2. Growth and Development of Baby Rats Ann Muir Thomas November 3, 2001

3. Rat Breeding Facts Rats sexually mature at 6-10 weeks Female heat cycle every 4-5 nights Gestation: 21-23 days Litter size: 1-20, average about 10-12 Females are excellent mothers

4. Day 1 Birthweight: ~5 grams Weight doubles in 48 hours Ears and eyes are sealed No fur but whiskers Milk in stomach visible Can turn upright within 24 hours

5. Day 7 Weight: 20 grams Markings visible Starting to grow fur Creep forwards and backwards Ears open

6. Day 14 Weight: ~35 grams Eyes open Leave nest for short periods Start nibbling on solid food Curious

7. Day 21 Weight: ~60 grams Eat solid food Nurse frequently Very playful Seek human contact

8. Day 28 Weight: 80+ grams Nursing rarely Can be weaned Very playful “Parasites” on mom!

9. Summary Rapid development serves rats’ evolutionary niche. Rats are easy to breed and raise, unlike many other rodents.

10. Rats Make Great Pets!