tThe degradation of starch largely determines the feeding value of maize (Zea mays L.) fordairy cows. Normally, maize kernels are dried and ground before chemical analysis anddetermining degradation characteristics, whereas cows eat and digest fresh material. Dry-ing the moist maize kernels (consisting mainly of starch) at high temperatures can influencetheir physical properties and thus their degradation dynamics in the rumen. We comparedthe in vitro degradability of dried maize kernels with that of fresh kernels after incubationin rumen fluid. Maize kernels were obtained from genotypes diverse in starch structure,composition and type of endosperm. These genotypes were grown in greenhouses at differ-ent temperatures during starch accumulation, and harvested at different maturity stages,in two experiments. Starch content was assessed using the amyloglucosidase method. Fer-mentation in rumen fluid was measured using an in vitro gas production technique. Starchdegradation of the kernels was calculated after 6, 12 and 20 h of incubation in rumen fluid.Oven-drying influenced (P < 0.0001) the in vitro degradation of starch in maize kernelsat the different incubation times, with more starch being degraded in the fresh than inthe oven-dried maize kernels, although the differences were small (11–15%). There was aconsistent interaction (P < 0.009 to 0.0002) between oven-drying and genotype, with thehigh-amylose genotype showing larger effects of oven-drying than the other genotypes.The vitreous genotype showed a lower starch degradation than the non-vitreous type. Atearlier maturity stages, the difference between oven-dried and fresh kernels was largerthan at later maturity stages. The temperature during grain filling affected (P < 0.0001)starch degradation but did not affect the difference between fresh and oven-dried samples.Oven-drying reduced the in vitro rumen starch degradation of maize kernels regardless ofgrowing conditions, genotype and maturity stage, but its effect depends on genotype andmaturity.