
I'm afraid big dogs are perfectly capable of mating small bitches, but unfortunately the bitch is often injured, and if she does get pregnant the pups are often too big for her and can result in the bitch's death at whelping. So I can't stress enough
do not leave her unattended outdoors at any time.
The main sign of being in season is having a swollen vulva and a bloody discharge, which often eases off and turns paler in colour around the middle part of the season - this is when most bitches are most fertile and willing to mate (sometimes running off to do so). However the fertile time isn't set in stone - bitches have had successful pregnancies from matings as early as 5 days or (like mine) as late as day 20.