A Border Collie's black coat turning reddish-brown often indicates a disruption in melanin production, frequently stemming from nutritional deficiencies. Addressing this involves supplementing your dog's diet with essential nutrients.
Firstly, impaired melanin production, such as reduced activity of tyrosinase, is a key factor. For dogs without underlying genetic conditions, this is primarily linked to nutritional deficiencies. Any factor that hinders nutrient supply to the hair papilla can affect melanin production, thus impacting coat color. This includes a lack of essential vitamins like A, B1, B2, B6, and B12, as well as folic acid and minerals such as calcium, zinc, and iron. Supplementing with trace minerals (particularly copper and zinc) and vitamin-rich foods is recommended. Additionally, psychological stress and other neuroendocrine imbalances can interfere with the growth and development of melanocytes in the hair papilla and bulb, impairing their ability to produce melanin. This disrupts the formation of melanin granules.
Secondly, the degradation of melanin can also cause the coat to lose its black color. While sun exposure can darken the skin, it does not darken the coat. Excessive ultraviolet (UV) radiation can cause hair to lose moisture, leading to dryness, lack of elasticity, static, and breakage. Moreover, UV radiation can break down the protein chains within the hair (melanin granules are proteins), creating pores in the hair fibers. This results in the gradual fading and reduction of melanin, causing the coat to lose its shine and luster. The cuticles lift and flake off, resulting in a coarse, dull, and yellowed coat.