There is increasing interest in reducing environmental impacts of grazing ruminants. Recently, the use of high-water-content forages to produce dilute urine, thereby mitigating nitrogen concentrations in excreta and reducing impacts on groundwater, has been encouraged in temperate grazing systems. Of these, some plantain varieties have been suggested to contain diuretic compounds that increase urine production. However, existing research consensus suggests high water content may reduce intake of forages, and, therefore, live weight or milk production. In experiments using long adaptations to forages, the intake of a range of high-water-content temperate forages was measured in pen feeding experiments, along with excreta and identified plant secondary metabolites. High intake was observed across forages, even those of unusually high-water-content, and urine production was strongly positively associated with the resulting water intake, while compounds previously identified as diuretics had no apparent effect. However, there are potentially significant physiological costs in dramatically increased urine losses of carbon and minerals, which may reduce the energy value of diets. Diluted urine of reduced nitrogen concentrations can be achieved with numerous high water content forage species, and with appropriate adaptation, the effect on voluntary intake of high-water-content in the temperate forages studied is limited.

Read the full article in the Journal of Animal Science.