Diet selection by sheep grazing Phalaris aquatica L. pastures of differing water-soluble carbohydrate content

A short-term shading treatment was used to create a Phalaris aquatica L. pasture with alternating strips of ‘low’ [62 mg/g dry matter (DM)] and ‘high’ (126 mg/g DM) water-soluble carbohydrate (WSC) concentration. Analyses showed that starch and all components of the WSC were reduced in concentration by shading. The shaded and unshaded pasture strips did not differ significantly in in vitro DM digestibility (84% DM), nitrogen (3.1% DM), or neutral detergent fibre concentration (42.4% DM). Synthetic alkanes were applied to the pasture strips as markers to measure the selection of the shaded and unshaded pasture by sheep. When 12–13-month-old Merino wethers were given simultaneous access to both pasture treatments, they selected 2.6-fold more unshaded (high WSC) pasture than shaded pasture. The results indicate the involvement of herbage total WSC and its components in the process of diet selection by sheep, and suggest that in future studies, more attention should be paid to reporting data for total WSC concentration.