Rat Breeding

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I am going to repeat this again, make sure you are breeding Rats for the right reasons. Are you capable of handling what you produce? Do you either have homes for the pups or can you sell them to pet stores? Make sure you house your Rats humanely, making sure they are in a clean non overcrowding environment. We generally use 4-5 females to 1 male. Strict quarantine or isolation of all newly acquired rodents for at least 4 weeks greatly helps prevent disease among pet mice and rats. This recommendation is especially important for pet rodents because of the severity of certain diseases that they may harbor without showing signs of illness. You must also consider that healthy food and beddings are not cheap. Rats and mice should be provided a good quality lab block as a base diet, we use Lab Diet Products. Pregnant and nursing females should also be provided with a good quality kitten kibble such as Iams as well as lab blocks. It is not cheap to feed that many animals, nor is it cheap to provide healthy beddings for that many animals. For the health of the animals, bedding needs to be changed at least once a week, depending on the size of the cage and the number of animals housed in it. A mother rat with babies will likely need her cage cleaned even more often - every couple of days. Some good bedding materials are Care FRESH, Sani-chips, Gentle Touch, Cell Sorb, Aspen, or rabbit pellets. Think about it, it does cost money.

Breeding Age

  • Breeding age of female (optimum) - 3-10 months
  • Breeding age of male (optimum) - 3-24 months
  • Sexually mature- 5-6 weeks of age

Female Statistics

  • Type of estrus- polyestrous (heat at fairly regular times- year round)
  • Frequency of estrus- Every 4-5 days
  • Length of estrus- Usually 12 hours (most often at night)
  • Return of estrus after delivery- 12-24 hours
  • Female menopause- 18 months (variable)
  • Pelvic fusing in females- No
  • Number of teats on a female- 12
  • number of Uteruses- 2 (“uterine horns”)

Pregnancy and Babies

  • Gestation- 21-23 days
  • Weaning age- 21-28 days
  • Average litter size- 6-12 (variable from 1-22)
  • Average size of newborn- 6-7 grams
  • Fur on babies: 7-10 days
  • Eyes open- 12-15 days
  • Ear canal open 12-14 days
  • Descent of testes 15-50 days

Life expectancy

Domestic rats live about 2 to 3.5 years (Pass and Freeth 1993). In a survey of pet rat life spans in the UK, the average lifespan was 21.6 months, and 95% percent had died by age 3 years (Clark 2004) not Bob Clark  the reptile breeder, LOL. In contrast, wild rats living in the wild tend to live for less than one year: 95% of wild rats die before age 1 year (Davis 1948) not Ralph Davis the reptile breeder, LOL.

Rat's age in months

Rat's age in years

Rat's age in human years

1.5 months (puberty)

0.125 years

12.5 years (puberty)

6 months (social maturity)

0.5 years

18 years (social maturity)

12 months

1 year

30 years

18 months

1.5 years

45 years

24 months

2 years

60 years

30 months

2.5 years

75 years

36 months

3 years

90 years

42 months

3.5 years

105 years

45 months

3.75 years

113 years

48 months

4 years

120 years

Note: This is not an exact science, LOL.


These are some of the guidelines we use at the Living Art Reptile’s facility. I hope you find this information helpful. 


Best of luck,


Living Art Reptiles.


Source Information:

Living Art Reptiles, Gary Brown, Mary Ann Isaksen.



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