Common characteristics of the Sprague Dawley Rat include:

Anatomy and Physiology

Adult body weight: 250 - 300g (female); 450 - 520g (male)
Life span: 2.5 - 3.5 years
Respiratory rate: 70 - 115 breaths/minute
Heart rate: 250 - 450 beats/minute

• The dental formulae is 2(I 1/1, M 3/3) = 16. The incisors are open-rooted and grow continuously. Rats will bite or "pinch" with their sharp incisors if mishandled.
• The esophagus enters the stomach at the lesser curvature through a fold of tissue of the stomach. Because of this anatomical arrangement, the rat is unable to vomit.
• Like the horse, the rat does not have a gall bladder.
• The left lung consists of one lobe; the right lung consists of four lobes.
• The rat has five pairs of mammary glands. Distribution of mammary tissue is diffuse, extending from the ventral midline over the flanks, thorax, and portions of the neck.
• The urethra of the female rat does not communicate with the vagina or vulva; it exits separately just ventral to the vulva.
• The deep gland of the nictitating membrane (Harderian gland) is a pigmented lacrimal gland located behind the eyeball, encircling the optic nerve. The secretion of this gland is rich in lipid and porphyrin. Although many species possess a Harderian gland, it assumes a special importance in the rat. During periods of stress and/or certain diseases, the tears overflow and stain the face around the eyes and nose. When the tears dry, the pigment has the appearance of dried blood. The pigment fluoresces under ultraviolet light and contains little or no blood.
• The rat responds to decreases in ambient temperature by nonshivering thermogenesis, and to increases in ambient temperature by increasing the vascularization of its long tail, which may serve as a thermoregulatory organ. Nonshivering thermogenesis for the most part occurs in brown fat, the highest concentration of which is found in the subcutaneous tissues between the scapulae.

Nutrition

Rats should be fed a commercial rat or rodent diet and water ad lib. These diets are nutritionally complete and do not require supplementation.

Food intake is approximately 5g/100g BW/day; water intake is approximately 10-12ml/100g BW/day

Reproduction

Breeding onset is between 65-100 days of age in both females and males, although females may have their first estrus at 35 days. Rats are polyestrous and breed year round; ovulation is spontaneous. The duration of the estrous cycle is 4-5 days and estrus itself lasts about 12 hours, occurring in the evening. Vaginal smears are useful for determining the stage of the estrous cycle. Mating is usually nocturnal and may be confirmed by the presence of a copulatory plug in the vagina for 12-24 hours post-copulation, although this is not as reliable as indicator as in the mouse. The presence of sperm on a vaginal smear is a good indicator of mating.

The Whitten effect, the synchronization of the estrous cycles of females exposed to the pheromones of a male occurs in rats, but is not as pronounced as in mice. The Bruce effect does not occur in rats.

The average gestation period is 22 days. A fertile postpartum estrus occurs within 48 hours of parturition, and simultaneous lactation and gestation may prolong gestation 3-5 days due to delayed implantation. The average litter size is 6-12. The young are called pups and weight 5-6 grams at birth, are hairless, and have closed eyelids and ears. Cannibalism is uncommon, but females should not be disturbed during parturition and for at least 2 days postpartum. Pups are weaned at 3 weeks of age; weaning weight is 40-50 grams. If the postpartum estrus is not utilized, the female resumes cycling 2-4 days post-weaning.

*Sprague Dawley is the registered trademark of Harlan Industries Inc.