My cocker spaniels had 10 puppies on Monday 2 was born dead and another 5 have died since I am now left with 3 and worried that they may also die mum seems OK she is eating well and she is cleaning and feeding the others she has had litters before and not lost any puppies but 12 months ago our dog tied with her and because we thought she needed a break we took her to the vets where she was given 2 injections to prevent the pregnancy(she had just had a litter) could this injection have anything to do with it.

What does your Vet say? It is impossible to know the answer to this without examining the puppies and the mother.

You apparently DO have a Vet who is familiar with the dog - I would call the Vet.

If she is having problems have you considered having her spayed? It would appear she had "just" had a litter 12 months ago.

Unlikely... has the mother and the puppies been to the vet yet?

There could be any one of a hundred things that cause puppies to die shortly after birth, none of which I would like to take a guess at.

I know you don't want to hear it but please get her spayed once the puppies have weaned. 2 litters is more than enough from a backyard breeder.

I would take these dogs to the vet immediately, and I totally agree with what shazzy and judy are saying.
I've also noticed over the years, if a mother feels her young are unhealthy she will also kill them off. My friend had that problem when her first and only litter of dogs was born sick, the mother would refuse them food and lay on them... BUT.. that does not mean the should not be taken to the vet.. I also believe you should spay your female so this does not happen again and so you do not produce many unwanted puppies. Our worlds shelters are too full to begin with, with not enough loving homes for all the animals... I myself, bought my dog from a very reputable breeder, He's a stud dog.. breeders pick.. but I am still undecided as to if I am going to fix him or not.. I also plan on getting a shelter dog (fixed of course) as soon as I am in my own place and I have the room. I may be moving up north so I don't want to get too many animals before that move is made.. please be a responsible pet owner, and get this looked at..

I'm just going to echo every thing every one has said here, take mom and pups to vet and after they are weaned get her spayed. There are millions of un wanted dogs getting euthanized daily in North America, you don't need to be a helping hand to the over population of shelters. I'm sorry thins sounds harsh, but no one here can tell why your puppies are dying. I am sure we all have out opinions on why this is happening, but no one can ever know for sure. Please take them to the vet.

Take them all to the vet and please do not over breed Momma dog.