C57BL/6J breeder pairs are notorious for pup cannibalism, especially first-time mothers. Pups are often found missing or dead within the first 48 hours of birth, leading to massive losses in cohort generation.

We resolved the C57BL/6J cannibalism issue by introducing three husbandry modifications. First, we placed two extra Nestlets (shredded cotton sheets) in the cage one week before birth, allowing the female to build a deep, enclosed dome nest. Second, we prohibited cage cleaning and all handler disturbances from day -2 of gestation through day +4 post-birth. Third, we supplemented breeder food with high-fat diet pellets and a small handful of sunflower seeds starting three days before parturition to satisfy maternal nesting and foraging behaviors. These interventions increased pup weaning rates from 45% to over 85%.