Hi my bitch has a litter of pups and they are loverly, they are 5 weeks old. The thing is they bite each other really hard when thier playing, i  read this is normal and i shouldnt interfear is this true.  

Absolutely sammye, it is what puppy siblings do and completely normal.

Their fighting will get more and more vocal and you will find they gang up on each other and pull each other around by ears, necks, tails :-D

Allow them to enjoy their games and play.

Also some will be more dominant than others, I usually find it to be the bitches, by 8 weeks, (which is when I personally home my pups) you will also feel it time as the inner fighting does get rough, throw in lots of toys and tugs for them to play with it will detract them from doing this to each other as much.

My Mums always sort the pups out from getting too rough.

I had two pups in my last litter who started fighting in earnest at 8 weeks +. One of them I was keeping and the other one had been returned after three days from what should have been an excellent home! (their child 8yrs, although having grown up with large guarding breed and visited the litter a few times, didn't like the puppy jumping up or mouthing).
I had to keep them separated after a few visits to the vet for abcesses and a 'heamatoma' sp? on the shoulder from their fighting. Once they had latched on to each other, they would not let go  regardless of anything, mum, a bucket of cold water, using a loud noise etc
The returned pup has since gone to a new home locally, but when they meet up they still have 'issues' which has caused a great amount of 'fun' when attending puppy training classes (which also includes two of their litter mates who don't have any interest in fighting with either of these)

I know that in some terrier brees fighting among pups can be for real, but certainly thsi woudl be rare in most breeds?

I'd be very concerned about the temperament of pups who were doing enough damage to require vet treatment at such a young age.

That would be my reaction too.  I wouldn't expect fighting among pups under a year of age even males that didn't know each other, and never bitches.

I've never heard of such young pups fighting in earnest and causing such harm to each other What breed do you have MudMops? In my breeds I wouldn't expect them to actually fight with anything before their hormones kicked in at about 8 months + (collies) and over a year for the zois, even then I would be dissapointed if they did.

Back to the original post, puppy play can sound horrific and look awful as they drag each others around by bits of skin, I would always just leave them to it though, thats how they learn :) As Brainless said, Mum will sort them out if she thinks they need it, and plenty of toys, empty plastic bottles, rags to pull etc help :)

I was always told that puppies learn bite inhibition from their siblings, so even though it sounds and looks horrific I usually leave them to it. If it sounds as if it's getting out of hand I do interfere, but I try to distract them rather than separate them. Saying this, I'm sitting typing as my smallest bitch is trying to take chunks out of her biggest brother ;) Off to distract her. Pity it's raining. They don't want to go outside to play today. Can you get wellies and sowesters (sp?) for puppies :D

The breed is [removed]and this is not normal. However both puppies were fine with their siblings (mine still meets with two of his brothers regularly for walking/play) and are fine with other dogs. They have both attended APDT training classes which has involved mixing with other dogs without problems, they both are walked regularly off the lead and meet strange dogs without problems but put the two of them together and within a few minutes they would start eyeballing each other, they just didn't like each other! I have discussed it with other breeders who have never experienced this, I always seem to have the 'One Offs'.

Very fortunate you didn't decide to keep them both