Dairy cow health, milk production, and quality depend on a favorable dietary ratio of energy to protein. Including legumes in pasture, hay, and silage improves milk production and quality; however, high phytoestrogen levels in some legumes such as red clover can compromise cow health and fertility. Field trials were conducted at multiple locations to identify the best species, planting and harvesting/grazing practices, and forage processing methods to maintain perennial legumes in pastures, optimize milk yield and quality, and protect cow reproductive health.

Pastures seeded at 70% legumes and 30% grasses retained <30% legume by the third year. Red clover (RC) showed the greatest persistence and could be replenished by frost-seeding into standing forages. However, RC had the highest phytoestrogen levels, followed by subterranean clover, then alfalfa. White clover (WC), kura clover (KC), birdsfoot trefoil (BT), and cowpea contained ~70-fold less phytoestrogen than RC. Drought, frequent cutting, caterpillar herbivory, or ensiling (vs haying) increased RC phytoestrogen levels. Replacing part of RC in dairy forage with other legumes to limit phytoestrogen intake did not compromise milk production or quality.

Researchers compared several legumes sown with orchardgrass and managed by harvesting 3X/yr (simulating haying) or 5X/yr (simulating rotational grazing) to stubble heights of 5 or 10 cm. Cutting 3X to 5 cm enhanced legume persistence and maintained the lowest weed seedbank populations, while cutting 5X increased weed seedbanks. Pasture legumes, especially white clover, provide important floral resources for pollinators and natural enemies of plant pests, and less frequent (3X) cutting improved floral provisioning by BFT, RC, and alfalfa. Forage crops also sequester soil organic carbon (SOC) and cutting 5X/yr enhanced this ecosystem service.