Pasture is the primary source of forage for grazing dairies. In the northern U.S., this requirement is typically met by a May-to-October grazing season, and profitability depends on pastures that provide a uniform, season-long supply of high-quality forage. However, in the northern U.S., seasonal variation in temperature and precipitation creates a challenge, as the predominant forage plants, which include perennial grasses such as Kentucky bluegrass and smooth bromegrass, and legumes such as white clover, undergo a “summer slump” in production.