Grazing Duration Research Articles

Vegetation dynamics and plant species interactions under grazed and ungrazed conditions in a western European salt marsh

Abstract Experiments in exclosures were conducted on a salt marsh in a macrotidal system in western France. The aim of this study was threefold: (1) to compare vegetation dynamics over a period of 8 years in grazed and ungrazed conditions (2) to investigate the response of annual species to grazing duration during seedling establishment (3) to test the effect of an increase in soil nitrogen availability after cessation of grazing on interactions between Suaeda maritima and Puccinellia maritima . In grazed conditions, during all the survey, vegetation was dominated by a short P. maritima sward with the annual Salicornia europaea in the lower and middle marshes. However, after cessation of grazing in 1994, a homogeneous matrix of the forb Halimione portulacoides , quickly replaced P. maritima in the well drained lower marsh. At the middle marsh level, fine sediment and poor drainage maintained P. maritima while the annual S. maritima which tolerates taller and denser vegetation replaced S. europaea. Elymus pungens cover was limited till 2000 but its rising in 2001 let expect its dominance in the future. While P. maritima abundance remained high, spring abundance of annual species such as S. europaea and S. maritima globally decreased with sheep grazing duration on the salt marsh between February and June. Experiments with monocultures of P. maritima and S. maritima demonstrated that nitrogen was a limiting factor on the salt marsh. In a mixed community, a moderate application of nitrogen (15 g N m –2 year –1 as NH 4 -NO 3 ) promoted growth of P. maritima and limited the biomass of S. maritima , but growth of the latter was enhanced by a high application of nitrogen (30 g N m –2 year –1 ). An increase in the abundance of annuals such as S. maritima on the salt marsh is discussed.

Does availability of resources influence grazing strategies in female Svalbard reindeer?

Foraging strategies and range use in wild female Svalbard reindeer (Rangifer tarandus platyrhynchus) were studied in two areas where the historical grazing pressure differed. We mapped vegetation where the reindeer were seen grazing, and related forage availability to characteristics such as home range size, activity budgets and reproductive status. There were significant differences in quantity of forage available between the two areas and the utilization of vegetation types differed between the sites. However, we found no difference in home range size between the two sites, and individual home range sizes were not related to forage quantity, possibly a result of a skewed and small sample size. Even though significant differences in availability of plant species and groups were found, no variation in home range size was found between reproductive and non-reproductive females on Brøggerhalvøya. Neither did we find any differences between areas or between reproductive groups within or between areas in how female reindeer allocated use of time, or in number of steps taken. However, a significant three way interaction indicated that some variance existed between reproductive groups within or between areas, but we do not conclude that this indicate different grazing strategies. Thus, even though variation in the duration of previous grazing has evidently resulted in rather different foraging conditions in our two areas, we detected no differences in present-day foraging behaviour. Thus, our analyses suggest no relationship or feedback between past grazing and current foraging behaviour in these reindeer.

A simulation model of a dairy forage system to evaluate feeding management strategies with spring rotational grazing

Abstract To counteract a decrease in the availability of grazing for feeding dairy cows in France, a simulation model is proposed in the paper, which combines decision and agronomic submodels to study forage system management strategies compatible with spring grazing use. Nine strategies were tested with the model using a sequence of 16 climatic years. Three of these strategies come from a survey in south‐west France and six others were designed with research scientists or farm advisors. The strategies differ in the duration of maize silage feeding, the area dedicated to maize silage and the area dedicated to grass silage. Results from simulation models show that the consequence of a large and constant maize silage area is a high maize silage overstock if there is an early turnout or a high grass silage overstock if turnout is late. The consequence of a low maize area is a high grazing duration combined in some years with feeding shortages. Strategies that have no feeding shortage and a low level of maize and grass silage overstock have a high grazing duration and have no constant maize or grass silage areas. The solution proposed to avoid climatic risk, and its consequences on feeding, is based on two procedures: use of reserve areas for production and allowing the production programme to be modified to take into account fresh information, especially weather records.

Mute swan grazing on winter crops: estimation of yield loss in oilseed rape and wheat

Yield loss due to grazing by mute swans was measured on two fields each of autumn-sown oilseed rape and winter wheat, located in three regions of the UK. Using a paired plot design, a 33.7% reduction in yield (total dry weight of seed) and a 12.1% reduction in the thousand-seed weight was measured in the rape field subjected to the highest grazing intensity. No significant yield loss was measured in the other three fields. Yield loss was related to: (i) the timing of the onset of grazing, and (ii) the duration of grazing (both estimated from counts of mute swan droppings). Management measures which delay the onset of grazing and/or reduce the duration of grazing are therefore likely to reduce yield loss.

Irrigated Wheat Grazing and Tillage Effects on Subsequent Dryland Grain Sorghum Production

Use of conservation tillage has improved sorghum [Sorghum bicolor (L.) Moench] grain yield 10 to 20% in ungrazed wheat (Triticum aestivum L.)–fallow–sorghum production systems. Our objective in this 2‐yr field study was to develop tillage guidelines for systems where the wheat was grazed. Grazing duration on winter wheat and tillage during the fallow period preceding dryland grain sorghum were treatments on Pullman clay loam (Torrertic Paleustoll). Grazing increased surface soil compaction and reduced wheat residues. Surface soil (0–5 cm) penetration resistance was 0.36, 0.52, 0.75, and 0.92 Mpa, and wheat residue in 1996 was 6.0, 4.8, 3.5, and 1.2 Mg ha for ungrazed and early, normal, and late cattle removal dates, respectively. As a result, sorghum grain yield in 1996, an exceptionally wet season, was 7.9, 7.5, 7.0, and 3.8 Mg ha−1, respectively, with no tillage (NT). In 1997, a dry season with low runoff, only the late cattle removal with NT had reduced yield (3.4 Mg ha−1 compared with 3.9 Mg ha−1 for ungrazed NT). Use of one‐time sweep tillage early in fallow resulted in an increase in sorghum grain yield of 1.9 Mg ha−1 in 1996 for the late cattle removal treatment compared with NT, but it had no effect on yield with the normal cattle removal treatment. In 1997, one‐time sweep tillage increased yield by 0.3 Mg ha−1 with late removal. When wheat residue was ≤2.4 Mg ha−1 following grazing, sweep tillage reduced surface compaction, increased soil water at planting an average of 26 mm over 2 yr, and improved grain yield of sorghum compared with NT. If wheat residues were ≥3.5 Mg ha−1 after grazing, NT was as effective as any tillage treatment. Results agree with conservation tillage guidelines developed on ungrazed wheat.

Effect of timing and duration of grazing of growing cattle in the West African Sahel on diet selection, faecal output, eating time, forage intake and live-weight changes

AbstractSixty-four Azawak male weaned calves were allotted to eight treatments (T) in two trials to study the effect of timing (day or day-and-night) and duration of grazing on diet selection, faecal output, eating time, forage intake and weight changes. Grazing time during the day was 6 h for T 1, 2 and 3; 9 h for T 4, 5 and 6; and 12 h for T 7 and 8. Night grazing time was 0 h for T 1, 4 and 7; 3 h for T 2, 5 and 8; and 6 h for T 3 and 6. The trials were conducted from July 1995 to May 1996 covering the wet (WS), early dry (EDS) and late dry (LDS) seasons. Eight oesophageally fistulated steers were used in a cross-over design to sample the diet selected by day-grazers (D1) and by day-and-night-grazers during the day (D2) and at night (N2). Forage intake was determined from individual data on faecal output from all the calves and means of in vitro organic matter digestibility of extrusa of the fistulated steers. Water intake and eating time were measured in LDS. In WS there were no differences (P> 0·05) in the quality of the diet (extrusa) selected for D1, D2 and N2. In LDS, crude protein content for D1 was lower than for D2 (73 v . 79 (s.e. 2) g/kg dry matter,P< 0·05). In all seasons, faecal output and forage intake increased with total duration of grazing. Total time spent eating increased linearly with increasing total time allowed for grazing. These results suggest that allowing additional grazing time during the night leads to increased forage intake and consequently provides an opportunity for better animal production, especially in the dry season.

PROGRAZE - an extension package in grazing and pasture management

Grazing management decisions by beef cattle and sheep producers in south-eastern Australia have tended to be influenced more by the needs of livestock, often with little consideration given to the possible short- or long-term production impacts that the duration or intensity of grazing may have on pastures. This is partially due to inadequate knowledge of these impacts on some pasture types. Grazing decisions relating principally to livestock tend to be based on a subjective appraisal of liveweight change and pasture assessments often with inadequate understanding of critical pasture characteristics influencing livestock production or the ability to assess these characteristics. PROGRAZE is an extension package developed to assist beef cattle and sheep producers improve the quality of grazing management decision making so they more efficiently and effectively achieve their production and market targets for livestock and livestock products while maintaining or improving the productivity and sustainability of their pastures. To measure knowledge change, PROGRAZE participants were surveyed before they commenced the course and again at its conclusion. To measure on-farm adoption of the skills and knowledge contained within PROGRAZE, participants were again surveyed about 12 months after completing the course. Five focus groups were conducted as a means of obtaining direct feedback from a range of participants on issues not adequately addressed through the surveys. The surveys showed the most significant area in knowledge change by participants was associated with pasture quality and the influence of pasture characteristics on pasture intake and livestock prodution. There was strong evidence of practice change by participants particularly, grazing decisions associated with pasture management. When asked whether participation in PROGRAZE had resulted in increased financial returns from their grazing enterprise, 89% replied it had and 91% indicated participation would lead to more sustainable pastures. The overall response to PROGRAZE was positive with 59% of those producers who replied to the survey indicating it exceeded or completely met their expectations and another 36% stating that it had mostly met expectations. Ninety-nine percent of respondents indicated that they would recommend PROGRAZE to fellow producers.

The use of cumulative gas production technique to characterize changes in the fermentation characteristics of rumen contents following variable periods of starvation and grazing in dairy cows

AbstractThe effect of the duration of grazing (experiment 1) and starvation time and placement in the rumen of inert bulk material before grazing (experiment 2), on the rumen content ferment ability, was investigated by means of measuring cumulative gas production. In experiment 1, a comparison was made of four durations of grazing (1, 1·75, 2·50 and 3·25 h) after overnight starvation. Rumen samples taken from the cows after 1 h of grazing had higher values of total accumulated gas with less (P < 0·05) time required to reach the maximum fermentation rate than cows grazed for 3·25 h. Following grazing, a 7·75·h starvation period was imposed on the four treatments. The extent of fermentation was significantly lower (P < 0·01) after starvation than immediately after grazing (49·7 v. 60·8% of incubated dry matter (DM), respectively). Experiment 2 consisted of a factorial combination of two durations of starvation before grazing (16·5 (LS) and 2·5 (SS) h) with the presence or absence in the rumen of 12·5 kg of a synthetic indigestible material. Before grazing the total accumulated gas production was less (P < 0·05) for the LS than for the SS cows. After the grazing session, the total gas of rumen samples from the LS cows was significantly higher (P < 0·05) than for the SS cows.This was in agreement with the observed higher DM intake during grazing and DM rumen pools after grazing in LS cows. For both starvation periods, the presence of inert rumen bulk led to a higher total gas, a shorter half-time and less DM left unfermented. The measurement of fermentation kinetics by cumulative gas production was suitable to detect changes in rumen content fermentation patterns due to the clearance of material from the rumen (effect of starvation) or DM intake during the grazing sessions.

LIVESTOCK ACTIVITY AND CHIHUAHUAN DESERT ANNUAL-PLANT COMMUNITIES: BOUNDARY ANALYSIS OF DISTURBANCE GRADIENTS

The impact of domestic livestock on soil properties and perennial vegetation is greatest close to water points and generally decreases exponentially with distance from water. We hypothesized that the impact of livestock on annual-plant communities would be similar to that on perennial vegetation. We used multivariate analysis and semivariograms to locate boundaries and to determine the number and width of different annual-plant zones (referred as biotic zones) on long-term livestock disturbance gradients in the northern Chihuahuan Desert, New Mexico. We estimated abundance of annuals in 0.5-m2 quadrats placed at 30-m intervals on 10 livestock disturbance gradients originating at water points. Tansy mustard, Descurainia pinnata, was abundant in severely disturbed areas and also in areas that are known to have high soil nitrogen content. Amaranthus palmeri was abundant in half of the transects in the zones nearest the water points. The relationships of annual-plant abundance and species richness with distance from water points and with perennial-plant cover were not significant (R2 < 0.1). The number of boundaries and sizes of zones varied with distance from water points, with seasons, and with duration of grazing. The first biotic zone (most severely impacted by cattle) ranged from 75 to 795 m radius for winter–spring annuals and from 165 to 1065 m radius for the summer annuals. Variability in the number and size of biotic zones along grazing gradients was spatially correlated with the frequency and intensity of disturbance, with landscape position, and with patchiness of soil features. There were fewer and larger zones of summer annuals than of winter–spring annuals. Boundary analysis of livestock disturbance gradients provided a method with replication for assessing the impact of long-term livestock grazing on annual-plant communities. Livestock create nutrient-rich patches near water points by mixing dung with soil by hoof action. These nutrient-rich patches support species of annuals that are rare or absent in areas where soils are subjected to low-intensity disturbance.

Effects of previous grazing nutrition and management on feedlot performance of cattle

Management strategies designed to improve grazing animal performance can influence feedlot performance and carcass traits both positively and negatively. In spite of the economic relevance of potential interactions between grazing and finishing performance, controlled experiments evaluating integrated production systems are limited in number. Effects of grazing treatments can result from, or be overshadowed by, changes in gut fill, thus making it difficult to assign precise costs to different phases of production. Published reports have considered the effects of stocking rate, duration of grazing, forage characteristics, supplementation, and growth-promoting implants on subsequent finishing performance. Improvements in cattle performance attributed to changes in stocking rate generally have been neutral to positive with respect to effects on finishing performance. Comparisons among forages have led to the suggestion that forage species may contribute to differences in gastrointestinal fill of grazing cattle, thereby influencing gain and efficiency during the subsequent finishing phase. Creep-feeding suckling calves generally has increased preweaning performance but has had relatively little influence on performance during the subsequent finishing phase. Grain supplementation of stocker cattle during the grazing period has improved grazing performance, but effects on subsequent feedlot performance have been inconsistent. Potential carryover effects from protein and mineral supplementation also have been inconclusive. Lack of congruence among studies is puzzling but may be the consequence of highly varied production systems, differences in experimental procedures, and changes in gut fill or mass of internal organs. Based on the studies reviewed, the expression or absence of compensatory growth during the finishing phase appears to be related to the nutritional quality of forages utilized in the grazing period, with higher quality forages tending to yield greater compensatory effects. The bulk of evidence with suckling cattle and stocker implants suggests that effects on subsequent finishing performance are minimal. Attention is drawn to the noticeable lack of research pertaining to integrated production systems. A more thorough understanding of the interactions among grazing nutrition and management, finishing performance, and carcass traits is needed to facilitate greater economic exploitation of these relationships.

Effect of spring grazing management on perennial ryegrass and ryegrass‐white clover pastures

The aim of this study was to investigate the effects of timing and duration of lax spring grazing on rates of leaf growth, botanical composition, and pasture production in perennial ryegrass swards, with and without white clover. In the first field experiment (September 1992‐March 1993), swards of perennial ryegrass with and without white clover were rotationally grazed by sheep every 21 days to residual heights of 70–100 mm (lax) and every 14 days to 30–50 mm (hard). Two periods of lax grazing—short release (SR) from 26 October to 8 December and long release (LR) from 15 September to 8 December—were compared with conventional hard grazing throughout—early control (EC). All treatments were grazed to 30–50 mm every 14 days from 8 December until the end of March. Swards without white clover received 28 kg nitrogen (N)/ha every 2 weeks as urea. Treatments were arranged in a factorial design with three replicates. Overall, herbage accumulation in the SR and LR treatments was increased by 20 and 30%, respectively, compared to the EC treatment (P ≤ 0.001). Leaf growth in ryegrass and white clover was also increased following lax grazing. In the second field experiment (September 1993‐April 1994) plots were subjected to similar grazing managements, though all spring treatments were imposed at a consistent grazing interval of 21 days and N use on non‐clover swards was reduced to 14 kg/ha every 2 weeks. SR and LR treatments increased herbage production during spring by 24 and 28%, respectively, by increasing tiller weight, and during summer and autumn by 16 and 26% by enhancing tiller population density and leaf growth per tiller and/or stolon. Spring management effects were similar for swards with and without white clover. It is concluded that lax spring grazing management of ryegrass‐white clover swards followed by hard grazing at the time of anthesis enhances pasture production, particularly during the summer—autumn period, by increasing both tiller population density and net leaf growth per tiller. Effects were larger following an extended spell of lax grazing. Contribution of tiller population density differences to these responses is discussed in the second paper in this series (Hernandez et al. 1997, this issue).

Effect of spring grazing management on perennial ryegrass and ryegrass‐white clover pastures

The objective of this study was to investigate the effects of timing and duration of lax spring grazing on tiller dynamics in perennial ryegrass swards, with and without white clover. Two periods of lax grazing—short release (SR) from 26 October to 8 December and long release (LR) from 15 September to 8 December—were compared with a conventional hard grazing—early control (EC). These treatments were applied to swards of perennial ryegrass, with and without white clover, and grazed by sheep. Tiller weight, tiller population density, tiller appearance and death, and stolon population were analysed in a factorial design with three (Experiment 1) and four (Experiment 2) replicates. Tiller weight was increased during the reproductive period, particularly in SR and LR treatments. Also, tiller appearance rate increased in all treatments from September to late January, and was particularly high late in December after grazing of the apices of the main group of reproductive tillers. Lax grazing management increased tiller appearance rate by 53% (P ≤ 0.05) in Experiment 1 and 23% (P ≥ 0.05) in Experiment 2, and tiller loss rate by 40% in Experiment 1 (P ≥ 0.05) and 23% in Experiment 2 (P ≤ 0.05). Over 6 weeks following the return to hard grazing, these effects were reflected in increased tiller population densities of 170, 147, and 115% in LR, SR, and EC treatments respectively in Experiment 1 (P ≥ 0.05), and 97, 110.5, and 36.5% in LR, SR, and EC treatments respectively in Experiment 2 (P ≤ 0.05). It is concluded that the increases in herbage production observed in summer‐autumn following imposition of managements which combined lax spring grazing and hard grazing at the time of anthesis, can be attributed to increased tiller densities. The increase was most marked when the period of lax grazing was longer.

Annual Ryegrass Seed Yield Response to Grazing during Early Stem Elongation

AbstractSpring grazing annual ryegrass (Lolium multiflorum Lam.) seed fields with sheep (Ovis aries) is a common practice. The effects of grazing duration in early stages of stem elongation on seed yield and its components are not well known. We studied four durations of spring grazing annual ryegrass with sheep over a 2‐yr period on an Argiaquic Xeric Argialboll soil. Grazing was begun before onset of stem elongation. Treatments were no grazing (G0) and grazing until one‐third (G1), two‐thirds (G2), or all (G3) primary tillers had their apical meristems removed. Leaf area was progressively reduced by grazing duration. The number of fertile tillers increased with grazing duration in the first year, but the effect was not significant in the second year. Grazing did not affect the number of spikelets per spike or florets per spikelet in the first year. In the second year, G2 and G3 reduced spikelets per spike and had no effect on the number of florets per spikelet, whereas G1 did not affect either character. Both G2 and G3 decreased seed weight in the first year, while G1 had no effect; treatments did not affect seed weight in the second year. Grazing treatment did not affect total herbage dry matter at seed maturity, seed yield, or seed quality in either year. We conclude that, in western Oregon, grazing annual ryegrass in late winter and early spring up to the time when the apical meristem of all primary tillers are removed (G3) does not reduce seed yield. Grazing until about one‐third of primary tillers lose their apical meristem (G1) may actually improve seed yield.

Evaluation of Four Intermediate Wheatgrass Populations under Grazing

AbstractThe grazing season in the central and northern Great Plains could be extended by use of adapted cool‐season grass pastures for spring and fall grazing to augment the native warm‐season range. A grazing trial was conducted to evaluate the forage quality of four intermediate wheatgrass [Thinopyrum intermedium (Host) Barkw. &amp; D.R. Dewey] populations for use in forage‐livestock systems. The cultivars Slate and Oahe and two populations selected for improved IVDMD, ‘Manska’ and NE TI 1, were evaluated. Each population was seeded in the fall of 1987 in three replicated 0.4‐ha pastures arranged in a randomized complete block design. Pastures were stocked with three beef yearlings for 28 d in spring 1989 and 42 d in spring 1990 to provide a stocking rate of 7.5 steers ha−1. Duration of grazing was shorter in 1989 because of inadequate soil moisture. Average daily gain (ADG) and gain per hectare were higher (P ≤ 0.10) in 1989 than 1990, despite the lower (P ≤ 0.10) forage availability and lesser number of grazing days in 1989. Steers grazing Manska in 1989 gained 1.59 kg d−1, compared with 1.42, 1.27, and 1.43 for Oahe, Slate, and NE TI 1, respectively. There were no differences (P &gt; 0.10) in ADG or gain per hectare among populations in 1990. The improvement in ADG resulted in 30 to 65 kg more gain per hectare from Manska compared with the other populations in 1989. These results demonstrate the excellent quality of intermediate wheatgrass for grazing livestock and the impact that modest improvements in forage quality can have on animal performance.

Optimal grazing of a multi-paddock system using a discrete time model

Abstract A general model of rotational grazing is constructed where in each of P consecutive time periods a mob of animals grazes one of m paddocks. The optimal grazing sequence is that which maximises their total herbage intake and satisfies the physical constraints of the grazing system. The total herbage intake is compared for four grazing strategies: continuous grazing, strict cyclic rotation, greedy rotation and optimal rotation. A branch-and-bound algorithm is used to find the global optimum strategy. A 100 ha system is simulated carrying 300–400 dairy cows for 60 days in late winter and early spring with a range of subdivisions and grazing durations to ascertain the effectiveness of the different strategies in maximising intake. It is shown that (1) continuous grazing maximises intake when pasture growth is in surplus to animal requirements, (2) that animals' herbage intake under rotational grazing is likely to be poor unless the rate of rotation is carefully synchronised to the pasture growth rate, (3) that grazing management makes little difference to productivity in comparison to stocking rate and average initial pasture, (4) that there is no reason to expect subdivision of land to increase productivity unless reasons such as pasture trampling on wet soil mitigate against long grazing durations. Greedy rotational grazing is found to increase herbage intake on multipaddock systems with an initially inhomogeneous distribution of pasture.

Sheep Grazing Efficiency and Selectivity on Oregon Hill Pasture

Grazing trials were conducted during early and late spring of 1988 and 1989 to evaluate the impact of sheep grazing duration and stocking density on grazing efficiency and forage selectivity in tall fescue (Festuca arundinacea Schreb.)-subclover (Trifolium subterranum L.) hill pastures near Corvallis, Ore. Grazing treatments were 2, 6, and 10 days duration with corresponding stocking densities 380,130, 78, and 1,390, 460, and 280 ewes/ha during early and late spring trials each year, respectively. Grazing efficiency was generally greater (P < 0.05) for the low density/longer duration (10-day) than for higher density/shorter duration (2-day) treatments. Greater grazing efficiency as duration increased largely reflected higher rates of intake rather than lower levels of non-consumptive forage destruction. Stocking density within a constant grazing duration (2 days) had little effect on grazing efficiency. Within the 10 day grazing treatment, grazing efficiency was highest during the last 4 days and lowest during the first 2 days (P < 0.05). Although short duration/high density grazing is considered to be non-selective, sheep were equally or more selective under very short duration/very high density compared to longer duration/lower density treatments in this study. These results suggest that the very short duration with very high stocking density was not an attractive management option since grazing efficiency was low and sheep were more selective.

Effect of redefoliation on the regrowth and water soluble carbohydrate content of Lolium perenne

Plants of Lolium perenne, set up in a minisward in a glasshouse, were redefoliated at 3, 6 or 3 plus 6 days after defoliation at 2 or 5 cm stubble height. Regrowth, water soluble carbohydrate (WSC) content, and tillers per plant and tiller weight were measured. At the extreme, 70% of plants died when they were defoliated at 2 cm stubble height and redefoliated at 3 plus 6 days later. The mean total regrowth at the 3 leaves per tiller stage (and including the DM yield at each redefoliation) of the surviving plants was 4% of plants not defoliated and cut to the same stubble height. Redefoliation had a less marked effect on plants cut at 5 cm stubble height, reducing total regrowth by 55, 78 and 95%, for plants redefoliated at 3, 6 or 3 plus 6 days, respectively. There was a very significant relationship between tillers per plant and stubble WSC (mglplant) (Adj r2 = 0.90; P = 0.001) or stubble DM (g/plant) (Adj r2 = 0.89; P = 0.001) at the 1+ a leaf stage of regrowth on DM yields at the 3 stage of the regrowth cycle. These results confirm the dramatic effect of redefoliation on regrowth of ryegrass plants, and support the recommendation that grazing duration in the field be restricted to less than 3 days to prevent stock regrazing new leaf.

Spring grazing management and tiller dynamics in a ryegrass/white clover pasture

The objective of this trial was to study the effect of variation in the timing and duration of lax spring grazing on tiller dynamics in perennial ryegrass. Tiller population density, tiller appearance, and tiller death were measured in a sward of perennial ryegrass (cv. Grasslands Nui) and white clover (cv. Grasslands Tahora) grazed by sheep every 14 days to 4 cm (hard) and every 21 days to 7 cm (lax) residues. The experiment comprised 2 lax spring grazing treatments [lax grazing October 26December 8 (H-H-L-H) and September 16 December 8 (H-L-L-H)], plus a hard grazed control (H-H-H-H). Ryegrass tiller density was greater in H-L-L-H than H-H-L-H and H-H-H-H from mid summer until the end of the trial in autumn, mainly because of the difference in tillering activity late in December. Tiller appearance rate increased in all the treatments from September to the end of January, and was particularly high late in December in the second regrowth after grazing of the apices of the main group of reproductive tillers. The lax grazing management strategy increased tiller appearance rate during late December and January. Higher tiller losses in lax grazing treatments over the same period were not offset enough to affect this advantage. The response in tiller population density was greater following the extended period of lax spring grazing. Keywords: grazing management,Lolium perenne, reproductive growth, tiller population density, tiller demography, Trifolium repens

Effect of sward height during late pregnancy on intake and performance of continuously stocked June- and August-lambing ewes

Herbage organic matter intake (OMI), grazing behaviour and ewe and lamb production were measured during the last 4 weeks of pregnancy in 2-year-old and mixed-age Border LeicesterxRomney ewes due to lamb in June (winter) or August (spring). The intake of herbage (averaged across lambing date groups) was 1.4�0.1, 1.71�0.1, 1.7�0.1 and 1.9 9�0.1 kg OM ewe-1 day-1 (mean � s.e.m., P &lt; 0.01) for ewes continuously stocked on 10-year-old ryegrass (L. perenne) and white clover (T. repens) pastures maintained at sward surface heights (SSH) of 2.0, 4.0, 6.0 and 8.0 cm respectively. Ewes that were in a good body condition score achieved their required daily intake of energy at a SSH of 2.0 cm. Relative to ewes on the 8.0 cm SSH treatment, those on the 2.0, 4.0 and 6.0 cm SSH treatments attempted to increase intake by increasing grazing duration rather than biting rate. Ewe liveweight, condition score, midside wool growth rate and mean fibre diameter were not affected by sward surface height in either lambing group. There was no within season effect of SSH on lamb birthweight, but lambs born in June were lighter than lambs born in August (4.4k0.2 v. 5.3�0.2 kg, P &lt; 0.001). This trial has shown that, at the same SSH, June-lambing pregnant ewes achieve a similar daily herbage intake to that of August-lambing ewes. A target SSH of 2.0 cm during the last month of pregnancy was shown to be appropriate for both August- and June-lambing ewes in good condition. However, for August-lambing ewes in poor condition, a SSH of 2.0 cm at this stage of pregnancy would be detrimental to overall production, particularly in terms of ewe liveweight loss.

Cost-effectiveness of scaring brent geese Branta b. bernicla from fields of arable crops by a human bird scarer

Brent geese were cost-effectively scared from fields of arable crops (winter wheat and oil-seed rape), in two consecutive winters, by a full-time human bird scarer. The intensity and duration of grazing by geese on winter crops was reduced compared with that of previous years when conventional scaring was used or coloured tapes were suspended over the crops. The geese rarely attempted to visit the wheat fields after one month of intensive disturbance by the human bird scarer, except during a period of exceptionally harsh weather during winter 1990–1991. Brent geese scared from the wheat fields grazed instead on nearby grass pastures. The availability of an alternative feeding area where the geese could graze undisturbed is essential if such effective scaring is to be successful.