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 usi ng 58 maize hybrids were carried out in four French environments in 19 95. Near-infrared reflectance spectroscopy (NIRS) was used to determin e in vitro digestibility (whole-plant and cell-wall digestibility) and biochemical composition (starch, soluble carbohydrates, neutral deter gent fibre, acid detergent lignin, protein and ash contents). The 58 h ybrids 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 stud ied and relationships between hybrid mean values for in vitro paramete rs and in vivo digestibilities were examined. For evaluation and breed ing purposes, it is possible to discriminate maize elite hybrids accor ding to their digestibility, especially for discarding low-value genot ypes. 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 satisfact orily relevant to reference data of in vivo digestibility evaluated wi th standard sheep can be obtained to explain about 60% of the variatio n.