Prior Pregnancy Affects Milk Production (IMAGE) Cold Spring Harbor Laboratory Caption The mammary gland in previously pregnant mice (bottom row) produces milk earlier in a second pregnancy than in mice of the same age experiencing pregnancy for the first time (top row). For purposes of the experiment, both groups of mice were given slow-releasing pregnancy hormones, which accurately mimic hormonal activity in real pregnancy. Credit Hannon lab, CSHL Usage Restrictions please give credit License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.