In both rodents and rabbits, newborn young range from relatively small and altricial, such as many species of mice, rats, hamsters, and domestic rabbits, to large and precocial (well-developed), such as spiny mice, guinea pigs, porcupines, and hares. The milks of species with altricial young tend to be high in water and low in energy, and their young may be unable to eat solid food for 10 days or more. By contrast, the highly precocial guinea pig begins to eat solid foods within a few days of birth, and can be weaned as early as one week of age. Altricial rodents may initially remain attached to nipples for extended periods, obtaining small amounts of milk at frequent intervals. However, in rabbits the young are nursed infrequently, only once or twice a day, at which time they ingest highly concentrated milk (Table 1).
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