1. Cotton rats were bred as the laboratory animal for experimental filariasis, and the following results were obtained.
2. The average litter size of 209 deliveries was 5.7±1.9 with the maximum of 12.
3. The breeding rate was 87.5% (98 out of 112 pairs) .
4. The average weight at birth was 5.81±0.59 g in males and 5.94±0.89 g in females.
5. The weaning rate was 40.02% (475 out of 1, 187 new-born cotton rats) .
6. The average body weight of male cotton rats was 100 g 12 weeks after birth, whereas that of female cotton rats reached 100g after 19 weeks.
7. The tail ratio at the age of 10 weeks was 37.7% in males and 39.8% in females.
8. The average longevity was 224.0 days (maximum 507 days) in males and 167.5 days (maximum 507 days) in males and 167.5 day (maximum 367 days) in females.
9. The ratio of male cotton rats to females at birth was 1 : 1 (115 to 115) .

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