The foster mother used to raise axenic mice should have had her own litter no more than how many days before the donor's pups are put in her cage?

• A. 1
• B. 2
• C. 5
• D. 7

Answer: (B)

Timing matters because a dam’s maternal behavior and milk production are strongest right after birth. When donor pups are introduced, using a foster mother whose own litter is within the last two days ensures she is in peak postpartum state, highly receptive to nursing, and more likely to care for the new pups. This improves acceptance, milk transfer, and overall care, which is especially important for axenic pups that must stay in a clean, controlled environment. If the dam’s own litter is beyond a couple of days old, her responsiveness declines and there’s a greater risk of rejection, neglect, or cannibalism, making successful fostering less reliable. So, the best practice is to use a foster dam that has had her own litter within the last two days.