No matter how experienced one is, the moment of whelping is always stressful for breeders and even more so when they have the impression that it is late in starting and the bitch may be past normal term.

Calculating The Date of Whelping

The actual duration of pregnancy does not show any great variation.

In order to have an accurate idea of the date of whelping, it is essential to know the time of ovulation. Gestation in bitches lasts 63 days on average across all breeds. However, its apparent duration, i.e., the interval between mating and whelping, may vary from 56 to over70 days. Many females will accept the male well before ovulation, so mating is possible relatively early. Due to the long survival rate of sperm in the uterus (sometimes up to a week), a bitch may be mated but not actually fertilized until a week later. This makes the duration of gestation appear quite long, although it obviously does not correspond to the actual duration. At the other end of the scale, bitches mated at the end of their estrus period may whelp earlier than planned. The same is true for bitches expecting a large litter because their uterus is too distended and fetuses do not have enough room.

In summary, realizing that a bitch may be fertilized if mated anytime from five days before ovulation to five days after, there easily may be differences of up to 10 days in the apparent duration of gestation, merely counting the interval between mating and whelping.