Relevant traits, genetic variation and breeding strategies in early silage maize

A silage maize hybrid is now considered different from a grain maize hybrid. This paper gives data on relevant agronomic and feeding value traits suitable in a silage hybrid. It also gives data on breeding strategies and genetic variations available to maize breeders. A silage hybrid should have a good and stable biomass yield, and a grain content between 46 and 50 % according to the quantity and the quality of starch in the diet. Earliness of the plant should be adapted to the cropping area, and should be assessed from whole plant experiments. Cold tolerance should be improved to help cropping in northern areas, as well as resistance to soil fungi during the early growth of roots. A well-developed rooting system is necessary to either contribute to a good lodging resistance, or to contribute to a tolerance to water deficiency and nitrogen uptake. Protein content cannot be improved in the usual way, because of a lack of genetic variation, but improvement could be made through an investigation into the genetic variation of the degradability of proteins in the rumen. Digestibility should be investigated through an enzymatic solubility predicted from a NIRS calibration, performed on whole plant samples, allowing also an estimate of the cell-wall digestibility if NDF, starch and soluble carbohydrates were simultaneously given by NIRS calibrations. When available, a criterion of ingestibility should be used. The criteria of feeding value must be relevant to animal performances. To avoid the risk of a genetic drift towards low feeding values during stalk lodging resistance breeding, both traits must be considered simultaneously. Improved feeding value of a silage maize hybrid would also emerge after further investigations into biochemical traits in cell walls, in lignins monomeric composition and linkages between lignin and structural carbohydrates. Silage maize breeders must also take into account the need for feeding cattle at low costs and in environmentally friendly ways. ((C) Inra/Elsevier).