Behaviour and browse species selectivity of heifers grazing in a temperate silvopastoral system

In Belgium silvopastoral grazing systems associating trees and pasture are instrumental in enhancing dynamic trade-offs between ruminant farming and habitat improvement. A 130-day study was conducted in Belgium from April to September 2013 to evaluate the effects of browsing a combination of shrubs and trees (i.e. hedge) on the selective behaviour of cattle and to relate these observations to changes in forage nutritive value. Twelve Holstein dairy heifers (Bos taurus; 487 kg) were allocated to either a control ryegrass pasture (i.e. control pasture group; CPG) or a pasture plus unrestricted browsing (i.e. browsing group; BG) of a hedge composed of shrubs and trees. Behaviour and selectivity towards the woody species were recorded for 14 h on a daily basis during three consecutive days over spring, early summer and late summer. Leaves and stems of woody species and faecal samples were collected during each season to analyse their nutritive value and predict the dry matter intake by means of near infrared reflectance spectroscopy. Integrating shrubs and trees along a pasture influenced the heifers' behaviour and BG heifers spent 19.3, 5.9 and 5.4% of their time browsing during spring, and early and late summer, respectively (P < 0.001). This behaviour was correlated to the pre-grazing pasture biomass (r = 0.50; P < 0.001). Compared with the summer seasons, the greater browsing activity in spring was associated with higher plant feeding value. Overall, the most ingested species were Carpinus betulus, Cornus sanguinea, Corylus avellana and Crataegus monogyna. It was concluded that cattle use a significant time budget for browsing on temperate ryegrass pasture but further research is required to investigate potential benefits of silvopastoral systems in Belgium.