Date of Award
Fall 2025
Project Type
Dissertation
Program or Major
Agricultural Sciences
Degree Name
Doctor of Philosophy
First Advisor
Richard G. Smith
Second Advisor
David A. Mortensen
Third Advisor
Anna K. Wallingford
Abstract
Forage legumes are an important source of feed in animal agriculture. However, some legumes produce phytoestrogens, a group of secondary compounds that mimic the animal sex hormone estrogen. Livestock that consume phytoestrogen-rich forage legumes may experience reproductive problems and can serve as a source of phytoestrogens entering the human food supply through milk. Phytoestrogens in legumes are thought to be involved in mediating plant responses to environmental stress and act as signaling molecules to establish symbiotic relationships with microbes, yet there is little data on how environmental cues or management factors influence phytoestrogen concentrations in forage legumes. This research aimed to fill that gap for multiple forage legume species through a semi-systematic literature review, a field experiment representing a range of harvest practices, and several controlled environment experiments manipulating different environmental cues known to vary in the field. In the semi-systematic literature review, we found that phytoestrogen concentrations can vary widely (from 0.1 to 37.8 mg/g of DM) among different forage legume species and cultivars. Further, phytoestrogen concentrations in the milk of dairy cows can vary from 50.8 to 1,658.9 μg/L, depending on the legume species and proportion of legumes in the feed ration, with equol making up most of the phytoestrogen compounds detected. Adverse reproductive health effects of phytoestrogens on cows include impaired fertility, decreased corpus luteum function, lower conception rates, and increased silent heat. In greenhouse and field experiments, we found that red clover has much higher baseline phytoestrogen levels than white clover, while concentrations in kura clover and cowpea were very low or nondetectable. Among the harvest management practices we investigated, harvest frequency (three versus five cuts per growing season) had the greatest influence on phytoestrogen levels in both red clover and white clover. In the five-cut treatment, phytoestrogens varied widely between cutting events, while in the three-cut treatment, concentrations remained relatively stable across cuts. Individual phytoestrogen compounds showed similar patterns of variability based on harvest frequency. In a greenhouse study where plants were subjected to moisture stress, drought stress increased total phytoestrogen concentration in red clover by 100%. Waterlogging stress did not increase total phytoestrogen concentrations. Among the plant physiological responses measured in red clover, leaf water potential was the best single predictor of variation in formononetin, biochanin A, and total phytoestrogen levels. Phytoestrogen concentrations in kura clover were low or undetectable, regardless of water stress treatment. Two greenhouse experiments were conducted to examine the influence of insect herbivory on phytoestrogen concentrations in red clover, kura clover, and white clover. In experiment I, herbivory over a seven-day period increased phytoestrogen levels in red clover by 112% but not in kura clover. In experiment II, herbivory over a nine-day period followed by a nine-day recovery period, resulted in total phytoestrogen levels in red clover that were 84% higher compared to the control, while only glycitein concentration was increased when herbivory occurred for a full eighteen days. In a growth chamber study manipulating temperature and CO2 concentration, elevated temperature decreased total phytoestrogen concentration in red clover by 50% compared to the ambient control. While elevated CO2 altered the concentration of daidzein in red clover, it did not influence total phytoestrogen concentration. The phytoestrogen concentration in cowpea was below detection level regardless of temperature or CO2 treatment. Taken together, these results suggest that, among forage legumes commonly grown in the Northeast US, red clover is by far the most phytoestrogenic, and that a variety of biotic and abiotic factors can strongly influence its phytoestrogen concentrations.
Recommended Citation
Mandal, Palash, "ENVIRONMENTAL DRIVERS OF PHYTOESTROGENS IN FORAGE LEGUMES" (2025). Doctoral Dissertations. 2957.
https://scholars.unh.edu/dissertation/2957