15 juin 1997
auteur
Le maïs ensilage de demain devra permettre de réduire le coût des productions bovines, les intrants et le travail, avec des pratiques culturales préservant l'environnement. L'objectif du sélectionneur est de créer cette variété idéale de maïs ensilage, ou idéotype, qui rassemblerait toutes les caractéristiques agronomiques et alimentaires aux plus hauts niveaux.
Le maïs ensilage de demain sera une variété produisant une biomasse régulière en conditions d'intrants limités, apte à valoriser les effluents animaux, tolérante aux basses températures, avec une résistance élevée à la verse et un ancrage racinaire de qualité. Dans un milieu donné, c'est la valeur du génotype qui conditionne pour l'éleveur la valeur de l'ensilage. Aussi, ces maïs ensilage spécifiques auront-ils été sélectionnés pour leur valeur alimentaire (mesure de la digestibilité de la plante entière et des parois et mesure de la teneur en amidon). La variabilité de l'ingestibilité devra être prise en compte. La valeur énergétique des meilleures variétés devra être de 0,95 UFL/kg de maïs ensilage.
Hybrid maize for silage must now be considered different from maize for grain, and clearly the best grain hybrid is not necessarily the best for silage. A silage ideotype would be a hybrid with a good, stable biomass. The grain content should be about 46%, for the usual amount of concentrate in the diet, but not below this value, possibly above it, nearing 50% in the diet of animals fed more extensively, with only small amounts of concentrate. Earliness of ripening should be adapted to the local conditions, with a good tolerance to low temperatures. A good resistance to lodging is necessary, and also a well-developed root system, which is probably in relation with a better tolerance to water shortage. The feeding value should be assessed taking into account the enzymatic solubility, predicted from a NIRS calibration, and cell wall digestibility, such as that determined by DINAG. Voluntary intake should be considered, when a way of predicting it will be available. The characteristics of feeding value chosen must be relevant to animal performances. To avoid the risk of genetic drift towards low feeding values when breeding for improved resistance to stalk lodging, both characters have to be considered simultaneously. Maize should be grown "ecologically", with a good balance between the requirements of the crop and the nitrogen returned by animal effluents. Locally, the value of the silage depends on the choice of the hybrid. Recommended lists of silage cultivars should therefore contain only hybrids with feeding values not below than 0.90 FU (feed units for lactation), excluding those with values below or equal to 0.88 FU. With elite silage maize hybrids, values of 0.95 FU could be considered, having possibly also larger voluntary intakes. The energy complementation in the diet would then be considered and, depending on the high feeding value of this new roughage, a better economic result could be achieved on the farm. For a stock breeder, the choice of a maize cultivar specially adapted to silage must come first, and he has to bear in mind that the forage it will produce has to be cheap, reliable, and endowed with a high and stable feeding value.
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