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- Wistar Albino
- Developed at the Wistar Institute. Wide head, long ears, tail length always less that the body length.
- Sprague-Dawley Albino
- Developed at Sprague-Dawley farms, Wisconsin. Longer and narrower head than Wistar, longer tail, which may equal or be longer than the body length.
- Long-Evans or Lister Hooded
- Developed by Drs. Long and Evans in 1915 by cross-breeding Wistar albino females with a wild gray male. A smaller variety, white with black (or occasionally brown) hood over head and back of neck, with a line down the back.
Life Cycle
| Age (days) | Weight (g) | Development |
| Birth | 5 | hairless, toothless, closed eyes and ears |
| 4 | 10 | hair begins to appear |
| 10 | . | covered with hair |
| 13 | . | eyes and ears open |
| 21 | 30-50 | weaning |
| 40-50 | 150-200 | sexual maturity |
| 72 | 200 - 400 | young adult |
| 250-300 | 270 - 800 | full grown; males larger than females |
| 1000-1300 | . | end of normal life span |
For more on the biology of laboratory rats see the pages of:
*Please note that all procedures involving laboratory rats follow NIH Guidelines for the humane care and use of laboratory animals.
| Last Updated: 12/26/01 |