In situ degradation kinetics of maize hybrid stalks

An understanding in plant factors influencing digestion kinetics could help develop maize cultivars, thus improving digestibility and consequently the production of ruminants. The stalk fraction of maize hybrids was used to study the cell wall digestion of hybrids varying from the brown midrib-3 (bm3) and their isogeneic normal (N) to normal hybrids. Cell wall constituent contents (NDF, ADF, ADL), soluble carbohydrates (SC), in vitro dry matter digestibility (IVDMD) and ruminal degradation kinetics of the dry matter (DM) and the cell wall (measured as NDF) were determined on stalk samples harvested at silage stage (30–35% DM, whole plant). Six comparative studies of in situ degradability involved 3 comparisons of the bm3 and their N isogeneic hybrids (Ex223, Ex234 and Adonis) and 3 comparisons involving 2 extreme genotypes (DK265 and Stefania): each were compared to the control genotype (Adonis). A comparison of the three sets of N and bm3 hybrids demonstrated that the mutation contained a lower concentration of the cell wall constituents. Hemicellulose rather than cellulose was generally present in lower amounts in the cell walls. Higher SC content and IVDMD were also seen in the bm3 maize. Mean effective degradabilities for both DM (64.4 versus 53.2%) and NDF (36.3 versus 29.5%) were higher (P < 0.01) in the bm3 maize stalks than the N counterpart, respectively. In the maize normal material comparisons, the DK265 genotype presented a lower amount in all the cell wall constituents and was greater in SC content and IVDMD than in the Stefania genotype. The effective DM degradability for DK265 (59.9%) was not as high as the bm3 hybrids, but it showed a greater variation within the genotypes (36.1% for Stefania). A higher in situ DM degradability of bm3 maize compared to their counterpart N or between normal material, could be due to the lower cell wall constituent contents, to a decrease in the undegradable fraction as well as increases in the rapidly degradable or soluble fraction and to less indigestibility of the cell walls (NDF). The amount of lignin does not have a significant effect on the degradation rate constant associated with NDF digestion for most maize comparisons, but is closely related to the extent of degradation.