In mammals, pregnancy can be described as the period in which a female carries the offspring in its womb from implantation through gestation to the time of delivery. The gestation period is the period in which the fetus develops, starting from fertilization to birth. The gestation period varies from one species to another, depending on the amount of fetus growth before birth. Smaller species tend to have shorter gestation period compared to the larger ones. The length of gestation can also be determined by the breeding season. For instance, species using breeding season usually give birth at specific times of the year, especially when food is available. But which mammals have the shortest gestation period?
Of all the mammals, Virginia opossum or North American opossum has the shortest gestation period. It carries her pregnancy for approximately 12 days after mating and gives birth to 16-20 babies. Opossum can have approximately 1-3 litters per year. It has an estrous circle of 28 days and always in estrus for 36 hours. At birth, the infants are so small that 20 of them can fit in a teaspoon. At birth, the young ones move from the birth canal to the pouch where they stay for about three months. The eyes begin to open after 55 days.
Mouse (domestic white)
Mice experience gestation period of about 19 to 21 days after conception. The pregnancy progresses rapidly despite undergoing several stages. The female mouse experience estrus every three to five days. Most female mice housed with one male mice are likely to bring their pregnancy to term compared to those housed with several males. The male mice produce a chemical substance known as pheromones that cause miscarriage in most female if the pregnancy is fathered by a different male.
The gestation period of a hamster is 18-21 days. It mating is observed, it is possible to roughly calculate the time for the arrival of the young ones. Most of the females can hide their pregnancy until a few days to delivery. Some of the signs of pregnancy include increased the aggressiveness of the female hamster, either to humans or colony. Some species of hamsters like the Dwarf Russian hamster have the ability to delay implantation of the fetus after mating. Thus, the female can regulate her breeding.
Meadow mouse carries a pregnancy for approximately 20 to 21 days and gives birth to about 17 litters per year. The size of a litter may range from 4-8 depending on the region. The newborns are often pink in color, hairless, and weigh approximately 2.3 grams. Their eyes open after 8-9 days and are weaned by the 12th day. 28 days after birth, the young females are sexually mature and can begin to breed. The female takes about 35 days to commence breeding.
The gestation period of a rat is about 22 days but can vary from 21 to 23 days and rarely get to 26 days. Female come to heat every 4-5 days unless when pregnant and also comes to heat ten days after delivery. Rats reach sexual maturity after 5 weeks but they do not have a breeding season. A pregnant rat may have a change in personality, either becoming too aggressive or disinterested in playing with other rats.