Basic rat statistics
Rats are extremely well studied animals, so we know an enormous amount about their basic biology. Here's a list of the Norway rat's basic biological data (Baker et al. 1979 and Weihle 1987, as reported in Pass and Freeth 1993; additional references noted below). For definitions of some of the terms and measurements used, see the next section.
Life span |
|
|
Captivity |
2-3.5 years |
Pass and Freeth 1993 |
Wild |
<1 year |
Davis 1948 |
Weight |
||
Birth |
5-6 g |
Pass and Freeth 1993 |
Weaning |
30-55 g |
Pass and Freeth 1993 |
Puberty |
150-200 g |
Pass and Freeth 1993 |
At 12 weeks: males |
200-400 g |
Pass and Freeth 1993 |
At 12 weeks: females |
150-270 g |
Pass and Freeth 1993 |
Adult: males |
300-800 g |
Pass and Freeth 1993 |
Adult: females |
250-400 g |
Pass and Freeth 1993 |
Developmental and life history events |
||
Hair coat |
9 days |
Pass and Freeth 1993 |
Incisors erupt |
8-10 days |
Addison and Appleton 1915 |
Eyes open |
12-14 days |
Pass and Freeth 1993 |
Ear canal open |
12-14 days |
Pass and Freeth 1993 |
First leave nest to explore |
14-16 days |
Nelson 1995 |
First molars erupt |
19 days |
Addison and Appleton 1915 |
Second molars erupt |
21 days |
Addison and Appleton 1915 |
Weaning age |
20-21 days (after 2nd molars erupt) |
Pass and Freeth 1993 |
Faint yellow pigment appears on upper incisors |
21 days |
Addison and Appleton 1915 |
Faint yellow pigment appears on lower incisors |
25 days |
Addison and Appleton 1915 |
Descent of testes |
15-50 days |
Pass and Freeth 1993 |
Young rats first appear above ground |
22-30 days |
Adams and Boice 1983, Boice 1977 |
Third molars erupt |
35 days |
Addison and Appleton 1915 |
Puberty: males |
39-47 days |
Engelbrect J. T. et al. 2000, Chappel and Ramaley 1985, Korenbrot et al. 1977 |
Puberty: females |
34-38 days |
Engelbrect J. T. et al. 2000 |
Social maturity |
160-180 days (5-6 months) |
Adams and Boice 1983 |
Menopause (females) |
450-540 days |
Durbin 1966 |
Reproduction |
||
Estrus cycle |
4-6 days |
Pass and Freeth 1993 |
Gestation |
21-22 days |
Pass and Freeth 1993 |
Litter size |
6-14 offspring (varies with maternal age) |
Pass and Freeth 1993, Mohan 1974 |
Maximum milk yield |
12-14 days postpartum |
Pass and Freeth 1993 |
Physiology |
||
Rectal temperature |
38-39º C |
Pass and Freeth 1993 |
Heart rate |
320-480 bpm (beats per min) |
Pass and Freeth 1993 |
Blood pressure: diastolic |
60-90 mm Hg |
Pass and Freeth 1993 |
Blood pressure: systolic |
75-120 mm Hg |
Pass and Freeth 1993 |
Respiratory rate |
85-110 breaths/min |
Pass and Freeth 1993 |
Tidal volume |
1.6 ml |
Pass and Freeth 1993 |
Body surface area in cm2 |
9.1 x g0.66 |
Pass and Freeth 1993 |
Food consumption |
||
Daily food consumption |
5 g/100 g body weight |
Pass and Freeth 1993 |
Daily water consumption |
8-11 ml/100 g body weight |
Pass and Freeth 1993 |
Urine |
||
Urine output per day |
5.5 ml/100g body weight |
Pass and Freeth 1993 |
Urine osmolarity |
1660 mOsm/kg of H20 |
Pass and Freeth 1993 |
Urine pH |
7.5-8.5 |
Pass and Freeth 1993 |
Urine SG |
1.04-1.07 |
Pass and Freeth 1993 |
Blood |
||
Blood volume |
5.6-7.1 ml/100 g body weight |
Pass and Freeth 1993 |
Plasma volume |
3.08-3.67 ml/100 g body weight |
Pass and Freeth 1993 |
Red blood cell count |
7-10 x 106cells/µl |
Pass and Freeth 1993 |
Hemoglobin |
11-19 gm/dl (dl = deciliter) |
Pass and Freeth 1993 |
Packed cell volume |
40.5-54% |
Pass and Freeth 1993 |
Clotting time |
2-5 min |
Pass and Freeth 1993 |
Prothrombin time |
8-4 sec |
Pass and Freeth 1993 |
PTT |
21.1 +- 3.7 sec |
Pass and Freeth 1993 |
Fibrinogen |
190 (150-230) mg/dl |
Pass and Freeth 1993 |
Leukocyte count |
||
Total |
9(6-18) x 103/µl |
Pass and Freeth 1993 |
Neutrophils |
14-20% |
Pass and Freeth 1993 |
Lymphocytes |
69-86% |
Pass and Freeth 1993 |
Monocytes |
1-6% |
Pass and Freeth 1993 |
Eosinophils |
1-4% |
Pass and Freeth 1993 |
Basophils |
Rare |
Pass and Freeth 1993 |
Platelets |
500-1,000 x 103/µl |
Pass and Freeth 1993 |
Definitions
- Basophil: type of white blood cell that releases anticoagulants during an inflammatory response. Involved in allergic reactions.
- Blood pressure, diastolic and systolic: Blood is pumped through arteries by contractions of the heart. When the heart contracts (beats), it sends a surge of blood through the arteries. The highest blood pressure during this surge is the called the systolic pressure. The heart relaxes between beats, and the lowest pressure during this time is called diastolic blood pressure. A blood pressure measurement is made up of both the systolic and diastolic pressure. It is normally recorded as the two pressures separated by a slash, with the systolic number first: systolic/diastolic (e.g. 120/80).
- Body surface area. Body surface area is difficult to measure. It is therefore estimated as: surface area (square cm) = 10 x (mass in g)2/3. The prefactor "10" is empirically adjusted. The prefactor for rats is 9.1. Therefore, to find the surface area of a rat, plug its mass into the equation 9.1 x g0.66. So, a 300 gram rat would have a surface area of 9.1 x 3000.66 = 392.6 cm2
- Eosinophil: white blood cell that contains granules filled with chemicals that damage parasites. Involved in allergic reactions.
- Fibrinogen: protein in blood plasma that is necessary for blood coagulation.
- Hemoglobin: The iron-protein pigment in red blood cells that carries oxygen. measured as the amount of hemoglobin in grams (gm), per deciliter (dl) of whole blood. A deciliter is 100 mililiters.
- Leukocyte: white blood cell.
- Lymphocyte: type of white blood cell of crucial importance to the adaptive immune response. There are two types:B-cells and T-cells.
- Monocyte: large white blood cell that scavenges and destroys invading microorganisms. In the tissues, monocytes develop into macrophages.
- Neutrophil: type of white blood cell involved in defense against bacteria and fungi
- Osmolarity: Total concentration of solutes in a solution. Specifically, the osmotic pressure exerted by a solution across a semi-permeable membrane when compared to pure water. Measured in osmols (Osm). An osmol is an amount of substance that dissociates (breaks apart) in solution to form one mole of osmotically active particles (particles that can pass through the membrane). ref
- Packed cell volume: the ratio of the volume occupied by packed red blood cells to the volume of whole blood.
- pH: logarithmic scale used to describe the acidity or alkalinity of a solution. A pH below 7 is acidic, above 7 is alkaline (or basic), and exactly 7 is neutral.
- Plasma volume: the volume of plasma in the blood. Plasma is the noncellular portion of blood, consisting of water, inorganic salts, and organic molecules.
- Platelet: Smallest of circulating blood cells. Forms plugs on damaged areas and initiates blood clots.
- Prothrombin time: Time necessary for blood to clot. Measures activity of clotting factors I, II, V, VII and X.
- PTT: partial thromboplastin time. Test that measures clotting time in plasma. Focuses on a specific pathway in the blood clotting process.
- Puberty: males: defined here as the time of balano-preputial-separation (BPS). BPS is the androgen-dependent separation of the foreskin (prepuce) from the glans penis (balanus) (Korenbrot et al. 1977, Gaytan et al. 1988). The BPS is not synonymous with puberty, but it is an androgen-dependent event that is necessary for complete copulatory behavior, and is therefore a commonly used index of pubertal development. The BPS just precedes the appearance of mature sperm in the epididymis (Korenbrot et al. 1977). The BPS also precedes the ability to perform full copulatory behavior, because to ejaculate the male must be able to evert the penis from the sheath (Moltz 1975). If male rats are handled by humans every day from day 1 to day 21 (weaning), puberty is delayed by 2.6 days (from age 42.0 to 44.6 days), probably by delaying the LH peak, which in turn delays the androgen peak (Korenbrot et al. 1977).
- Puberty: females: defined here as the time of vaginal opening (VO), also called vaginal patency.
- SG: specific gravity. The ratio of the weight of a volume of liquid to the weight of an equal volume of water.
- Tidal volume: the volume of air inhaled/exhaled during normal breathing. This is not the total volume of the lungs, because the lungs always retain some air during the exhale.