Phytoestrogen content of purified, open- and closed-formula laboratory animal diets

BACKGROUND AND PURPOSE

Phytoestrogens exert estrogenic effects on the central nervous system, induce estrus, and stimulate growth of the genital tract of female animals. Over 300 plants and plant products, including some used in laboratory animal diets, contain phytoestrogens. Therefore, the source and concentration of phytoestrogens in rodent diets were determined.

METHODS

Twelve rodent diets and six major dietary ingredients were assayed for phytoestrogens (daidzein, genistein, formononetin, biochanin A, and coumestrol), using high-performance liquid chromatography. Three rodent diets recently formulated to reduce phytoestrogen content also were assayed.

RESULTS

Formononetin, biochanin A, and coumestrol were not detected. Soybean meal was the major source of daidzein and genistein; their concentrations were directly correlated to the percentage of soybean meal in each diet.

CONCLUSIONS

High, variable concentrations of daidzein and genistein are present in some rodent diets, and dietary phytoestrogens have the potential to alter results of studies of estrogenicity. Careful attention should be given to diet phytoestrogen content, and their concentration should be reported. A standardized, open-formula diet in which estrogenic substances have been reduced to levels that do not alter results of studies that are influenced by exogenous estrogens is recommended.

The use of dirty bedding for detection of murine pathogens in sentinel mice

Sentinel Swiss (CD-1) mice, housed without filter bonnets, were seronegative for mouse hepatitis virus (MHV) for 8 consecutive months in an experimental colony of CD-1 mice. MHV titers had been detected sporadically in sentinel mice housed in this colony during a 2 year period. In an effort to determine whether MHV was still present in the colony, two methods of exposing sentinel mice to an animal room environment were compared under routine husbandry practices. Eight cages (12 mice per cage; 2 cages per rack) of experimental virus antibody free sentinel mice, housed without filter bonnets, were placed on the bottom shelf of 4 of 12 racks in the room. Twice each week, four cages of sentinel mice received a composite sample of dirty bedding (bedding used previously by mice in the room). The remaining four cages of experimental sentinels received fresh non-used bedding. Sentinel mice were bled at monthly intervals for MHV serology. After 4 months, mice from two cages which received dirty bedding seroconverted to MHV and mice from one cage were positive for Myobia musculi (mites). Three weeks later, all four cages of mice which received dirty bedding were positive for MHV and three were positive for mites. In contrast, only two of four cages of mice which received fresh bedding were positive for MHV and all were negative for mites. These findings indicate the importance of exposing sentinel mice to dirty bedding and that MHV and mites may go undetected for several months in a mouse colony when the incidence levels are low where standard sanitation procedures are used.