The Sperm's Long Journey. A man may ejaculate 40 million to150 million sperm, which start swimming upstream toward the fallopian tubes on their mission to fertilize an egg. Fast-swimming sperm can reach the egg in a half an hour, while others may take days. The sperm can live up to 48-72 hours. Only a few hundred will even come close to the egg, because of the many natural barriers that exist in a woman's body.
9.4 Giving birth. Normal delivery. Children that are born between the 36th and 39th week (38 and 41 weeks after the LMP) are considered as being normal deliveries. Statistically, only 2/3 of all children are born within the 3 weeks around the calculated date of birth and around 80 % within a month around the predicted date of birth.
How long it takes for a cow to give birth really depends on her body condition, her experience, how big the calf is inside her, environmental conditions, and whether the calf is presenting normally or not. As a result there really is no set-in-stone time it takes for a cow to give birth. For experienced cows, it's only a matter of 5 to 6 hours until the calf arrives. For a heifer, it can be a few to a number of hours longer. See the related question below for a similar answer. If, by any chance, you are asking how long a cow is pregnant in days, the average is around 285 days long. Please see the related question on the length of gestation below for a more detailed answer. Karin L.