Stem characteristics of two forage maize (Zea mays L.) cultivars varying in whole plant digestibility. I. Relevant morphological parameters

The morphology and rumen fermentation kinetics of the maize cultivars (Zea mays L.) Vitaro and Volens were investigated in detail throughout their growing period as a first step towards understanding the relation between plant characteristics and cell wall fermentability of forage maize. Vitaro is known to have a 9% higher whole plant organic matter digestibility than Volens. Leaf and internode development, fresh (FW) and dry weight (DW) per plant and dry matter content (DMC) of leaves, internodes and developing ears, as well as rumen fermentation characteristics of the stem, were monitored during two seasons. Vitaro plants had a larger final leaf area than Volens plants but their number of leaves (and internodes) was the same. Fully developed Vitaro internodes were shorter and thicker than Volens internodes, resulting in a shorter plant for Vitaro. After anthesis, FW and DW of individual internodes did not vary significantly throughout the growing period. Whole plant FW increased sharply after anthesis, which was associated with the development of the main ear. In both cultivars, DMC of the whole plant more or less doubled between anthesis and harvesting. Vitaro had a higher DW per plant than Volens, but not a larger ear proportion. In rumen fermentation tests on whole stem samples, using the gas production technique, gas production after 72 hours and Tilley & Terry digestibility were significantly higher for Vitaro than for Volens, indicating a higher total degradability for Vitaro. It was concluded that the two cultivars form a suitable model system for studying the causes of differences in rumen fermentation between maize roughages.