Fine-scale discrimination of forage quality by sheep offered a soyabean meal or barley supplement while grazing a nitrogen-fertilized heather (Calluna vulgaris) mosaic

Abstract

The ability of 12 Scottish Blackface ewes to discriminate and concentrate grazing activity in nitrogenfertilized heather patches was determined. The nitrogen content of a stand of heather (Calluna vulgaris) was increased and the fibre content decreased by adding ammonium nitrate fertilizer (7·5 g N/m2) 3 months prior to grazing, in Scotland during August 1991, to selected areas within a patchwork array. The sheep were offered either a high protein (300 g soyabean meal) or low protein (285 g ground barley) supplement daily before being allowed to graze within the heather mosaic during November 1991. The proportion of time spent grazing in fertilized and control patches (patch selection) and the proportion of daylight hours spent grazing (proportion of time spent grazing) was estimated for individual sheep for 6 days. Rumen ammonia concentrations were determined at the end of the grazing period. All animals spent approximately twice as much time grazing in fertilized as in control patches. About half of the daylight hours were spent grazing. The nature of the supplement did not influence patch selection, the proportion of time spent grazing or rumen ammonia concentrations. It was concluded that sheep are able to discern differences in the chemical composition of heather on a fine scale and that their foraging behaviour is not influenced by the type of supplement offered.