My almost 5 year old greyhound has been lame since March and has been diagnosed by a greyhound vet as having no fat in his pads, making walking on anything that is not silky smooth uncomfortable.
I have tried various boots but his skin is so thin he ends up with open sores on the tops and sides of his feet.  His bodily condition is excellent and he has no trouble holding weight and eats well.
Can anyone give me any info on this condition?  What causes it? etc etc as I can't find anything by googling.

It will be part of his makeup/in breeding. Greyhounds/whippets need thick pads to deal with their purpose/what they were originally bred to do. There is very little you can do, apart from try what you have been. You might like to try excercising him on sand, it may help as it is a soft surface for him to excercise on...road walks will be virtually a no no, field work/walking will be the hardest his feet will cope with.

> It will be part of his makeup/in breeding.

He seems to have only developed this in his 6th year though. Is that something that commonly occurs in the breed?  What is it that makes the feet deteriorate later on in life?

The op says he is nearly 5 but no there should be no deteriation thoughout the life of a hound.
I am only guessing but no it should not be common in the breed..it certainly isnt in Whippets. It does seem odd for it to happen now...if he hasnt got thick pads now he probably never had them in earlier life..just a stab in the dark here but maybe he is getting heavier as he is maturing & it is only now its becoming a problem.

> ...if he hasnt got thick pads now he probably never had them in earlier life..

I see.  Yes, I meant to type 5th year :)

> just a stab in the dark here but maybe he is getting heavier as he is maturing & it is only now its becoming a problem.

So, would it be fair to say Greyhounds suffering from this condition would best be kept on the lean side?

> You might like to try excercising him on sand, it may help as it is a soft surface for him to excercise on

Wouldn't the friction of his pads moving tend to rub............think sandpaper!

>> You might like to try excercising him on sand, it may help as it is a soft surface for him to excercise on
> Wouldn't the friction of his pads moving tend to rub............think sandpaper!

No, it isnt the same

I went on holiday to a beach with my dogs who had perfectly healthy pads. Two days of walks on the beach left them very sore and almost raw. I would be very careful about walking a dog on sand with pad problems

I've certainly found that a few days on the beach in spring remove all the winter's hard skin from my feet ( I know, too much information !!)

Have a look at https://www.neopaws.com/catalog/dogshoesdogbootsandlegwraps-c-39.html they also do gel insoles for the boots for extra protection, I used to use these for one of dogs and found them to be hard wearing, easy to take on and off, and most importantly, didn't come off when the dog ran.

I only have to walk barefoot in sand, for the friction to badly blister my feet. 

Although I do take dogs on the beach, I have a bowl of warm water ready to rinse feet off.  I wouldn't do it if I had dogs with a known problem with the paws.

Sand?

Depends on the beach, and on the tide to some degree.  We have beaches near us that are Severn Estuary mud/sand and they provide a good firm surface for walking on - a bit of 'give' but no grain separation.  We only have to walk for a very short distance on the more usual soft, bright, dry sand to reach miles of good hiking surface.

When we were in France recently we visited an Atlantic Coast beach with beautiful sand dunes.  Great to look at but a complete bugger to walk on.  I know what you mean about polishing dry skin!!  Luckily it was just us, no dogs, and no one around to watch me flail about on the soft surface or squeal due to the heat on my bare feet :)