Selective grazing in pure leaf and leaf/culm mixtures of herbage grasses by sheep

Five grazing trials using Suffolk wethers were carried out at Obihiro, Japan from June to July of 1989 and 1990. New methodology was developed to investigate bite weight and bite selection using hand-constructed swards, which were composed of 128 points of plant units spaced 4 cm apart. Leaves and reproductive culms of orchardgrass ( Dactylis glomerata ) and timothy ( Phleum pratense ) were used in five kinds of artificial swards (three pure leaf mixtures and two leaf/culm mixtures). In the leaf/culm mixture, sheep definitely selected leaf units. The inclusion of reproductive culms decreased the number of prehending bites and the total distance of travel between bites. Mean distance of travel between bites was 8·6–10·6 cm. Mean travelling speed was 7·2 cm/s and was not influenced by the inclusion of culms. Total distance of travel between bites was 3·8–4·1 m/min in pure leaf mixtures and 3·4–3·5 m/min in leaf/culm mixtures. The actual area covered by one prehending bite, estimated from direct measurement, was 21–27 cm 2 in pure leaf mixtures and 15–16 cm 2 in leaf/culm mixtures. Decreased bite area in leaf/culm mixtures resulted in decreased bite weight and intake rate. Experimental errors observed were discussed with respect to the biting behaviour of sheep and flexibility of grass leaves.