Influence of Photoperiod and Thermoperiod on the IVDMD and Cell Wall Components of Tall Fescue1

‘Kenwell’ and ‘Kentucky 31’ tall fescue (Festuca arundinacea Schreb.) were grown in chambers under the following conditions: (a) 27/16 C day/night temperature, 16‐hour photoperiod, (b) 27/16 C day/night temperature, 10‐hour photoperiod, (c) 16/4 C day/night temperature, 16‐hour photoperiod, and (d) 16/4 C day/night temperature, 10‐hour photoperiod. Two harvests were taken. Both long days and high temperatures significantly (P<0.01) lowered the percent in vitro dry matter digestibility (IVDMD) and also lowered the percent in vitro cellulose digestibility of tall fescue. These changes in digestibility were associated with increased levels of structural cell wall components. In the second harvest Kenwell was significantly greater in percent IVDMD (P<0.01) and hemicellulose (P<0.05) than Kentucky 31.