I have a 10 year old border collie shadow, i have just caught him eating cat poo, whether he has done this before i dont know as this is the first time i have seen him do this. Is this normal behaviour is there something he is not getting in his diet.

Most dogs will do it if given the opportunity, the same as them eating horse, goat, and sheep poo. The only thing to watch is the cat litter aspect as some cat litters aren,t good for the dog and could make them a bit poorly.