The low energy concentration of forages often limits animal performance. This limitation in performance can be mitigated by either increasing daily dry matter intake (DMI) or digestibility, or both, resulting in greater daily digestible DMI. The diurnal fluctuation in forage composition, especially the increase in water soluble carbohydrates (WSC), provides an economically viable means of manipulating forage composition at harvest. The diurnal effects on forage composition include fluctuation in the concentration of cell-wall, WSC, and possibly crude protein. Tall fescue harvested in the afternoon when compared to morning harvest had greater in vitro true dry matter disappearance (IVTDMD)(855 vs. 840 g/kg) and when fed to steers, greater in DMI (1078 vs. 760 g/meal). This was associated with greater WSC (92 vs. 74 g/kg). Switchgrass harvested in the afternoon when compared with the morning harvest had similar in IVTDMD (622 vs. 620 g/kg) but greater DMI when fed to goats (266 vs. 244 g/meal) and greater WSC (80 vs. 73 g/kg).  In vivo digestion of alfalfa harvest at 0700, 1000, 1300, 1600 and 1900h resulted in increased digestibility starting at 65.9% and peaking by 1600 at 67.0%. Associated DMI of alfalfa increased from 2.83% of body weight (BW) at 0700h and peaked at 3.42% BW at 1900h. Associated with diurnal shifts in forage composition is the degree of selectivity exhibited among animals of the same species as well as among species.  Generally, ruminants select a diet that is greater in digestibility than the diet on offer. The diet selected may also show greater diurnal shifts than noted for the hays when contrasting afternoon and morning harvests. The use of harvest timing within a 24-h cycle is being investigated to maximize the concentration of WSC in the cut forage, drying time on the day of harvest, forage digestibility, and dry matter intake.