Different portions (stalks, cobs, plant leaves, and cob leaves) from mature dry maize plants remaining after grain harvest were collected on two occasions, 8 weeks apart. Composition (proportion of plant portions) differed considerably between first and second cutting dates. All plant portions were treated with NaOH. Initial IVOMD and extent of improvement in IVOMD with NaOH treatment differed between plant portions. The difference in composition between first and second cut· ting dates only marginally affected IVOMD of maize straw before and after treatment with NaOH. However, it is evident that changes in maize straw composition could have a considerable effect on its response to NaOH treatment.