OBJECTIVES
There are reports from breeders that coat color of dogs changed from black to reddish brown when fed certain commercial pet foods. Until recently, this "Red Coat Syndrome" has been considered as anecdotal and unfounded. Lately, it has been reported that levels of tyrosine (Tyr) and phenylalanine (Phe) required to support maximal melanin synthesis in cats were above current recommendations for growth.(Yu et al. 2001, Morris et al. 2001) The purpose of this study was to evaluate if a similar observation could be made in dogs.
MATERIALS
Twelve black puppies (6 Newfoundlands, 6 Labradors) were weaned on a large breed commercial puppy diet. They were then divided in 3 groups matched for breed and sex, fed 3 diets with similar guarantee analysis (A,B,C) but with levels of Phe+Tyr in diet A = 1.9 and diet B = 2.6 times the requirements recommended for growth by the American Association of Feed Control Official (AAFCO). Diet C was Diet B coated with free Tyr so to reach 3.2 times AAFCO requirements. Food intake, bodyweight and coat color were monitored for a year. Hair samples were collected monthly, pictures taken bimonthly and plasma samples for amino acid profiles every 3 months.
RESULTS
Dogs remained healthy and showed similar growth patterns on the 3 diets. After 2 months, hair growth on diet A was red and on diet C darker than on diet B. After 5 months, the coat of dogs fed diet A appeared reddish brown, and it was possible to recognize blindly between dogs fed diet B or C based on the intensity of black. Over the growth, plasma tyrosine dropped in dogs fed diet A and B whereas it raised in dogs fed diet C supplemented with free Tyr.
CONCLUSION
In dogs, diet can affect hair pigmentation and could explain the "red coat syndrome" reported by breeders. Addition of free available Tyr to the food can prevent the "Red hair syndrome" and optimize hair pigmentation, even for diets that have a level of Phe+Tyr above current recommendations.
References
1. Yu S et al. Effect of low levels of dietary tyrosine on the hair colour of cats. J Small Animal Practice, 2001 :42,176-180.
2. Morris JG et al. « Red hair » in Black cats is reversed by addition of tyrosine to the diet. Proceeding of Waltham Symposium, 2001 :26