Variation in ruminants' preference for tall fescue hays cut either at sundown or at sunup

Plants vary diurnally in concentrations of nonstructural carbohydrates. If ruminants prefer forages with higher total nonstructural carbohydrates (TNC ), then the preference for hays harvested within the same 24-h period may v ary. An established field of tall fescue (Festuca arundinacea Schreb.) was harvested six times in the vegetative stage. Harvests were paired such that each: cutting at sundown (PM) was followed by a cutting the next morning a t sunup (AM). We harvested in this manner three times, resulting in six hay s. The hays were field-dried, baled, and passed through a hydraulic bale pr ocessor prior to feeding. Experiments were conducted with sheep, goats, and cattle, using six animals in each case. During an adaptation phase, hays w ere offered alone as meals. In the experimental phase, every possible pair of hays (15 pairs) was presented for a meal. Data were analyzed by multidim ensional scaling and by traditional analyses. Multidimensional scaling indi cated that selection was based on a single criterion. Preference for PM hay s was greater than for AM hays (P < .01) in all experiments. Increased pref erence was associated with increased TNC (P < .01)and in vitro true DM disa ppearance (P < .01) and decreased fiber concentration (P < .01; NDF, ADF, c ellulose, and ADL). Mowing hay late in the day was effective in increasing forage preference.