next heat after whelping first litter of labs

Question
My son's lab had a litter of pups after her first heat, due to his carelessness in keeping her away from the male. These pups are now approximately four weeks old. How soon will she come in heat again? We do not want her to get pregnant again the next heat, but since the female and male are both kept together, I just want to ask if you can give us any idea of when to expect her next estrus. Thank you for any help you can provide.

Answer
Hi Shirley. Please forgive me for taking so long to get back to you. I had a bad computer glitch.

I would watch for her to go into heat in about 6 months. That's the 'normal' length between heat cycles. However, she may go a bit longer in between. I'd start to keep an eye out though in about 6 months from when she went into heat last time.