Strange coat changes

Hello, hoping for some suggestions on possible investigations. My vet is at a loss. My 4 year old border collie male has had some weird coat changes on his chest in the last 6 months or so. It seems to have started after he was neutered in July but my vet thinks that’s not the cause. Essentially his once long and thick mane has become short and straggly. No change in diet. Rest of coat is the same. Coat is shiny and healthy otherwise, skin is healthy no redness or flakiness. no change in diet or anything else. Does anyone have any suggestions on what could cause this or possibly lines of investigation? 2nd pic is ‘before’

Sorry, first pic is before

Hello and Thankyou for sending both pictures.  I have to own that it is hard to make a judgement from this distance - it simply looks as though a dog has been pictured before and after a really determined brush!  Reading through your description of what you have seen however, you may be looking at coat changes due to puberty, or summer vs Winter coat in some breeds, or perhaps something like skin disease eg yeast infection, underlying endocrine disease or simply the effects of indoor vs outdoor work.  A better history and in-person examination might make it easier for your vet to judge what action, if any, is required.

Has the hair around the nose changed colour between the two pictures?   If so, yeast or saliva can sometimes be responsible for this, but again its something that your vet would need to look at at close quarters in this case.

Has the hair around the nose changed colour between the two pictures?   If so, yeast or saliva can sometimes be responsible for this, but again its something that your vet would need to look at at close quarters in this case.

Finally, despite being young and healthy, 4 years old is not too young for endocrine changes eg hypothyroidism, which can come with skin changes in some pets.

(For puberty please read neutering!)    I wonder whether your vets' pathologist has any reccommendations in this case?

They would certainly let you know whether a biopsy would be worthwhile - as a vet I sometimes find them useful people to talk to.