ALBERT

Notes: An experiment was conducted lo compare the effects of the grazing by ewes and weaned lambs on aftermath and previously continuously grazed perennial ryegrass-dominant swards, at two sward heights (4 and 8 cm) in (he autumn, on changes in structure and growth of the swards. The experiment had a factorial design, was replicated twice and was conducted from mid-August to early November with measurements being made on three occasions in the autumn. Aftermath swards had lower tiller population densities and lower herbage masses than those that had been previously continuously grazed, the differences being greatest in August. On an area basis net growth rates of herbage on aftermaths were lower than those on previously continuously grazed swards in August and September but not in October. Growth rates of herbage were higher on the taller sward, but the senescence rates were similar at the two sward heights. It was concluded that autumn swards may be managed at taller sward heights than summer swards without increasing senescence of the sward and a consequent reduction in efficiency of utilization. The effects of previous sward management on tissue turnover in the autumn were not long lasting.

Notes: Two 1·0 ha plots of a late-heading diploid perennial ryegrass (var. Contender) and a late-heading tetraploid ryegrass (var. Condesa), and two 1·4 ha plots of the tetraploid with Aberystwyth S184 small-leaved white clover, were direct sown in May 1987. Over the three years 1988–90 they were continuously stocked by Mule ewes with Suffolk-cross twin lambs, from early April to the end of August, at a target sward surface height (SSH) of 4–6 cm on one set of plots (constant swards) and, on the other set, al 4–6 cm rising after June to a target 6–8 cm (rising swards). The heights were achieved by variable stocking. Fertilizer N was applied only to the grass plots at the rate of 150- 180kgN ha-1 annually.SSH was mainly within the target 4–6 cm, after higher initial heights at turnout in 1988and 1990. Mean heights of the constant swards (April- August) averaged 5·53, 4·43 and 5·04cm in the three years. The rising swards (July-August) increased in height over the constant swards by an average of 0·88, 0·48 and 0·55 cm, in successive years.Clover content of the herbage mass dry matter in the grass/clover swards increased over each grazing season to average 13·0, 26·5 and 21·2% in the three years, with a high mean stolon density of 130 in m-2 in August 1990. Ryegrass tiller densities in year 3 were 23% higher in the diploid than in the tetraploid swards, which had 43% more than the 10000 tillers m-2 of the tetraploid ryegrass/clover swards.It is concluded that the combination of a densely stoloniferous small-leaved clover with the open growth habit of a tetraploid ryegrass can achieve swards of high clover content under continuous sheep stocking.

Notes: Methods of predicting the in vivo dry matter digestibility (DMD) of heather were examined in studies on ten samples of heather which had been fed to sheep in standard digestibility trials. DMD was predicted with similar accuracy from estimates of in vitro dry matter digestibility (in vitro DMD) and from the concentration of cell-wall constituents. In vitro DMD was found to be between 10 and 18 percentage units lower than DMD. Freeze drying the samples was the only modification to the technique which both increased in vitro DMD and the accuracy of the prediction of DMD. Other modifications attempted were the use of different liquor sources, changes in first-stage incubation time and dilution rate, and nitrogen supplementation of the inocula.The concentration of nitrogen or undigested dietary nitrogen in the faeces could not be used to predict the digestibility of heather with precision. It was concluded that the DMD of a heather diet could be satisfactorily predicted from the in vitro DMD of samples collected from sheep fistulated at the oesophagus.

Notes: The effect of three different vertical structures of a perennial ryegrass-dominated sward, defined by pseudostem heights (cm) — 1·3 low (L), 2·5 medium (M) and 3·5 high (H) — on the bite depth and selection of plant parts within the grazed horizon of the sward by sheep and guanacos was studied. The bite depth (cm) was similar between sheep and guanacos across the different swards (L, 1·5; M, 3·6; H, 3·8) and was related to pre-grazing sward surface height rather than to pseudostem height. There were differences in diet composition between species that were related to differences in selection for plant parts. Sheep had a higher proportion of green leaf in the diet than did guanacos in L (0·84 vs. 0·71, P 〈 0·05) and M (0·75 vs. 0·59, P 〈 0·05) swards, and possibly selected this plant part in H swards in which the proportion of green leaf in the grazed horizon was low (0·45–0·50). Guanacos had a higher proportion of dead leaf and sheath in the diet than did sheep in L (0·23 vs. 0·09, P 〈 0·05) and M (0·30 vs. 0·18, P 〈 0·05) swards, and possibly selected this plant part on these swards, in which the proportion of green leaf in the grazed horizon was high (0·70–0·95). The proportion of pseudostem in the diet of sheep and guanacos was similar across all swards (0·03) and was generally much lower than that in the grazed horizon (0·01–0·18). Guanacos had a higher proportion of dead stem in the diet than did sheep (0·06 vs. 0·02, P 〈 0·05) across all swards, but the proportion was similar to that in the grazed horizon of each sward.

Notes: The effects on herbage intake and ingestive behaviour by ewes and weaned lambs of grazing aftermath and previously continuously grazed perennial ryegrass-dominant swards at two different sward heights (4 and 8 cm) in the autumn were studied. The experiment had a factorial design, was replicated twice and was conducted from mid-August to early November. There were six ewes and six weaned lambs per treatment plot and measurements were made in three periods. The effects of previous treatment of swards on herbage intake by ewes and weaned lambs were greatest in August, with herbage intakes being significantly lower on the aftermath swards. Differences disappeared by October. The lowest herbage intakes were obtained on the aftermath sward at the lowest sward height, with ewes being more affected under those conditions than lambs. Grazing time and biting rate increased with a reduction in sward height and were higher on aftermath swards. However, these increases did not compensate for reductions in estimated bite size on the aftermath swards. It was concluded that the effects of the sward management treatments in the summer on tissue turnover of the sward and herbage intake in the autumn were considerable in the early part of the autumn but had largely disappeared by the end of the autumn period.

Notes: Performance of continuously stocked Mule ewes nursing Suffolk-cross twin lambs over three grazing seasons, between April and August, was compared on swards of N-fertilized diploid perennial ryegrass (D), tetraploid perennial ryegrass (T) and tetraploid perennial ryegrass with white clover (TC), the latter receiving no fertilizer N. Sward height was maintained by variable stocking rate close to a target of 4–6 cm (constant treatment) from turnout and compared in July and August with a rising sward height treatment (target 6–8 cm).Lambs on TC swards had significantly higher (P 〈0·001) liveweight gains compared with lambs on T swards by 41 gd-1 in April–June and by 68gd-1 in July-August. Live weight and body condition score of ewes in August were significantly higher (P〈0·001) on TC compared with T swards, by 11·3 kg and 0·75 respectively. Rising sward heights in July–August increased live-weight gain of lambs compared with constant sward heights by 102, 39 and 54gd-1 in consecutive years, associated with sward height increases of 0·9, 0·5 and 0·6cm respectively. Rising sward height increased ewe live weight and body condition score by 5·1 kg and 0·3 respectively, compared with results from constant sward heights. Effects of sward height and sward type were additive.T swards had a significantly (P〈0·01) 16% greater overall lamb output than the D swards due mainly to a 10% higher achieved stocking rate. Stocking rates of ewes on TC vs T swards were 40, 13 and 12% lower in April-August in successive years. The higher liveweight gain of lambs on the TC swards resulted in lamb outputs of 76, 105 and 101% of the T swards in successive years, showing that grass/clover swards containing over 20% clover could produce similar lamb output ha-1 to grass swards given 150–180 kg N ha-1.

Notes: The effects of sheep grazing on the development of and production from heather swards and on intake and diet selection by grazing Scottish Blackface wether sheep were studied in an experiment in which sheep numbers were adjusted to remove 0, 40% or 80% by weight of current season's shoots in summer and in autumn for a period of 5 years. All combinations of season and level of grazing were provided. The plots were divided after 2 years and grazing was continued for a further 3 years on one subplot but discontinued on the other.Sward productivity during the 5 years of grazing was unaffected at the 40% level of shoot removal but at the 80% level was reduced by up to 66%.After a season's uninterrupted growth at the end of the experiment heather cover and herbage mass were lower and current season's shoots as a proportion of total mass were higher on those treatments which received the greatest severity of grazing. Weight of current season's shoots was unaffected on treatments which had received the 40% level of shoot removal but was reduced by 40% and 50% on treatments which had received the 80% level in summer and autumn respectively. On the rested subplots sward recovery was such that no treatment effects remained after 3 years except with respect to 80% shoot removal in autumn where herbage mass was reduced compared with other treatments.Intakes of digestible organic matter per sheep were higher at the 80% than the 40% level of grazing in the fifth year of the experiment. This was ascribed to the ingestion of new shoot growth from the twig bases on the 80% level of removal treatments. Intake and digestibility were higher in the summer on those treatments which had received the 80% level of removal in previous autumns. Over the 5 years of the experiment there was a small decline in intake and digestibility values, with the decline being greatest in the summer and at low levels of grazing.Floristic changes differed on the rested and grazed areas. On the rested subplots in the fourth year after grazing stopped, heather height was lower and cover by grasses, sedges and herbs was greater on treatments which previously had received the highest levels of utilization. On bare areas the rate of recovery of heather was rapid where shoots as well as seedlings contributed to recovery growth. On the grazed subplots, with the exception of the low-growing ruderal Rumex acetosella, cover due to grasses, sedges and herbs remained low as species other than heather were selectively grazed.Relationships among stocking rates, grazing behaviour and heather utilization are discussed and guidelines for the recognition of overgrazing are outlined.

Notes: A description is given of equipment designed to be fitted to either sheep or cattle, and to record automatically information on the jaw movements associated with both grazing and ruminating, movements of the head in plucking mouthfuls of herbage, and the time spent in grazing. The equipment has been successfully tested against alternative visual and mechanical methods of measuring grazing behaviour.The use of modified equipment in detailed studies has shown (a) that the maximum acceleration of the head in a longitudinal plane when plucking mouthfuls of herbage was twice as great in sheep as in cattle and in the sheep, but not in the cow, increased as sward height decreased; and (b) that the ratio of jaw movements to head movements was always greater than unity in both sheep and cattle, and was greater on tall than on short swards in two out of three comparisons. The rate of biting was significantly lower on tall than on short swards.