Review of shrubs and trees in intensive ruminant systems in temperate areas

Using shrubs and trees as forage for ruminants is common in extensive production systems in the tropics, as well as the Mediterranean region and mountain areas. In temperate Europe, the intensification of agriculture led to a decline in the numbers of woody perennials on farmlands. A review of the potential uses of shrubs and trees in temperate intensive systems shows that this concept is rather recent. Few studies have been investigating the potential outputs and limitations of shrubs and trees forage in production systems, while in Belgium and other European countries, agro-environmental policies are promoting the establishment of hedgerows and woody strips that provide shelter to animals against variable climate conditions. Furthermore, it has been found that ruminant species browse the plants, or alternatively, the forage is harvested and fed fresh or preserved as hay, silages or pellets. In both cases, consequences on feed intake control, woody plant survival, dry matter (DM) production and forage quality in terms of crude protein content reduction have been documented. In addition, depending on the plant species and the preservation method, bio-active plant metabolites such as condensed tannins (CT) are also present in the range of less than 1 to more than 100 g/kg foliage DM. Overall, CT may reduce ruminal N degradation, methanogenesis and nematode parasites infestation, while enhancing microbial-protein synthesis, feed use efficiency and systemic animal physiology. Planting shrubs and trees into the agricultural landscape (i.e. silvopastoral system) can further improve biodiversity and environmental services. Nevertheless, agronomic practices, farm management or environmental policy limitations may reduce the use of this fodder resource. Therefore, although silvopastoral systems seem promising in temperate ruminant systems, the current knowledge to their introduction and efficient management need to be cautiously considered.