Newborn rats, known as pups, are born in an altricial state, meaning they are completely helpless. They lack hair, cannot regulate their body temperature, and have their eyes sealed shut. This extreme vulnerability makes them wholly reliant on the mother (dam) for warmth, protection, and all sustenance during their initial weeks of life until they can feed independently.
Neonatal Nourishment The Role of Milk
For the first two to three weeks, the mother’s milk is the sole source of hydration and nutrition, providing all the energy required for the pups’ rapid growth. Rat milk has a high concentration of both fat and protein, a composition that supports the developmental demands of the neonates. This nutrient density is significantly higher than that found in human milk.
The composition of the milk changes as the pups mature, reflecting their shifting needs. Early in lactation, the fat content is particularly high, sometimes exceeding 12% around day five, but this percentage decreases substantially by the end of the second week. Conversely, the protein concentration remains high, ensuring continuous tissue and muscle development.
Pups locate the mother’s teats primarily through olfactory cues, as their vision is not yet functional. Newborns typically suckle in highly active cycles that occur approximately every three hours.
Maternal Care and Nursing Behavior
The mother’s behavioral adaptations are important for the pups’ survival and successful feeding. The most common nursing position is a specialized posture known as kyphosis, or the arched-back crouch. In this stance, the mother arches her back and extends her legs, creating a protective dome over the litter that maximizes access to her nipples.
One of the most important maternal behaviors is licking the pups, particularly the anogenital region. Since neonates cannot independently urinate or defecate, this tactile stimulation triggers the elimination reflex, which is essential for digestive health. Licking also stimulates circulation and maintains the cleanliness of the nest.
These maternal behaviors are regulated by hormonal drivers. Prolactin plays a major role, helping establish and sustain maternal care and nursing. Oxytocin is also involved, as it triggers the neuroendocrine reflex for milk ejection in response to the pups’ suckling.
The Weaning Process and Solid Food Introduction
The shift from milk dependency to independent feeding is a gradual process that begins before the pups are fully weaned. Around two weeks of age, coinciding with the opening of their eyes, pups become more mobile and curious about their surroundings. At this stage, they begin to sample the solid food and water available to the mother.
Physiological weaning typically begins around day 17, when pups first ingest solid food alongside milk, and it is largely complete by four to five weeks of age. Pups learn about appropriate food sources by mimicking the mother’s feeding habits, tasting the food she has been eating.
The mother plays an active role in this transition by instinctively reducing her nursing time as the pups grow larger. This behavioral shift encourages the young to rely more heavily on solid food and water, promoting their independence. By four weeks old, the pups are fully capable of eating solid food and are no longer dependent on the mother’s milk.