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 sample s, 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 t o be subjected to genetic variations in normal hybrids. The rate of degrada tion was nearly twice as much between extreme hybrids. None of the kinetic traits was related to the biochemical composition of the stalks, except a r elation between the lignification degree and the extent of indegradable fra ction. The rate of NDF degradation in stalks was free of lignin and cell wa ll carbohydrate contents. Further studies are now necessary in order to val idate 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 inges tibility of maize hybrids (p(i) is the extent of degradation after i hours of incubation). (C) Inra/Elsevier, Paris.