Suboptimal breeding performance, low litter frequency, small litters, or litter loss in C57BL/6J mouse colonies.

To improve colony yield and solve breeding issues: 1) Minimize stress by limiting cage changes to 1-2 times per week and positioning cages away from noisy or high-traffic areas. 2) Keep males with females throughout pregnancy and nursing to avoid stress-induced litter resorption or cannibalism. 3) Capitalize on postpartum estrus by maintaining the breeding pair together consistently. 4) Avoid disturbing cages around parturition (from day -2 of gestation through day +4 post-birth).