Genotypic variation for in vitro criteria and relationships with in vivo digestibility in forage maize hybrids

The aim of this work was to study the genotypic variation for in vitro digestibility and composition traits within maize elite hybrids, and their relationships with in vivo digestibility traits. Experiments using 58 maize hybrids were carried out in four French environments in 1995. Near-infrared reflectance spectroscopy (NIRS) was used to determine in vitro digestibility (whole-plant and cell-wall digestibility) and biochemical composition (starch, soluble carbohydrates, neutral detergent fibre, acid detergent lignin, protein and ash contents). The 58 hybrids were also studied at INRA, Lusignan, France, within a long-term experiment to determine their in vivo digestibility of organic matter and of crude fibre using standard sheep. Genotypic variation was studied and relationships between hybrid mean values for in vitro parameters and in vivo digestibilities were examined. For evaluation and breeding purposes, it is possible to discriminate maize elite hybrids according to their digestibility, especially for discarding low-value genotypes. In vitro parameters, such as in vitro whole-plant digestibility and cell-walt digestibility associated with cell-wall content, can be routinely investigated with NIRS. Accurate criteria that are satisfactorily relevant to reference data of in vivo digestibility evaluated with standard sheep can be obtained to explain about 60% of the variation.