关键词: 无毛小鼠, 繁育, 胸腺

Abstract: The hairless mouse strain was first found in KM mice. It has been bred to 19 th generation for the time being. The life span of the hairless mice was about 24months under grade2 breeding , To testify whether they represent a new mutation strain, we studied their biological characters macroscopically. We found 2 hairless mice (a male and a female respectively) in the sibling of KM mice initially. They were kept and bred by means of random, complete, brother sister inbreeding. Fertility was once reduced in 7 th 9 th generations, but it gradually returned to normal by the method of random, cousin inbreeding. It has confirmed that hair loss of the mice had no relations with aging, nutrition, mainteiteining condition, parasitization and sexuality. Female mice had ability to suckle their children till ablactation. Immature KM hairless mice (KM HM) had pale white fuzz when ablactated. It began to lose hair at day 30. Little residual fuzz could be found around the eyes and root of the tail at day 30 to 42. Then they kept hairless for the rest of lives. The skin of KM HM was smooth and clear, through spleens, could be seen. Some folds of the skin appeared and became obvious on the head and lateral part of the body with aging. KM HM had thymus at birth, whose size and weight were almost the same as the counterparts faith normal hairs. Under grade 2 circumstances, the growth and reproductive ability of KM HM had no difference with that of hairy KM mice. The offspring produced at one pregnancy was from 3 to 13. The mother KM HM had the ability to suckle inborn and occasionally ate her babies in the firstborn. Solid tumors were observed occasionally in the mature mice, but when transplanted to other mice, they could not grow well and gradually disappear, some even did not grow. They occur in two mature female mice at present. Both are located in the trunk. One is about 5 to 6mm apart from groin, the other about 2 to 3mm apart from right forearm. KM HM had thymus and could keep alive when in conventional condition, which were different from nude mice without thymus. The character of KM HM, that their folds on the skin became evident with time going on, was similar to that of reported Yuyi hairless mice and Rhinoceros mice. But hair loss of rhinoceros mice began at 12d after birth, and a few separated hair still existed until 60d. Occasional sporadic tumors, residual fuzz only present in Certain areas and the lactation ability in these KM HM mice seemed to distinguish them from the Yuyi hairless mice. All of above suggest that further investigations need to be continued.

Key words: Hairless mouse, Breeding, Thymus