THE IMPLICATIONS OF CONTROLLING GRAZED SWARD HEIGHT FOR THE OPERATIONAND PRODUCTIVITY OF UPLAND SHEEP SYSTEMS IN THE UK .2. EFFECTS OF 2 ANNUAL STOCKING RATES IN COMBINATION WITH 2 LEVELS OF FERTILIZER NITROGEN

When grazed sward surface height was controlled within the range 3.75- 5.25 cm during spring and summer, the effects of two annual stocking r ates of twenty (SR20) and twelve (SR12) Cheviot ewes per hectare with their lambs and two rates of nitrogen fertilizer, 100 (N100) and 200 ( N200) kg N ha-1 per year on animal performance and yield of silage fro m areas of pasture surplus to grazing requirements were measured. Deci sion rules for management of sward height resulted in good control of swards and consistent and satisfactory individual animal performance a cross treatments. Total output of lamb was greater for SR20 than for S R12 (699 vs 424 kg live weight ha-1; P < 0.001). Yield of silage was l ess for SR20 than for SR12 [27 vs 184 kg dry matter (DM) per ewe; P < 0-001] and less for N100 than for N200 (65 vs 146 kg DM per ewe; P < 0 .01). Around the mating period, when sward height fell below 3.5 cm, s upplementary feed was offered. More concentrates were offered to the S R20 than to the SR12 ewes (12.3 vs 1.2 kg DM per ewe, P < 0.001) and t o the N100 than to the N200 ewes (8.3 vs 5.2 kg DM per ewe, P < 0.01); trends in the amounts of hay offered during that period were similar.