THE IMPLICATIONS OF CONTROLLING GRAZED SWARD HEIGHT FOR THE OPERATIONAND PRODUCTIVITY OF UPLAND SHEEP SYSTEMS IN THE UK .1. EFFECTS OF 2 ANNUAL STOCKING RATES IN COMBINATION WITH 2 SWARD HEIGHT PROFILES

The consequences of controlling sward height at two levels, around 5 c m (HS) and around 3.5 cm (LS), during spring and summer by adjusting w eekly the proportion of the areas grazed in response to changes in rat e of herbage production and utilizing the surplus pasture areas to con serve winter fodder were studied over three complete years for Greyfac e ewes with their lambs at 15 ha-1 (SR15) and 10 ha-1 (SR10). The rule s used to control grazed sward height resulted in acceptable sward hei ght control in three of four treatments and, by providing supplementar y feed when sward height was below target, gave rise to similar levels of individual animal performance. Total output of lamb weaned was gre ater for the SR 15 than for the SR 10 flocks (607 vs 477 kg live weigh t ha-1; P < 0.001). Amounts of winter fodder produced were less for th e SR 1 5 than for the SR10 flocks [39 vs 213 kg dry matter (DM) per ew e; P < 0.001]. Significantly more supplementary feed (10.0 vs 4.4 kg D M per ewe; P < 0.01) and hay (13.7 vs 4.0 kg DM per ewe; P < 0.05) wer e offered around mating to SR15 flocks than to SR 10 flocks. It is con cluded that, provided that sward height can be controlled between 3.5 and 5.0 cm during the spring and summer and that supplementation is of fered when the grazed sward is below 3.5 cm, flock performance will fa ll within acceptable and predictable limits.