Grazing Frequency Research Articles

‘Grasslands Gala’ grazing brome (Bromus stamineus Desv.)—a new dryland pasture grass

Abstract ‘Grasslands Gala’ is the first cultivar of Bromus stamineus to be developed. It originates from germplasm collected in Chile. Bromus stamineus is a species closely related to prairie grass (Bromus willdenowii) with similar winter growth and summer drought tolerance. It differs by having a greater number of smaller tillers and an excellent tolerance to close and continuous grazing. Like prairie grass, Gala grazing brome exhibits poor tolerance to wetter soils and its use may be restricted to lighter-textured soils in dry regions. The seed of Gala has a longer awn than prairie grass which requires processing to enable seed to be sown with standard equipment. Establishment is rapid and successful when sown into warm soils from late spring until late summer at depths no greater than 25-30 mm. Gala grazing brome is resistent to head smut disease. A role is apparent for Gala grazing brome in pasture mixtures on drought-prone, lighter-textured soils in the dry east coast regions of New Zealand, particularly for pastures subject to close and frequent grazing. Further research is required on this new species.

Diurnal movements, family groups and alertness of vicuña ( Vicugna vicugna) during the late dry season in the Laguna Blanca Reserve (Catamarca, Argentina)

A study of daily movements and aspects of social behavior of vicuñas ( Vicugna vicugna) in Laguna Blanca Reserve (Catamarca, Argentina) was carried out during the last month of the dry season (November). Mean composition of a vicuña family group was one male, 3.6 females and 1.9 offspring. There was a significant interaction between behavior and zone (defined by distance from river). Early in the morning the vicuñas grazed in a location close to their apparent night-time resting area, near the slopes, distant from the river. As the morning went by, walking behaviour increased towards the river and grazing decreased. Activities according to group size were also tested and a positive correlation was observed between frequency of alert behavior per adult and the number of offspring in the family group. Frequency of grazing and walking were related to time of day and zone and not to number of animals in the group, and alert behavior was related to number of offspring.

CORRELATIONS OF DAILY ACTIVITY WITH AVIAN CHOLERA MORTALITY AMONG WILDFOWL

We tested the hypothesis that wildfowl activities can influence the risk of avian cholera (Pasteurella multocida infection) for susceptible birds at Centerville, Humboldt County, California (USA). Avian cholera mortality characteristics from past epizootics were correlated with variations in flock size, habitat use and 11 feeding and nonfeeding behaviors among six empirically defined groups of wildfowl: American coots (Fulica americana), tundra swans (Cygnus columbianus), American wigeon (Anas americana), northern pintails (A. acuta), northern shovelers (A. clypeata)/mallards (A. platyrhynchos), and teal (A. discors, A. crecca, A. cyanoptera). The position of these wildfowl groups in past mortality sequences was directly correlated with mean flock size, time spent on land, and time spent grazing on land or in shallow water. We propose that variations in bird density, habitat use and frequency of grazing may serve as predisposing factors to avian cholera among wildfowl.

Effect of early spring grazing frequency on the reproductive growth and development of a perennial ryegrass tiller population

Abstract A population (1188) of vegetative perennial ryegrass tillers was identified at random in nine paddocks of an existing farmlet experiment. Groups of three paddocks (396 of identified tillers) were grazed every 8, 16, and 32 days from mid August until early November 1984, after which all paddocks were grazed every 32 days until the end of the experiment in May 1985. The physiological status (vegetative or reproductive) of live marked tillers and their orientation in the sward were determined at 7–12-day intervals during the experiment. Paddock botanical composition and tiller density were recorded in October, December, February, and May. Fifty percent of marked tillers became reproductive during the experiment. Reproductive development was concentrated in late October/early November. Different spring grazing frequencies did not affect reproductive development but frequent grazing resulted in tillers that were more prostrate than when grazing was less frequent. Reproductive tillers had a higher over...

Cutting frequency and cutting height effects on forage quality of rough fescue and Parry oat grass

An experiment was conducted to determine the qualitative response of rough fescue (Festuca scabrella var. campestris) and Parry oat grass (Danthonia parryi) to five cutting frequencies and three cutting heights Beginning in mid-May, the same plants were cut every 1, 2, 4, 8, or 16 wk. during a 16-wk period, at heights of either 5, 10, or 15 cm above ground level. The treatments were repeated in 3 consecutive years on the same plants. Crude protein (CP), lignin, and calcium (Ca) were significantly greater for Parry oat grass than for rough fescue, which had greater acid detergent fiber (ADF) and phosphorus (P) concentrations. Increasing cutting frequency in the first year reduced acid detergent-insoluble nitrogen (ADIN), ADF, and lignin but increased CP and in vitro digestibility of dry matter (IVD) in both forages. Repeated treatment over 3 yr tended lo increase ADF and Ca but reduce CP, P, and IVD. In the first year of treatment, CP yields in rough fescue and Parry oat grass were greatest with 2 or 4 cuts during the growing season. However, in the second year of treatment, CP yield was greatest with one or two cuts in rough fescue and with four cuts in Parry oat grass. The data confirm the benefits of repeated grazing within a year to maintain high quality forage but demonstrate the need to limit the frequency of repeated grazing to avoid deterioration and maximize nutrient yield. Nutrient yields and, presumably, benefits to livestock would be greater at a lower grazing frequency on rough fescue than on Parry oat grass. Key words: Festuca scabrella var. campestris, Danthonia parryi, crude protein, acid detergent fiber, in vitro digestibility, forage quality

The effect of stocking rate on the grazing behaviour of Corriedale sheep

The seasonal variation in the diurnal pattern of grazing, the number of grazing periods each day and the mean intake for each period were assessed at four stocking rates (10, 25, 20 and 25 sheep ha −1) of Corriedale wether sheep ( Ovis aries) grazing a mixed pasture with main species of perennial ryegrass ( Lolium perenne L.) and subterranean clover ( Trifolium subterraneum L.). Most grazing occurred during daylight with a peak of activity in the morning and mid-afternoon. Sheep at the higher stocking rates grazed more intensely throughout the day than did those at lower stocking rates ( P<0.05). There was little difference between the grazing intensities of different stocking rates in the afternoon. Limited grazing occurred about midnight, with more sheep grazing at low than at high stocking rates ( P<0.05). In late summer and autumn, sheep at low stocking rates started grazing earlier (15–30 min) in the morning than did those at high stocking rates but this order was reversed in the spring ( P<0.05). From February to May, the pasture conditions at the low stocking rates allowed faster rates of intake so sheep grazed more frequently with more grazing periods and smaller intakes in each grazing period than did those at high stocking rates. In winter (June and July) longer and less frequent grazing periods were observed at all stocking rates. In spring there was little difference between the stocking rates in the number of grazing periods.

Comparative performance of three early-flowering red clovers under sheep grazing in Southland

Abstract Three early-flowering red clovers (Trifolium pratense L.) were evaluated under nyo grazing frequencies either as monocultures or WIth Bromus willdenowii Kunth ‘Grasslands Matua’ prairie grass or Lolium perenne L. ‘Grasslands Nui’ perennial ryegrass for herbage prorductivity and persistence. In monoculture, the diploidexpenmental hybrid G21 (released as ‘Grasslands Colenso’) and tetraploid G22 gave better cool-season growth than ‘Grasslands Hamua’. G22 gave superior spring and summer growth and persisted longer than the diploids. G21 showed more susceptibility to alfalfa mosaic virus than either Hamua or G22. With a companion grass, clover growth and persistency were higher with Nui ryegrass. G22 was inferior to G21 and Hamua when associated with either grass but was more affected by Matua prairie grass. Red clover yields were greater under infrequent grazing.

Performance of six timothy (Phleum pratenseL.) lines in pure swards under grazing

Abstract The long-term persistence of timothy grass (Phleum pratense L.) in grazed pastures is generally regarded as inadequate. A selection of cultivars were compared in a small plot trial which was managed at contrasting grazing frequencies for 2 years and in which yield, height, and tiller numbers were measured. The whole trial was grazed regularly during the next 5 years and persistence determined as the proportion of timothy in the herbage harvested 6 and 7 years after sowing. The pasture type was more prostate and tillered than ‘Grasslands Kahu’. However, Kahu and the selection within Kahu were the highest yielding and Kahu was the most persistant. The low persistence of the prostrate type is discussed and partly attributed to its poor adaptation to New Zealand conditions.

Grazing dynamics of cattle stocked at heavy rates in a continuous and rotational grazed system

The relationships between grazing patterns of cattle and sward characteristics under two divergent grazing methods, continuous (CG) and rotational (RG) grazing, were determined in grassland sites of a Post Oak ( Quercus stellata) woodland in Texas from April to November 1981. Year-long rate of stocking in both grazing methods was equivalent at 50% above levels normally used to sustain stock without winter hay. Grazing time per unit area and grazing frequency on 0.1-ha plots within 3 grassland sites in each grazing regime were measured over a 7-month growing season using time-lapse photography. The pasture characteristics measured included forage standing crop and percentage of area grazed. Grazing system did not effect standing crop until the latter half of the growing season, when animals in the CG reduced grazing time on observed communities and used alternative habitats. Animals on RG grazed on 0.1-ha grassland sites 2–3 days per month while similar CG grassland sites were grazed 8–16 days per month at 3–6 day intervals. When grazed, the RG grassland sites experienced approximately 3 times more daily grazing events than CG with each grazing event varying from 55±11 to 345±31 animal-minutes and from 35±7 to 76±13 animal-minutes in RG and CG, respectively. The RG grassland sites received 4–21 and 21–35 more animal-hours per month in the first and second halves of the growing season, respectively, than CG. Care must be exercised in designing RG systems to ensure that grazing on seasonally preferred habitats can be controlled to allow strategic access to nutritionally critical habitats.

Demographic Responses of Bromus Tectorum and Seedlings of Agropyron Spicatum to Grazing by Small Mammals: The Influence of Grazing Frequency and Plant Age

(1) The influence of Microtus montanus (Cricetidae) grazing on the population biology of the annual Bromus tectorum and on seedlings of the perennial Agropyron spicatum was investigated using four grazing frequencies (grazed weekly, biweekly, monthly, or once) and ungrazed controls and was initiated at four plant ages (7, 30, 90 and 150 days old) in an unheated glasshouse experiment. (2) In both species, the proportional survival of individuals rose with decreased frequency of grazing and with increased age at initial grazing. (3) The age-by-species interaction for survival showed that B. tectorum increased survival from 17% for plants grazed at 7 days old to 69% for plants grazed at 30 days old or older. For A. spicatum survival remained at 5% when plants were grazed at 30 days old or younger but increased to 57% as grazing was delayed until plants were older. (4) The frequency-by-species interaction for survival showed a decline to 53% survival for B. tectorum that were grazed weekly whereas less frequent grazing resulted in 65% to 75% survival. For A. spicatum, weekly and biweekly grazing resulted in 11% survival, whereas survival increased to 40% with less frequent grazing. (5) Frequency of grazing and age at initial grazing had no significant effects on seed production of Bromus tectorum (P = 0 55 and P = 0 12).

Partitioning Herbivory and Its Effects on Coral Reef Algal Communities

Coral reef herbivores were classified into three functional groups according to criteria describing the frequency and intensity of disturbance to the algal community created by their herbivory. These herbivore groups included: microherbivores, which have small foraging ranges (1—100 cm2) and a high frequency of grazing any point within their range; the echinoid Diadema antillarum, which has intermediate—size foraging ranges (0.5—1 m2) and intermediate frequencies of grazing any one area within an individual's range; and herbivorous fishes, with large foraging ranges (up to 0.5 ha) and the lowest grazing frequencies at any one site. Algal communities on experimental coral—settling plates were subjected to treatments designed to detect the effects of grazing by representatives of each functional herbivore group on algal biomass, community structure, and primary productivity in a backreef/reefcrest habitat in St. Croix, United States Virgin Islands. Abundances of microherbivores and herbivorous fishes (mainly juvenile scarids) fluctuated over time, while Diadema antillarum abundance remained relatively constant. Grazing intensity (as measured by the rate of algal biomass removal and algal standing crop under different grazing regimes) was greatest for D. antillarum; grazing by D. antillarum resulted in low—biomass, highly productive algal turfs (O2 release per unit chlorophyll a per unit time: 11.3—22.4 mg · mg—1 · h—1). Algal turfs grazed by D. antillarum were dominated by epilithic and endolithic filamentous and crustose species. Grazing by herbivorous fishes led to algal communities with algal turfs of higher biomass than in D. antillarum—grazed treatments; these communities became dominated by a single algal species (Sphacelaria tribuloides). Fish—grazed algal communities had lower biomass—specific productivity rates than algal turfs grazed by D. antillarum (2.4—8.4 mg · mg—1 · h—1). Microherbivore—grazed and ungrazed treatments had the lowest biomass—specific productivity rates and eventually became dominated by a few macroalgal species. Although algal biomass in sea urchin—grazed treatments was only 25—50% of the biomass values in treatments not grazed by sea urchins, productivity per unit area was not significantly lower in the former treatments, suggesting a positive effect of sea urchin grazing on algal productivity. This positive effect is a result of the reduction of algal self—shading when grazing is intense and/or the input of regenerated nutrients from D. antillarum excretions. Coral reef plant—herbivore interactions are similar to those in terrestrial grassland—herbivore systems. As in many terrestrial systems, plant—herbivore interactions result in higher overall ecosystem primary productivity and apparently facilitate the flow of energy and materials in this case from the highly productive algal turf component to higher levels in the reef trophic web.

Factors affecting the productivity of irrigated annual pastures. 2. Defoliation by dairy cows

The influence of grazing intensity on the productivity of an irrigated annual pasture was studied for 3 years in northern Victoria. Lax-, medium- and hard-grazing intensities were described by post-grazing pasture heights of 7.2, 5.2 and 3.0 cm, respectively. Also, one instance of variable grazing frequency occurred, in winter of year 1. Hard-grazed plots produced 1 3 and 17% less herbage in years 1 and 2, respectively, than did lax- and medium-grazed plots, which produced similar amounts of herbage. When the interval between grazings was extended, the variation in productivity was reversed; lax grazing resulted in 9% less total production than heavier grazing. In years 1 and 2, there was little effect of grazing treatment on botanical composition until spring, at which time there was a marked reduction in the amount of subterranean clover (Trifolium subterraneum) in the hard-grazed plots, with a concomitant increase in grass content. There were no significant effects of grazing intensity on the amounts of weeds in either year. However, in year 3, weeds were important contributors to pasture production early in the season. This, together with reduced clover seed reserves and increased incidence of disease in subterranean clover with hard grazing, suggests that the long-term regenerating ability of an annual pasture may be impaired if severely grazed at regular intervals.

Effects of Jackrabbit Grazing, Clipping, and Drought on Crested Wheatgrass Seedlings

The effects of black-tailed jackrabbits on crested wheatgrass (Agropyron desertorum) seedling establishment and utilization were monitored on a mesic and 2 xeric Wyoming big sagebrush (Artemisia trdentata spp. wyomingensis) sites in Nevada. Although jackrabbit densities (1.4 to 2.9/ha) and utilization were high, seedling survival was not significantly different (p?0.05) inside or outside rabbitproof exclosures even on the xeric sites during drierthan-normal springs. Seedling density was greater on the mesic than xeric sites, but good grass stands were produced on all sites. The smaller seeded areas (less than 60 ha) and the edge of the large seeded area (400 ha) had the greatest forage utilization by rabbits. To determine the effects of defoliation and drought on seedling survival, seedlings in small tubes (3.8 cm diameter and 20 cm deep) and in large tubes (10 cm diameter and 1 m deep) were watered and clipped at 7 different intervals. Seedlings grown in the smaller volume were more sensitive to clipping and drought than those grown in the larger soil volume. Seedlings watered less than weekly showed a trend toward higher survival when clipped every 3 or 4 weeks than when clipped more or less frequently. Clipping weekly and watering less than weekly greatly reduced root growth and seedling survival. Although infrequent grazing by rabbits could slightly increase seedling survival in a dry year, the additive effects of frequent grazing and drought could result in stand failure, especially on shallow or rocky soils with a small soil volume that limits water retention and root growth. Rangelands of western North America are inhabited by several species of hares of the genus Lepus, commonly known as jackrabbits. The black-tailed jackrabbit (Lepus californicus) is probably the most abundant and widely distributed of the jackrabbits and therefore, most generally responsible for damage to crops and forage plants. Jackrabbit populations are very cyclic and virtually every western state has gone through severe crop depredation during population peaks (McAdoo and Young 1980). Large populations of jackrabbits have been considered a result and symptom of overgrazed rangelands (Fichter 1952) and a threat to crested wheatgrass seeded for range improvement (Goodwin 1960). High consumption of range forage by jackrabbits has been well documented (Taylor et al. 1935, Currie and Goodwin 1966, Westoby and Wagner 1973). Although Westoby and Wagner (1973) suggested and Goodwin (1960) observed that jackrabbits affected crested wheatgrass seedling establishment, these effects have not been quantified. McGinnies (1973) showed that clipping crested wheatgrass seedlings to ground level once during the 5month period following germination can reduce seedling survival by 50%o. However, for many years and clipping dates, clipping caused little or no seedling mortality, while for other years and clipping dates, high mortality was observed. Cook and Stoddart (1953) suggested that crested wheatgrass clipped early in the season would not produce regrowth under arid conditions. Mohammad et al. (1982) found 40% defoliation increased production of crested wheatgrass grown at -0.5MPa water potential while 80% defoliation resulted Authors are range scientist, formerly with USDA/ ARS, Reno, Nev., now at School of Renewable Natural Resources, University of Arizona, Tucson 85721; range agronomist, formerly with University of Nevada, Reno, now at Department of Crop and Soil Science, University of New Mexico, Las Cruces; wildlife scientist, Renewable Resources Center, University of Nevada, Reno; and range scientist, USDA/ ARS, Reno, Nev. Manuscript accepted March 19, 1985. in 100% mortality of plants at -l.5MPa water potential. The purpose of this study was to determine the effects of black-tailed jackrabbits and clipping on crested wheatgrass seedling survival in relation to precipitation.

Grazing management influences on seasonality and performance of ryegrass and red clover in a mixture

Grazing management influences on the production and species composition of a ryegrass, red and white clover pasture were evaluated over 3 years. Pastures were grazed by cattle frequently in either winter or summer and infrequently for the remainder of the year or grazed infrequently all year. Frequency was determined by the height of herbage pre-grazing and was lo-12 cm for frequent grazing and 15-20 cm for infrequent grazing. Annual herbage production of 15.1 t DM/ha was not influenced by grazing management but seasonal production was. Management caused both instantaneous and longer term effects on production of component species. Lower summer production because of frequent grazing in that season resulted from a reduction in red clover production from 2.75 to 1.3 t DM/ha. However, ryegrass production in spring was increased by 60% and in summer it was more than doubled by this grazing treatment. Frequent grazing in winter also increased ryegrass and reduced red clover production in summer compared with infrequent grazing all year but had no effect on ryegrass production in spring. Red clover plant density was unaffected by the different grazing managements imposed for two and a half years but subsequently was lower under frequent summer grazing. Red clover dominance in summer and its effect on ryegrass production in spring can be controlled by more frequent grazing in summer and a more even species balance results. Emphasis on spring or summer production can be achieved through grazing management without affecting total production. Keywords: Red clover, ryegrass, grazing frequency, cattle grazing, herbage production, seasonal production

EFFECT OF SHEEP GRAZING REGIME ON PERFORMANCE OF MATUA PRAIRIE GRASS

Persistency and productivity of irrigated 'Grasslands Matua' prairie grass pastures were measured under four sheep grazing regimes, frequent or infrequent (grazed 3 weekly or 6 weekly) coupled with lax or severe defoliation (grazed to 7.5 cm or 2.5 cm). Matua was also compared with 'Grasslands Nui' and Yates 'Ellett' perennial ryegrasses under frequent severe grazing. These are interim results from two experiments sown in successive years. There were few consistent differences among grazing treatments of Matua pastures. However, the Matua content of pastures tended to be less under frequent grazing. In the third year of Experiment 1, infrequent grazing to 2.5 cm resulted in significantly hlgher annual production than other Matua treatments. 'Eiiett' ryegrass tended to outyield 'Grasslands Nui' in the first year but subsequently there was little difference in yields. The dry matter production of 'Ellett ryegrass was not significantly different from the best Matua treatment in any year. More herbage was lost through trampling and decay in the infrequently grazed Matua pastures than in the frequently grazed Matua or ryegrass pastures. After three years, all Matua pastures contained more weeds and more volunteer grasses than did ryegrass pastures. Keywords: prairie grass, Matua, ryegrass, Nul, Ellett, grazing management, lax grazing, severe grazing, irrigation.

A simulation model for managing perennial grass pastures. Part I—structure of the model

A simulation model has been structured to facilitate stochastic evaluations of grazing management systems on perennial grass pastures. The output data, stored in a direct-access data set, can be used as input to statistical programs which will perform desired statistical analyses of the data. The model was originated to provide a practical method for estimating the effects of grazing frequency, duration, and grazing rate on the performance of grazing systems for perennial grass pastures. The model provides 32 different attributes for characterizing the performance of a grazing system.

A mechanistic simulation analysis of water use, leaf angles, and grazing in East African graminoids

A simulation model was constructed in order to interrelate the effects of defoliation by large mammalian herbivores with growth, photosynthesis, water use and light interception of representative graminoid vegetation from East Africa. Abiotic submodels describing water flows, light penetration and interception, and energy balance relationships were interfaced with a graminoid growth model that was specifically designed to examine grazing responses. Defoliation reduced rainfall interception and reduced transpiration, thereby increasing soil and plant water levels. Morphological adaptations made compensatory shoot growth possible, but grazing effects on plant water contents largely determined the degree of compensatory growth. Aboveground productivities were greatest at moderate grazing intensities while belowground productivities were greatest at lower grazing intensities. The success of a given water use strategy depended on simultaneous consideration of the abiotic environment and grazing. Under frequent grazing soil water conservation and reduced shoot/root ratio counteracted the depletion effect of high stomatal conductance on plant water content. Consequently photosynthesis under frequent grazing was maximized by higher stomatal conductance. Canopy geometry was adaptive for maximal light harvesting subject to the constraints imposed by transpiration, water availability, and herbivory. Total photosynthesis was increased greatly by erect leaf angles for all but not short grasses. For frequently grazed short-grasses the benefits of prostrate leaves associated with escape from grazing exceeded the associated costs of reduced photosynthate.

Grazing cycle length and silage supplementation: effects on the performance of lactating ewes with twin lambs

AbstractMasham ewes, stocked at 20 ewes ha−1, reared twins at pasture in 1979 and 1980 and were rotationally grazed around six paddocks. There were three lengths of grazing cycle (18, 30 or 42 d) and the ewes at pasture were either offered silage ad libitum (S) for 8 weeks of lactation or they were not supplemented with silage (N). By feeding silage, S ewes and lambs moved into greater herbage masses (3735 u. 3390 kg organic matter (OM) ha−1), but there was little effect on net herbage accumulation (10.5 v. 10.0 t OM ha−1) and herbage intakes per ewe were similar (2.31 v. 2.27 kg OM d−1) over the 7‐month grazing season. During the period of silage supplementation, total intake was 19% higher for S than N ewes, lamb growth rates were slightly higher (280 v. 273 g d−1) and the ewes lost less weight (−78 v−96 g d−1).For 18‐, 30‐ and 42‐d grazing cycles respectively the herbage masses before grazing were 2825, 3620 and 4240 kg OM ha−1; net herbage accumulations were 9.8, 10.4 and 10.6 t OM ha−1; mean daily herbage intakes by each unit (ewe+lambs) were 2.22, 2.35 and 2.30 kg OM and lamb growth rates from birth to weaning at 20 weeks were 205, 204 and 204 g d−1.Frequent grazing of relatively light herbage masses or infrequent defoliation of heavier herbage masses made little difference to sward or animal performance. It is concluded that, at this stocking rate, different grazing cycles of 18, 30 or 42 d do not affect the performance of lactating ewes.

Simulation study of east-African perennial graminoid responses to defoliation

The responses of East African grasses to defoliation at specific heights and frequencies were simulated mathematically over a single optimal growing season. The simulation model used morphological and physiological features of graminoid growth that are known to affect responses to defoliation. Water and nutrient limitations were not considered. Except under the most severe defoliation regimes, the model simulated greater aboveground and belowground productivities in grazed plants than ungrazed plants. This simulation of productivity was maximal at moderate grazing intensities, declining at both high and low grazing intensities. Short, mid, and tall-grasses exhibited different responses to defoliation. Short-grasses gave greater yields with greater frequencies of defoliation than mid and tall-grasses. Since mid and tall-grasses maximized their production through increased shoot sizes, greater intervals between grazing events were necessary. Short-grasses maximized production through increased shoot numbers, hence maximum yields could be obtained with greater grazing frequencies. At greater frequencies and lower heights of defoliation the proportions of blade tissue increased, stems decreased, nitrogen contents increased and a dense, leafy concentration of live shoot biomass was induced by enhanced tillering, removal of culm meristems and prevention of senescence. The most important factors responsible for grazing stimulation were: stimulation of tillering through decreased self shading, continued activity of non-elevated tiller meristems which had escaped grazing removal, release from apical dominance and subsequent stimulation of tillering, and the presence of a high maximum photosynthetic rate which rapidly replenishes carbohydrate reserves used for the early regrowth. The three essential properties a plant must have in order to compensate for herbivory are: (a) the ability to protect and regenerate apical meristems; (b) the ability to store carbohydrates that can supply activity of these meristems following substantial leaf area reduction; and (c) a photosynthetic rate great enough to support continued shoot and root growth, and to replenish carbohydrate reserves. Stimulation of photosynthetic rate by defoliation contributes greatly to the latter requirement.

Defoliation of ryegrass‐dominated swards by sheep

AbstractPatterns of defoliation in perennial ryegrass‐dominated swards were examined in two experiments. In Experiment I measurements were made on four swards after a single overnight grazing. In Experiment 2 observations were made repeatedly on marked tillers in two continuously stocked swards which were grazed down over a 24‐d period. In both experiments the chance of defoliation was related to lamina height both within and between age classes. Lamina angle was measured in Experiment 2 and within age classes the chance of defoliation was also independent of lamina angle. In Experiment 1 tillers most frequently had both of the two youngest laminae grazed; in Experiment 2 tillers with only lamina 1 grazed occurred most frequently, but defoliation of the two youngest laminae was again common.The different frequencies of grazing of the different classes of laminae is interpreted as being a function of their frequency of occurrence within the grazed layer at the top of the sward. The pseudostem apparently restricted the depth of the grazed layer in the very short swards of Experiment 2.Grazing behaviour in relation to sward structure and the patterns of defoliation and their implications for herbage production are discussed.