Influence of structure and composition of ryegrass and prairie grass-white clover swards on the grazed horizon and diet harvested by sheep

Diet selection from ryegass‐and prairie grass‐white clover swards, vertically stratified into three horizons (A > 6 cm, B 3–6 cm, C > 3 cm), was studied using oesophageally fistulated sheep during summer and autumn. Animals grazed for 3‐day periods. Apparent herbage intake was calculated from total herbage disappearance. The composition of each horizon and of the diet selected was measured daily. Herbage mass (DM ha‐1) and sward height (cm) prior to grazing were not significantly different between swards in each season, and were 2·0 and 20 in summer and 1·6 and 10 in autumn. In summer, 36% and 5% of the green grass leaf (GGL) for prairie grass and ryegrass, respectively, was distributed in horizons A and B. In autumn 39% and 29% of GGL occurred above 3 cm for prairie grass and ryegrass, respectively. GGL distribution determined which sward horizons were grazed. Sheep grazed horizon C (0–3 cm) of summer ryegrass pasture, and the surface canopy (>3 cm) of all other swards. In summer, apparent intake achieved by sheep grazing prairie grass swards was 87% higher than that achieved on ryegrass swards. In autumn a greater GGL distribution above 3 cm with prairie