A non-spayed female dog’s “heat season” activates between 6 and 36 months of age ... Starting around week two of pregnancy, a female dog will show increased lethargy and weariness.

While the season isn’t constant, female dogs have a 2- to 4-week ... of pregnancy. Carrying puppies to term (the average litter size is 5-6 puppies) puts considerable stress on a female dog ...