The implications for UK upland sheep systems of reducing nitrogen fertilizer application to perennial ryegrass/white clover swards were studied over 3 years. Sward height (3·5–5·5 cm) was controlled for ewes with lambs until weaning using surplus pasture areas for silage; thereafter, ewes and weaned lambs were grazed on separate areas, and sward height was controlled by adjusting the size of the areas grazed and using surplus pasture areas for silage if necessary. Combinations from three stocking rates [10, 6 and 4 ewes ha−1 on the total area (grazed and ensiled)] and four nitrogen fertilizer levels (150, 100, 50 and 0 kg ha−1) provided six treatments that were replicated three times. Average white clover content was negatively correlated with level of nitrogen fertilizer. The proportion of white clover in the swards increased over the duration of the experiment. Control of sward height and the contribution from white clover resulted in similar levels of lamb liveweight gain on all treatments. All treatments provided adequate winter fodder as silage. It is concluded that the application of nitrogen fertilizer can be reduced or removed from upland sheep pastures without compromising individual animal performance provided that white clover content and sward height are maintained. Resting pastures from grazing by changing ensiled and grazed areas from year to year sustained white clover content over a 3‐year period.

The consequences of controlling sward height at two levels, around 5 cm (HS) and around 3·5 cm (LS), during spring and summer by adjusting weekly the proportion of the areas grazed in response to changes in rate of herbage production and utilizing the surplus pasture areas to conserve winter fodder were studied over three complete years for Greyface ewes with their lambs at 15ha−1 (SR15) and 10ha−1 (SR10). The rules used to control grazed sward height resulted in acceptable sward height control in three of four treatments and, by providing supplementary feed when sward height was below target, gave rise to similar levels of individual animal performance. Total output of lamb weaned was greater for the SR15 than for the SR10 flocks (607 vs 477 kg live weight ha−1; P<0·001). Amounts of winter fodder produced were less for the SR15 than for the SR10 flocks [39 vs 213kg dry matter (DM) per ewe; P < 0·001]. Significantly more supplementary feed (10·0 vs 4·4kg DM per ewe; P < 0·01) and hay (13·7 vs 4·0kg DM per ewe; P7lt;0·05) were offered around mating to SR15 flocks than to SR10 flocks. It is concluded that, provided that sward height can be controlled between 3·5 and 5·0cm during the spring and summer and that supplementation is offered when the grazed sward is below 3·5 cm, flock performance will fall within acceptable and predictable limits.

1990). The effect of different pasture management strategies during the weaning-to-mating period on reproductive performance of Greyface ewes. ABSTRACT The effects on reproductive performance of different strategies of pasture management designed to conserve herbage in situ during the late growing season for use during the pre-mating and mating period were studied in three experiments over 3 years with Greyface ewes. Two experiments with 341 ewes compared set-stocking of pasture at 12 ewes per ha on two initial levels of herbage mass with a conservation strategy which left half of the area ungrazed and grazed the other half of the area at 24 ewes per ha from late August until mid October (2 weeks before the start of mating) after which the total area was grazed at 12 ewes per ha. In a third experiment with 124 ewes, the conservation strategy left a quarter of the area ungrazed and varied stocking rate to a minimum of 12 ewes per ha to maintain two initial levels of herbage mass on the other three-quarters of the area and then compared set-stocking at six ewes per ha on this area with set-stocking at 18 ewes per ha on the previously ungrazed quarter of the area during the pre-mating and mating period.Initial levels of herbage mass were within the range of 2000 to 2100 kg dry matter (DM) per ha (7 cm sward height; high) and 1500 to 1700 kg DM per ha (4 to 5 cm; low). Mean herbage accumulation rates between August and October were estimated to be 25 and 44 kg DM per ha per day in the first two experiments. Initial live weight and body condition score also varied considerably between years and subsequent response was influenced by herbage growth rate. Where mean ewe body condition was within the score 2-75 to 3-00, range over the mating period and herbage mass on set-stocked areas was not higher than 2200 kg DM per ha (8 cm sward height) in the pre-mating period or not lower than 1300 kg DM per ha (3-5 cm) at about 3 weeks after mating, the strategy of management did not influence reproductive performance in terms of the number of lambs born. Within these limits, however, reproductive performance was positively related to herbage mass in late August (low = 1-60, high = 1-94).When herbage mass fell below the 1300 kg DM per ha level before or during mating, reproductive performance was improved by a herbage-conservation strategy which maintained ewe body-condition score within the 2-75 to 3-00 range. When herbage mass and growth rate were high, reproductive performance was also improved by a herbage-conservation strategy which restricted the development of excessive body condition before mating by avoiding the increase in barrenness shown to derive from very high levels of body condition.

Continuously grazed rye grassl clover swards with surface heights of 8 to 10 cm at 5 weeks before a synchronized mating and 7·5 cm at mating were grazed by 151 Greyface ewes stocked at 12 per ha until mating. The effects of two stocking rates (eight and 16 ewes per ha) for 6 weeks over the mating and post-mating period were then studied on live weight, body condition and reproductive peformance. Sward height fell more rapidly post mating when stocked at 16 ewes per ha than at eight ewes per ha, but remained above 3·5 cm until 4 weeks after first mating under both rates. Ewes stocked at 16 per ha became significantly lighter and leaner than ewes stocked at eight per ha. There was no significant effect of post-mating stocking rate on reproductive performance in terms of conception rate and lambing rate to first mating or lambing rate to all matings. Reproductive performance of Greyface ewes is therefore unlikely to be adversely affected by post-mating stocking rate on swards of 7 to 8 cm which do not fall below 3·5 to 4·0 cm until 3 to 4 weeks after mating.

The sustainability of white clover in grass/clover swards of an upland sheep system, which included silage making, was studied over 5 years for four nitrogen fertilizer rates [0 (N 0 ), 50 (N 50 ), 100 (N 100 ) and 150 (N 150 ) kg N ha )1 ]. A common stocking rate of 6 ewes ha )1 was used at all rates of N fertilizer with additional stocking rates at the N 0 fertilizer rate of 4 ewes ha )1 and at the N 150 fertilizer rate of 10 ewes ha )1 . Grazed sward height was controlled, for ewes with their lambs, from spring until weaning in late summer by adjusting the proportions of the total area to be grazed in response to changes in herbage growth; surplus pasture areas were harvested for silage. Thereafter sward height was controlled on separate areas for ewes and weaned lambs. Areas of pasture continuously grazed in one year were used to make silage in the next year. For treatments N 0 and N 150 , white clover stolon densities (s.e.m.) were 7670 (205AE4) and 2296 (99AE8) cm m )2 , growing point densities were 4459 (148AE9) and 1584 (76AE0) m )2 and growing point densities per unit length of stolon were 0AE71 (0AE015) and 0AE67 (0AE026) cm )1 respectively, while grass tiller densities were 13 765 (209AE1) and 18 825 (269AE9) m )2 for treatments N 0 and N 150 respectively. White clover stolon density increased over the first year from 780 (91AE7) cm m )2 and was maintained thereafter until year 5, reaching 8234 (814AE3) and 2787 (570AE8) cm m )2 for treatments N 0 and N 150 respectively. Growing point density of white clover increased on treatment N 0 from 705 (123AE1) m )2 to 2734 (260AE7) m )2 in year 5 and it returned to the initial level on treatment N 150 having peaked in the intermediate years. Stolon density of white clover was maintained when the management involved the annual interchange of continuously grazed and ensiled areas. The non-grazing period during ensiling reduced grass tiller density during the late spring and summer, when white clover has the most competitive advantage in relation to grass. The increase in stolon length of white clover in this period appears to compensate for the loss of stolon during periods when the sward is grazed and over winter when white clover is at a competitive disadvantage in relation to grass. The implications for the management of sheep systems and the sustainability of white clover are discussed.