This may or may not be a problem but with goats it would be. I have a calf that is 4 months old and I have noticed a bronze streak down the middle of her back. I hope photo loads for me so you can see it. If she where a goat it would be mineral deficency. What do you think?
Like goats it is caused by a copper deficiency. Copper deficiency can do the same to black cows giving them a reddish color in certain areas. Make sure you have a good mineral with ample and proper copper and it should correct itself if that is indeed the cause.