loss of pigment in coat

My 5 month old Newfoundland is getting her adult coat in.  Her puppy coat is light brown and her adult coat is coming in a bit darker but with white.  Her tail looks almost like a raccoon tail because it is "bands" of color.  My breeder said that a loss of pigment in a coat is a deficiency in something.  A protein maybe?  She was on 28% protein Nutrochoice for three months.  I switcher her to 23% protein for the last 2 months and I think that is when it may have started.

[Ghilly]

That little bit of difference in protein should in no way make a difference of that degree in coat color.  A dog would have to be severely malnourished in order to have coat color be affected that severely and even then I don't know that it would change that much.

It sounds to me more like a genetic thing going on.  There is a dilution gene that might be coming into play here that I would suspect is more likely to be responsible for this.  There are only a handful of breeds that are affected by the dilution gene, and the Newfoundland is one such breed.  The dilution gene affects eumelanin, a pigment responsible for the black color, and phaeomelanin, a pigment responsible for brown colors.   The resulting color of a dilution in the brown gene is a color called Isabella, which is a creamy tan/almost whitish color.  My guess would be that your puppy is completely healthy but is displaying the dilute brown, or Isabella color pattern now that her puppy coat is shedding out and her adult coat is coming in.  Do you have any pics you can post?

Ghilly

[Margot49]

Completely agree with Ghilly. Sounds like a genetic issue to me also.  
Have you contacted the breeder about this?  If they are a good breeder, they should be familiar with their dogs and the dogs of the dam/stud used.  
I don't know why the breeder would say it was a deficiency in something.  Years ago, when I had Shelties some of us started noticing our black dogs getting a red tinge to the black. We figured out it was the food we were feeding that had beet pulp in it.  But, that affected the entire coat, not what you are describing. There was no pattern.