All rough's moult at least once a year, and not all at the same time - unspayed bitches sometimes twice dependant on their heat cycle. I usually find it is four months to come out and four months to grow back! But quickest way to get it out is to bath the dog, dry it with hairdryer and you will get majority of the undercoat out in one go, but be warned that for the next week or so it will be everywhere, just keep brushing! I have one that is starting to moult, and one that is just coming back into coat, unfortunately the one that is moulting is entered at Crufts in March! You could also try giving the dog Restore, or some other coat product to bring the coat back into condition.