1. What Doesn’t Cause a Colour Change?
Dogs coats can change colour for various reasons, but first let’s look at what doesn’t cause this. Beet pulp has been blamed in the past because some owners have mistakenly thought that it is red in colour like beetroot whereas it is white. Dietary copper has also been accused due to copper being an orange colour in its metallic form, but it’s actually blue! It’s present at a very low proportion compared to all of the other ingredients and elements that make up commercial dog food and furthermore, doesn’t have any colour changing properties.
Hair colouration is determined by the type and amount of pigment that is deposited in the growing hair while it is in the hair follicle. Specialised pigment producing cells within the follicle secrete either a yellow-red pheomelanin or black-brown melanin. Other genetic factors affect the distribution of pigment within the hair shaft, the dilution or masking of colour, and the distribution of colour in different areas of the body. These factors account for the wide variation of hair colour seen across various breeds of dog.
3. The Most Common Causes of Changes to Coat Colour
In addition to genetics, other factors may affect the colour of the hair during either its growing or resting cycle. The most common include certain types of medication, shampoos and applications, environmental factors (e.g. sun bleaching, heat from a hair drier) and aging. As the hair reaches the end of its resting period and is ready to shed, black hairs often turn reddish. Exposure to sunlight also has an effect but generally affect variable portions of the coat, and the hair nearest the skin is generally unchanged. Colour changes resulting from external substances on the outside of the hair shaft involve the whole hair shaft, and all of the hairs in the region the substance was deposited would be affected.
4. The Physiology of Coat Growth & Colouring
A systemic factor may cause a change in colour while the hairs are still in the hair follicle, in other words a change in the pigment producing cells. Within the hair, this type of change would extend from the skin surface outwards, towards the hair tip, and the portion of the hair affected would depend on the length of time the influencing factor was in effect. For example, if the change was only in effect for 2 weeks, the colour change would appear as a band of colour on the length of the hair shaft. Because individual hairs within the coat are at different stages of development, any red colour in the coat would be dispersed throughout the coat at different levels in the hair shaft. This means that the change in colour would not be uniform and would only appear in hairs that were growing at the time the influencing factor was present. Resting hairs would not be affected.
5. Beta Carotene
Beta carotene is a precursor to vitamin A, and is an antioxidant. A very high intake of carotenoid containing foods or supplements may turn the skin orange/yellow when extra large amounts are taken. This usually affects the palms of the hands in humans. Captive flamingos are fed carotene rich foods to give them their pink colour. However, beta carotene levels in dog food should not affect the hair colour nor the skin unless further carotene rich foods are given in addition to that in the main diet.
The RDA of beta carotene for dogs is between 10,000 – 25,000 iu per day, and commercial complete dog feeds do not exceed this.
6. Porphyrin Staining
A common cause of pink stains in white or light coloured dogs is as a result of porphyrin staining. Porphyrin is a chemical found in saliva and tears, and when they dry on the coat, the colour changes from transparent to pink/red/brown. Food may be implicated in some cases since dietary allergies can result in excessive licking and / or increased tear production/salivation (but do bear in mind that increased lacrimation can also be caused by other factors including infection, atopy and eye conditions such as entropion, atopy. Eyes, muzzles, beards and the feet are most commonly affected areas by porphyrin stains.
7. Tyrosine & Phenylalanine
A study in 2002 (Biourge & Sergheraert - Red Coat Syndrome: A Dietary Cause) has shown that high levels of tyrosine and phenylalanine can affect hair pigmentation.
Tyrosine is a nonessential amino acid that is synthesized in the body from phenylalanine. As a building block for several important brain chemicals, tyrosine is needed to make epinephrine, norepinephrine, serotonin, and dopamine, all of which work to regulate mood. Tyrosine also aids in the production of melanin (pigment responsible for hair and skin color) and in the function of organs in the body responsible for making and regulating hormones, including the adrenal, thryroid, and pituitary glands. Tyrosine is also involved in the synthesis of enkephalins, substances that have pain-relieving effects in the body. Aspartame is an artificial sweetener found in many human foods and drinks which is an artificial form of phenylalanine. Whilst it is not used directly in pet foods, it could be present in some human foods and snacks if given to your dog. Tyrosine is by no means a bad thing, and some manufacturers add free tyrosine to help maintain intensive coat colour in dark breeds.
8. Prevention of “Red Coat”