What effect does having a litter have on the heat cycle, my dog had puppies 8 weeks ago and was wondering if this changes the time scales at all.

It's never had any effect on my bitches. They have continued to come into season when I would have expected them to if they hadn't whelped. But I guess all bitches can be different!

My one always comes in two months later than I would have normally expected.  Then has a dry season later to try and get back into zinc with the rest of the girls.  It is quite handy really because it means she always has 16 months in between each litter giving her proper time to recover.