Lactation Studies. VI. Effects of Different Intervals between Nursing and Duration of Suckling on Rate of Milk Production in Sprague-Dawley Rats in the First Lactation

Daily and total amounts of milk produced by 40 Sprague-Dawley rats were measured from the 8th through the 19th day after parturition, using 4-, 6-, 8-, and 12-hr nursing intervals. Ten animals were in each interval and 11 additional rats served as controls. One-half-hour and 1-hr nursing durations were studied with the 4- and 6-hr intervals. Production of milk was measured before and after weighings of litters. Litters remained separated from dams except for nursing. Each litter contained nine young. Milk produced was corrected for losses of feces, urine, and moisture in respiration during nursing. Four dams from each group of ten nursed only their own young and three pairs of dams within each group of ten nursed other litters besides their own to remove litter effect and differences in quantities of milk removed. Dams suckled for 1 hr produced more milk than those suckled for 0.5 hr. The average 12-day milk production of dams suckled by surviving litters for periods of 1 hr with nine young were 418, 318, 278, and 176g for intervals of 4, 6, 8, and 12 hr, respectively. Litter weights at Day 18 disclosed that relative weight difference among groups nursed at different intervals varied greatly from relative differences in milk productions among the same groups. Litter weight gain was a poor indicator of milk production.