my 5yr old border collie's coat is changing from black to red and is now very coarse, it is mainly on the back and not on the sides. Does anyone know if this is significant of anything untoward?  thank you.

Has he/she been castrated/spayed?

It could be a sign on the coat dying ready for a  moult, but also coat changes (poor top coat, thinning on sides)can be a sign of under active thyroid.

Over exposure to the sun causes reddening of black hair. I had this badly in the past with one of my American Cocker Spaniels. New coat will be black again but you need to protect the coat with sunscreen spray and also persuade the dog to lie in the shade or indoors.

Dawn R.

yes, meant to say castrated at 18 months.

If it has not done this previously since he was castrated then again I'd look at Thyroid, especially if he tends to weight gain, feels the cold and is not as active as he was.  Castrated dogs are more likely to develop under active thyroid than entire ones.

As others have already mentioned the sun can cause a change in coat colour.

It doesnt affect my breed with any significance but castrating/spaying can make a huge difference in coat thickness/texture, especially when older.

Sometimes the sun can change the colour of the coat, as can moulting and also certain foods..

If all of those can be ruled out then I'd go down the medical side