The dog that sired Tuffy and one of his siblings were put down last week, The (Raleigh, N.C.) News and Observer reported Monday.
The dogs were poisoned on Easter by someone who fed them fish covered in anti-freeze.
John and Christina Bannow, who bred the dogs, said they concluded that the dogs would not be able to recover.
"Unfortunately I have bad news. Blaze and Nusia are declining with no hope for recovery. This is a very difficult decision for Tina and me, but a decision that has to be made to prevent any further suffering. We will be putting Blaze and Nusia to sleep later today. Thank you all for your support, prayers, and sympathy," John Bannow posted on the Facebook page he maintains as Tarheel Tamaskan.
Bannow said Pasquotank County sheriff's investigators are trying to determine who poisoned the dogs.
"They're talking to people, interviewing people," Bannow said Saturday. They haven't told him whether they have a suspect, however.
Five of the Bannows' dogs were also poisoned on Easter 2011 in the same way. Someone dug a hole in their yard and filled it with fish covered in anti-freeze.
The Bannows' Web site described their dogs' condition after being poisoned.
"Two-thirds of their kidney function was gone and just a few dialysis treatments would not have been able to save them. They would have had to have been on dialysis for the rest of their life and would have suffered greatly," tamaskan-aid.com stated.