Changes in fibre content and degradability during preservation of grass–clover crops

The objective was to investigate whether the concentration, composition and rumen in sacco degradability of the neutral detergent fibre fraction in forages are affected by preservation method. A mixed crop of timothy, meadow fescue and red clover was preserved as hay, direct-cut or wilted silage at succeeding developmental stages. Pure crops of timothy and perennial ryegrass were preserved as direct-cut silage only. In both grasses and mixed crops, and especially at early phenological stages, restricted silage fermentation after addition of formic acid caused considerable degradation of ash-free neutral detergent fibre (aNDFom). In direct-cut mixed and pure grass silages, the aNDFom content was 50 and 40 g/kg DM lower than in the respective fresh crops. For grasses, the indigestible proportion of aNDFom was higher in silages than in the corresponding herbage. There were few differences in fibre characteristics between restrictedly fermented silages and silages that were extensively fermented due to inoculation with lactic acid bacteria. Irrespective of crop developmental stage, wilting for silage production and drying to hay led to a considerable increase in the aNDFom content, amounting to nearly 90 g/kg DM for the grass–clover crop. The increase was possibly caused by formation of N compounds which were recovered in the degradable fraction of aNDFom and of indegradable products. Ensiling reversed effects of wilting on aNDFom. Results indicate that predictions of feed intake or structural value of forages based on total content and degradability of aNDFom may be biased by changes in the fibre fraction during preservation.