early puppy death

[bogart126]

my boxer just had a litter of 5 puppies. after having three succesful litters over three years, her last litter was uneventful but all puppies began dying after their 2nd day of life/exhibiting seizures where their whole body would stiffen up and then relax. sent one puppy for pathology and found the cause of death to be pneumonia. now this litter is starting to exhibit the same symptoms. i've had the mother on gentocin for 2 weeks prior to welping. needless to say this is her last litter but no- one can give me a reason why this is happening. she is up to date on all shots, worming heartworm preventitive and is brucella negative as is the stud. any ideas???