Easy Procedure for Milk Collection in Lactating Rats

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.