Genetic variation in rate and extent of the in situ cell wall degradation of maize stalks at silage harvest time

Genetic variation in in situ degradability traits of the NDF part of maize stalks at silage harvest time has been studied, as Dart of the research for an ingestibility criterion in silage maize breeding, for 2 years with nine (including two brown-midrib-3 hybrids) and six hybrids, respectively. The extent of degraded NDF, expressed as a percentage of NDF in original samples, was significantly different between hybrids in each of the eight periods of incubation within cow rumens. After the modelling of degradation curves, the lag times and the contents in degradable fractions were also proved to be subjected to genetic variations in normal hybrids. The rate of degradation was nearly twice as much between extreme hybrids. None of the kinetic traits was related to the biochemical composition of the stalks, except a relation between the lignification degree and the extent of indegradable fraction. The rate of NDF degradation in stalks was free of lignin and cell wall carbohydrate contents. Further studies are now necessary in order to validate that traits of in situ degradability, such as the ratio p(r) = (P-24 - p(8))/(100 - p(72)), could possibly be related to variations in the ingestibility of maize hybrids (p(i) is the extent of degradation after i hours of incubation). (C) Inra/Elsevier, Paris.