BREEDING OF THE NORTHERN GRASSHOPPER MOUSE (ONYCHOMYS-LEUCOGASTER) ASA LABORATORY-ANIMAL

Laboratory matings were attempted to establish breeding colonies of No rthern grasshopper mice, Onychomys leucogaster (which were captured in New Mexico, U. S. A.), as experimental animals. The results were as f ollows. The rate of pregnancy was 75% with cohabitation for more than 30 days, and 4% with cohabitation from 1 to 7 days. Both cases were of monogamous mating. The mean litter size was 3.5+/-1.2, with a range o f 1 to 6. The rate of weaning was 78.8%. The mean gestation period was 27.4+/-2.0 days, with a range of 25 to 31. The gestation period was a chieved by the method of confirming sperm from smears. Further, it was possible to breed all year round in a rearing room with fixed tempera ture and humidity.