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 vari eties and 1 brown mid-rib experimental hybrid was measured over 2 yr i n 7 locations, according to earliness as fresh-cut forage from the mil ky stage of the grain to the glazed stage. This study determined the e ffect of the main factors causing variations in plant composition and digestibility. Under satisfactory growing conditions, the digestibilit y of a given maize hybrid increases significantly with growth stage, w hereas 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 thos e 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 mai ze cell walls is not only independent of their content in the plant bu t also lower than that of other forage crops (-10 points for the same ADL/ADF ratio).