Growth of the Mongolian Gerbil, Meriones unguiculatus

Abstract

Patterns of growth and development of the Mongolian gerbil, Meriones unguiculatus, were studied and compared with those of other Cricetid rodents. The gestation period was about 36 days, and litter sizes ranged from 2 to 7. The young averaged 2.57 g at birth, with tail length of 10 mm, hind foot of 9 mm, and ear of 2 mm. Weight increased linearly by a factor of 0.38 g/day. Most growth was completed by the fourth week, though all measurements were still increasing slowly after one year. Eyes opened 18 to 20 days after birth, and weaning was usually completed by the fourth week. The Mongolian gerbil, Meriones unguiculatus, is used widely as a laboratory animal, for the maintenance of certain parasites (Norman and Kagan, 1961; Leland, 1961, 1963; Lewis and Gray, 1961; Boisvenue, 1965), and in studies of water balance (Winkelman and Getz, 1962), endocrinology (Francois, Johnson, and Yong, 1966; Glenn and Gray, 1965; Thiessen, Friend, and Lindzey, 1968), and general physiology (Marston and Chang, 1964; Robinson, 1959). A study has been made of organ weight-body weight ratios (Wilber and Gilchrist, 1965), but the growth rate and patterns of development previously have not been reported. Gestation Period. The gestation period was estimated from a series of six litters born to one pair of gerbils. The least time between successive litters was 36 days. In this instance mating was observed the day the previous litter had been born, and the female refused further advances by the male. The pair was not separated at this time, however, and the gestation period should be verified later. The time intervals between the other litters were 54, 80, 45, and 56 days, respectively. Variations may be due, not only to mating success, but to the age of the previous litter, for it has been reported that gestation periods of other Cricetids are longer for lactating females (Svihla, A., 1935, 1936; Svihla, R.D., 1936). Seasonal Birth Cycle. Mongolian gerbils give birth year around in captivity. This may not be the case in wild populations, however, as evidenced by the September to November birth season for wild Meriones Transactions of the Kansas Academy of Science, Vol. 72, No. 2, 1969. Published September 17, 1969.