Biology of the Hamster

  • Taxonomy
    • Order: Rodentia
    • Suborder: Myomorpha
    • Family: Cricetidae
    • Sub-Family: Cricetinae
    • Genus species:
      • Mesocricetus auratus: Syrian (golden) hamster
      • Cricetulus griseus: Chinese hamster
      • Cricetulus migratorius: Armenian (grey) hamster
      • Cricetus cricetus: European hamster
  • Origin and Habitat
    • The Syrian or golden hamster is native to southeast Europe and Asia Minor (northwest Syria). In 1930, a female and her litter were obtained in Syria and brought to Israel, and, from this family, the domesticated hamster was developed. Syrian hamsters were brought to the United States in 1938.
    • In the wild, hamsters are nocturnal animals that live on brushy slopes and steppes. They generally live alone in deep tunnels (burrows) that insure a cooler temperature and higher humidity than that of a desert environment. Hamsters are omnivorous, making vegetables, seeds, fruits, and meat part of their diet; they store grain in their burrows.
  • Uses
    • Hamsters are the third most commonly used research animal. Ninety percent of these are Syrian hamsters, the other 10% being primarily Chinese, Armenian, and European hamsters. Most Syrian hamsters are a light reddish brown color with a grayish white underside. Other color varieties include cinnamon, cream, albino, and piebald. The longhaired "teddy bear" varieties are popular pets. Several inbred strains are available for biomedical research.
  • Handling
    • Hamsters have a tendency to bite if roughly or improperly handled, startled, injured, or awakened. Two methods to lift a hamster without touching it are to allow the hamster to enter a small container, or to grasp the hamster by the loose skin of the neck area with a rubber-tipped thump forceps. These methods are useful for transferring a hamster from one enclosure to another. A hamster can also be lifted by grasping the loose skin of the neck area with one’s thumb and fingers. A large amount of skin must be grasped firmly so that the hamster cannot turn its head to bite the handler. The hamster can then be inverted and cradled in the palm of the hand. Other techniques to lift/restrain a hamster are to cup the hamster in one’s hands (two-handed technique) and to grip the hamster over the back (one handed technique).
  • Anatomy and Physiology
    • Adult body weight: 95 - 150g (female); 85 - 130g (male)
    • Life span: 1.5 - 2 years
    • Respiratory rate: 35 - 135 breaths/minute
    • Heart rate: 250 - 500 beats/minute
    • Normal average rectal temperature: 102ºF
    • The cheek pouches of the hamster extend to the scapulae and can be everted. When distended, they more than double the width of the animal’s head and shoulders. The cheek pouches are markedly deficient of intact lymphatics, making this area an "immunologically privileged" site. This area is useful for studying tissue or tumor transplantation, as foreign tissue transplanted to the cheek pouch is not subjected to normal rejection.
    • The dental formulae is 2 (I 1/1, M 3/3) = 16. The incisors are open-rooted and grow continuously.
    • Females tend to be larger and more aggressive than males.
    • The stomach is divided into a proximal nonglandular portion and a distal glandular portion. The nonglandular forestomach has some characteristics of a rumen (largest portion of the forestomach of an Ox), such as the nature of the microorganisms present, fermentation, and a higher pH than that of the glandular portion. The two portions of the stomach are grossly distinct.
    • The left lung consists of one lobe, the right lung consists of four lobes.
    • The adrenal glands of the male hamster are larger than those of the female; in other rodents, the reverse is generally true.
    • The urethra of the female does not communicate with the vagina or vulva; it exists separately just ventral to the vulva.
    • The flank or scent glands appear as dark patches on either flank. They are sebaceous glands that function in marking territory and mating behavior. Secretion of the glands causes the hair above them to become wet. The clinical significance of the flank glands is that they are normal structures.
    • Under certain circumstances, hamsters will hibernate, although there is considerable individual and strain variation. Exposure to cold stimulates food gathering behavior, and hibernation requires a temperature of approximately 5 0C. Hibernation is delayed if food is not available for storing. Hamsters do not fatten prior to hibernation, so they must awaken periodically to eat. During hibernation, they are still responsive to external stimuli and usually arouse (usually in a bad mood) if handled or startled to awareness.
  • Nutrition
    • Hamsters should be fed commercial pelleted hamster or rodent diet and water ad lib. These diets are nutritionally complete and do not require supplementation. They eat several small meals approximately 2 hours apart. They are coprophagous and bend the upper half of their body at each defecation to take feces. This behavior occurs approximately 20 times each day. Nursing pups should have access to water bottles, since they require fluids other than milk.
    • Food intake is approximately 10-12g/100g BW/day, water intake is approximately 8-10ml/100g BW/day.
  • Reproduction
    • Breeding onset is at approximately 90 days in both females and males, although females may have their first estrus at 35 days. Hamsters are polyestrous and breed year round; ovulation is spontaneous. The duration of the estrous cycle is 4 days, with estrus and mating usually occurring in the evening. Vaginal smears are not useful for determining the stage of the cycle. As estrus approaches, the vaginal discharge is thin, stringy, and translucent. The end of estrus is marked by the appearance of a copious, tenacious, opaque postovulatory discharge. The female is mated during the evening of the third day following the appearance of this postovulatory discharge. Pregnancy is determined by observing the postovulatory discharge on days 5 and 9 following mating. No discharge indicates pregnancy.
    • The average gestation period is 16 days. Average litter size is 5-9. The young weigh 2-3 grams at birth, are hairless, and have closed eyelids and ears. The postpartum estrus is nonovulatory. Cannibalism is more common with hamsters than other laboratory rodents, and is usually associated with primiparous females during the first week postpartum. Other factors contributing to cannibalism are lack of nesting material and disturbing the females and/or her litter. For this reason, the female and her litter should be left undisturbed for the first week postpartum. The young are weaned at 21 days. Cycling resumes 2-18 days after weaning. This means that the litter intervals can occur every 35 to 40 days.
    • Newborn male hamsters are distinguished from newborn females by noting the general anogential distance and pointed genital papilla in the male. This is best accomplished by lifting the tails of littermates and comparing perineums.
    • Pseudopregnancy of 7-13 days duration occasionally occurs as a result of infertile matings or crowding of females.
  • Diseases of the Hamster
    • Bacterial Diseases
      • Proliferative Ileitis (Wet tail): Escherichia coli
      • Tyzzer’s disease
      • Pasteurella pneumotropica
      • Streptococcus pneumoniae
      • Salmonellosis: Salmonella enteritidis
    • Viral Diseases
      • Lymphocytic Choriomeningitis (public health significance)
      • Sendai virus
      • Pneumonia virus of mice
    • Parasitic Diseases
      • Spironucleleus (Hexamita) and Giardia
      • Trichomonas sp.
      • Syphacia obvelata and Syphacia muris
      • Hymenolepis nana (transmissible to humans)
      • Demodex criceti and Demodex aurati
      • Notoedres sp.
    • Non-infectious diseases
      • Amyloidosis
        • Principal cause of death in hamsters
    • Neoplasia
      • Low tumor incidence