Characteristics of suckling stimulation determine the daily duration of mother-young contact and milk output in rabbits

Rabbits nurse inside a nest once/day for 3-5 min. We quantified mother's time inside the nest box (TINB) and milk output as we varied the number and age of pups across lactation. TINB was larger and milk output smaller on lactation days 2, 3, 7, or 8, when one pup (2-3 days old) was provided, but normal on Days 4-6, when suckling eight pups. Maintaining 1, 2, or 6-8 growing pups across 30 days increased TINB in the first two groups without modifying milk intake/pup. Substituting a 15 day-old for a newborn increased TINB (Days 15-20) and decreased milk intake/pup (Days 15-30). Substituting for a newborn on Days 5, 9, 13, 17, 21, 25, and 29 increased TINB on such days and revealed a gradual decline in TINB on the "non-switch" days. Litter size, age, and lactation stage interact to determine TINB and milk output.