Guys my friend who has a female gsd which give birth in january with out him knowing she was pregnant which he want it not to happen again and he sold the puppies in february and he asked me he want to cross the bitch when she comes on heat please when will dog come on heat again.

He just needs to look out for the signs, he needs to be observant not only for heat period, but for health sake, if his dog could get pregnant under his very nose without know

The average is about every six months, though, smaller breeds may go into heat more frequently, as often as 3-4 times a year.