Rats & Mice

Biological data

Rats Mice
Average life-span 2½ – 3½ years 1½ – 2½ years
Adult body weight Male: 267 – 500g
Female: 225 – 325g
Male: 20 – 40g
Female: 22 – 63g
Sexual Maturity 6 – 8 weeks 3 – 4 weeks
Oestrus cycle 4 – 5 days 4 – 5 days
Length of oestrus 14 hours 14 hours
Gestation period 20 – 22 days 19 – 21 days
Birth weight 4 – 7g 1 – 1.5g
Litter size 6 – 16 (average 10) 6 – 12 (average 8)
Eyes open 12 – 14 days 12 – 14 days
Weaning age 3 – 4 weeks 3 – 4 weeks

Housing and Husbandry

As rats and mice like to gnaw, cages made of wire with a solid plastic bottom are best. An aquarium with a wire mesh roof can be used but ventilation problems are common. The animals should have a shelter and nesting material provided. They are highly social and should be kept in single sex groups.The cage floor should be covered (e.g. sawdust). It is important to provide toys/cardboard containers to prevent boredom.


To avoid feeding problems it is best to feed your rat or mouse on a commercial pelleted rodent diet which can be supplemented by a wide variety of fresh food, fruit and vegetables. Excessive supplementation can result in dietary imbalance, obesity or gastric upsets. Food bowls should be heavy enough to prevent them being tipped over. Also provide a permanent source of water. A water bottle is less likely to become contaminated by cage debris.

Common Problems

  • Respiratory disease – One of the most problems of rats and mice. Signs include laboured breathing, rattling sounds, sneezing and discharge from the nose. The commonest cause is a bacterial infection or Sendai virus. Affected animals rarely completely recover. Ammonia can irritate the lungs and nose and good cage hygiene is essential. They can also suffer from allergies and can be affected by second hand smoke.
  • Head Tilt- Can be caused by brain problems and more often by inner ear infections. Antibiotics and steroids are sometimes effective.
  • Eyes – Red tears from eyes and nose are a non-specific response to stress and disease.
  • Kidneys – Kidney failure is more likely in old rats. Signs are excessive thirst.
  • Diarrhoea – Can be caused by Salmonella. Tyzzer’s disease (caused by Clostridium piliforme)or other bacteria.
  • Cancer –Mammary tumours are the most common cancer in rats and mice. These can be removed surgically but often recur.
  • Dental Problems –The front incisor teeth can overgrow if they do not meet properly. This can be inherited or caused by gnawing on cage bowls and loosening tooth roots. Treatment is by regular trimming every 4-5 weeks.


This will prevent unwanted pregnancy. Females can be spayed and males castrated under general anaesthetic. Please call the clinic or book an appointment with our exotics nurse for advice.