COMPOSITION AND NUTRITIVE-VALUE OF WHOLE MAIZE PLANTS FED FRESH TO SHEEP .1. FACTORS OF VARIATION

The composition and digestibility by sheep of 15 commercial maize varieties and 1 brown mid-rib experimental hybrid was measured over 2 yr in 7 locations, according to earliness as fresh-cut forage from the milky stage of the grain to the glazed stage. This study determined the effect of the main factors causing variations in plant composition and digestibility. Under satisfactory growing conditions, the digestibility of a given maize hybrid increases significantly with growth stage, whereas it changes very little under poor conditions (low temperatures, drought, etc). For a given dry matter content, genotype effects were significant in only 2 locations and were of similar importance to those of environment (location and year) on a given genotype. As for other forage crops, maize digestibility is closely linked (R = 0.98) to its undigestible cell wall content. In contrast, the digestibility of maize cell walls is not only independent of their content in the plant but also lower than that of other forage crops (-10 points for the same ADL/ADF ratio).