Have any breeders noticed certain problems recurring recently?
Such as - smaller than usual litter in numbers, under-sized puppies, dead/mummified puppies, deformed puppies (ie hole in stomach and chest area)?

Any thoughts on possible causes?

I recently had a lab litter like this (just 4 puppies, 1 healthy) and we have established it is not genetic. I have also established that these problems have been experienced in the UK and USA (havent heard of any in Australia or New Zealand yet).

My vet and I would love to get to the bottom of this and are trying to collect as much info as possible. All replies welcome.