Maintenance is a component of all physiological states, defined as no net gain or loss of any nutrients. The nutrients required for maintenance are utilized for daily body functions, such as: metabolism during rest (heart function, breathing, digestion, nervous tissue function), activity for maintenance (walking to food/water, grazing), and temperature regulation.
Horses at maintenance include those kept in pasture and those occasionally used for work for short periods of time. The energy requirement for maintenance is low and can often be met with good-quality forage.
Typically, grain supplementation is not needed. Supplementation with salt or trace minerals may be necessary based on the nutritional value of the forages. Mature grass forages may also lack adequate protein, so a protein supplement may be added to the daily ration.
Craig Wood, University of Kentucky