An automated experimental milker for rat.

The development of sucking pressure was investigated with an artificial nipple in 16 male and female rat pups on postnatal days 4, 7, 10, 14, and 18. The rat pups refused to suck on the artificial nipple on postnatal day 14 or day 18 thus negative sucking pressure had to be calculated by regression analysis. As a result, the mean maximum intra-oral negative sucking pressure on day 18 was calculated to be -160.1 mmHg in the male and -103.4 mmHg in the female. Based on these results, the maximum level of negative pressure of the automated experimental rat milker was set at -160 mmHg. The automated experimental milker for rat is able to collect milk from lactating mothers by alternating negative and atmospheric pressures through two solenoid valves and a vacuum pump attached to a microcomputer. Mother rats were milked with the automated experimental milker on postpartum days 4, 7, 10, 14 and 18 of a single lactation period. The maximum mean milk yield with this machine was 3.18 +/- 1.37 g, obtained on day 14 of the lactation period. This quantity is considerably lower than previously reported values obtained by measuring differences in body weight of the offspring and mother rat before and after suckling. It is necessary to further optimize this system, but the milk yield in the present study is adequate for chemical analysis.