Canine Pregnancy Tips by: PetPlace Staff | | | | | The average canine pregnancy lasts approximately 64 to 66 days. During the first two-thirds of her pregnancy, keep the dog on her normal maintenance diet. The fetus will grow most rapidly during the third trimester; this is when the mother needs a higher-calorie diet (calories and nutrients should be 1 1/2 times greater than the maintenance diet). Do not add supplements or medications unless advised by your veterinarian. Pregnancy diagnosis is usually first reliable around 18 to 19 days of gestation. | |