ABSTRACT
Procedures have been developed for easy collection of milk samples without oxytocin injection. Dams were separated from their pups for 24 h, then were hand-milked with or without aspiration. During the lactation period, the collected milk volume increased up to day 10 of lactation, reached a plateau between days 10 and 18 (range, 2.49 1.49 to 4.27 1.26 g/dam/15 min), then was lower on day 21 (2.12 1.32 g/dam/15 min). We validated our method by administering estradiol (E2) from days 10 to 17 of lactation. Treatment with E2 was associated with a dose-related reduction in the number of dams giving milk at sampling on day 18 of lactation (controls: 14/14; E2 at 0.05 mg/kg/d of body weight/d 10/15; E2 at 0.10 mg/kg/d 5/15) and a severe dose-related reduction in milk volume collected (controls: 3.75 1.40 g/dam/15 min; E2 at 0.05 mg/kg/day: 0.80 1.03 g/dam/15 min; E2 at 0.10 mg/kg/d 0.38 0.68 g/dam/15 min). Our results suggest that days 10 to 18 of lactation appear to be the most suitable period for milk collection in lactating rats in regulatory reproductive toxicologic studies; within this period, we recommend either day 16 or day 18 for milk collection.
