the colour of hair to change to reddish-brown were associated with a reduction in melanin in hair (observed by direct microscopic examination), a decreased total melanin concentration and low concentrations of tyrosine in plasma. Reddish hair coat was induced in black kittens born to queens given a tyrosine-deficient diet during pregnancy. Black hair colour was maintained or restored by diets containing a high concentration of tyrosine or phenylalanine. Current dietary recommendations for dietary tyrosine and phenylalanine for cats are below those required to support maximal melanin synthesis in black cats. The requirement appears to be greater than a combination of 4.5 g tyrosine plus 12 g phenylalanine/kg diet but less than 24 g phenylalanine alone/kg diet.
Eumelanin (brown/black melanin) and pheomelanin (red/yellow melanin) in human hair can be quantified using chemical methods or approximated using spectrophotometric methods. Chemical methods consume greater resources, making them less attractive for epidemiological studies. This investigation sought to identify the spectrophotometric measures that best explain the light-dark continuum of hair color and the measure that is best able to distinguish red hair from nonred hair. Genetic analysis was performed on these two measures to determine the proportion of genetic and environmental influences on variation in these traits. Reflectance curves along the visible spectrum and subjective ratings of hair color were collected from 1730 adolescent twin individuals. Discriminant class analyses were performed to determine the spectrophotometric measure that could best proxy for eumelanin and pheomelanin quantities. The ratio of light reflected in the green portion of the spectrum to that reflected in the red portion of the spectrum was best able to distinguish red hair from nonred hair. Melanocortin 1 receptor (MC1R) genotype explained some, but not all, variation in this measure. Light absorbed in the red portion of the spectrum was best able to explain the light-dark continuum of hair color. Variance components analysis showed that there were qualitatively different genetic influences between males and females for the light-dark continuum of hair. Our results show that spectrophotometric measures approximating variation in eumelanin and pheomelanin may be considered as an alternative to chemical methods in larger epidemiological studies.