A PORTABLE-CORRAL TECHNIQUE FOR MEASURING THE EFFECT OF GRAZING INTENSITY ON YIELD, QUALITY AND INTAKE OF HERBAGE

A grazing experiment using four stocking rates of sheep, equivalent to 34, 45, 57 and 68 sheep/ha on an assumed 200-day grazing season, was conducted using a portable grazing corral technique. Plots were subjected to fotir grazing periods between mid May and early September. The effect of stocking rate on herbage yield and quality and the influence of these factors and feed intake on liveweights of the sheep were recorded. The mean daily herbage organic matter available over the trial was 9.6, 5.8, 3.3 and 23% of the total liveweight of the sheep at each of the four stocking rates. The highest grazing pressure led to the production of high-quality herbage, but also led to reduced productivity, low feed intake and liveweight losses. The most lenient grazing pressure failed to provide adequate herbage utilization. Even at the most intensive stocking pressure, only 66% of the herbage available to ground level was utilized in grazings after July. Intake results suggested that sheep of 45 kg liveweight required 1000–1200 g digestible organic matter per day to maintain body weight. Despite the higher in vitro digestibility of herbage on offer at the higher stocking rates, intake was limited through lack of herbage; a high degree of correlation existed between herbage availability and herbage intake over the four stocking rates and at all grazings. It is concluded that the portable corral technique is well suited for grazing studies and the assessment of sward response to varying stocking rates and is particularly useful where facilities for more extensive studies are limited.     

Effect of altering the grazing interval on growth and utilization of grass herbage and performance of dairy cows under rotational grazing

The effects of short grazing intervals in the early part of the grazing season on the growth and utilization of grass herbage, and the performance of grazing dairy cows, in a rotational grazing system were examined. Seventy-six cows were allocated to two grazing treatments: a normal rotation treatment (20-d rotations for the first 60 d) and a short rotation treatment (12-, 8-, 8-, 8-, 12- and 12-day rotations). Thereafter, both treatments had the same grazing interval and over the season as a whole both treatments received the same amount of nitrogen fertilizer and were stocked at the same rate. The short rotation treatment significantly reduced pre- and post-grazing sward heights and pre-grazing herbage mass in May and June. Total herbage production was significantly lower on the short than the normal rotation treatment as a result of a significant reduction in the growth rate of herbage in May and June. The short rotation treatment had a significantly lower milk output per cow. Grazing shorter swards, as a result of shorter rotations, significantly reduced herbage intake, reflecting reductions in intake per bite, grazing time and total bites per day. Treatment had no significant effect on herbage quality or pre- and post-grazing sward height in August and September, despite the increased grazing severity in May and June with the short rotations. The severity of rotation length in this instance had a detrimental impact on animal performance, whereas a more modest reduction in grazing interval may control herbage production, without reducing animal performance.     

Out-of-season management of grass/clover swards to manipulate clover content

Two experiments are described in which the effect of grazing or defoliating mixed swards at different times over winter and spring on clover content and development was investigated. In the first experiment swards were grazed with sheep (to about 3 cm) for a short period in (a) November, (b) November, January and March, (c) March or (d) not at all, in three consecutive years. All swards were grazed intermittently during the grazing season with cattle and cut for silage once each year. Each plot received either 0 or 50 kg N ha^?1 in March. The effect of N fertilizer was to reduce clover content in each summer and clover growing point density in the third year. In two of the three years, treatments involving grazing in March had lower subsequent net annual herbage accumulation compared with the other two treatments and higher clover content in summer of the third year. Reduction in growing point density in all plots during the grazing season was associated with cattle grazing when conditions were wet, suggesting that stolon burial was implicated. Grazing with sheep in November, January and March resulted in significantly more visible (when counted in situ) clover growing points in April in year 2 and more total growing points (counted after dissection of turves) in the third year than the November grazed and ungrazed treatments which had, on occasions, higher grass tiller density. In a microplot experiment, high herbage mass standing over winter was associated with lower potential photosynthesis per unit clover lamina area and lower growing point density in March. Cutting herbage in March to 2-3 cm resulted in higher clover content and higher growing point number per unit stolon length. The latter was significantly correlated with total irradiance and red: far red at the canopy base. Potential photosynthesis of clover was not affected by cutting in March. It is concluded that growing point density can be increased by grazing or cutting during winter or spring. However, in order for these new stolons to contribute to clover yield during the summer, they have to be maintained until then by ensuring that competition from grass is minimized by keeping the sward short in winter and spring and avoiding the burial of stolons during grazing.     

Effects of cattle grazing on herbage quality in a herbaceous Mediterranean rangeland

The main objective of this study was to determine to what extent grazing pressure and timing modulate the seasonal progression of herbage quality in hilly Mediterranean grassland systems. The study was conducted during six consecutive years between 2003 and 2008 at the Karei Deshe experimental farm, in eastern Galilee, Israel, dominated by rich hemicryptophytic grassland. Treatments included two different grazing intensities, heavy and moderate, with 1·1 and 0·55 cows ha^?1, respectively, and management that included a continuous and a seasonal stocking system that was divided at both intensities into early and late grazing. Herbage samples were analysed for digestibility, crude protein, neutral detergent fibre and acid detergent fibre contents. Significant differences in herbage quality were found between seasons and years. Herbage quality was significantly higher in paddocks grazed continuously or early in the season. Herbage quality increased with increasing grazing intensity as younger herbage and continued re‐growth were maintained during the green season. The greater difference between herbage qualities was found at the peak of the growing season. The significant differences found in herbage quality emphasize the importance of the decision‐making process aimed at improving cattle grazing management in Mediterranean rangelands and its consequences for the sustainability of the system.     

GRASSLAND SYSTEMS*

Reference is made to the contrast between actual and potential yields from grassland, to the main factors affecting the development of effective grassland systems for dairy cows and to the technical developments which are now available. The unrealized potential for simplification and increased output from grazing systems is stressed. The available information on the effect of mechanical grazing and storage feeding systems is reviewed and the practical advantages and problems of these systems summarized. Simple calculations are made of the capital involved in large herd organization and the increases in herbage yield or efficiency of use needed to justify this additional expenditure. For large herds a relatively small increase (10%) in output per acre would justify the annual capital charge and feed cost for mechanical harvesting or tower silage; greater increases would be needed for grass drying (22%) or for tower silos in smaller (100-cow) herds (16%). Other important but less tangible factors influencing the choice of system are referred to. It is considered that unless herbage yields can be greatly increased by the use of mechanical grazing compared with normal grazing, the practical difficulties of this method outweigh its advantages. If tower silos allow more efficient conservation and easier feeding, they may be worthwhile, but the search should continue for cheaper alternatives. Only in very large-scale enterprises can grass drying, solely to produce cattle feed, be justified, although this method offers the greatest potential. In view of the complexities, it is suggested that computer models may help to resolve such problems and one such study is briefly described.     

An evaluation of the effects of grazing management systems involving preferential treatment of high-yielding dairy cows on animal performance and sward utilization

Two systems of grazing management involving preferential treatment of high- yielding dairy cows were compared with a grazing system in which both high- and low-yielders received uniform treatment. Cows were rotationally grazed across I-day paddocks without concentrate supplementation from 23 April to 8 October 1985, with a mean stocking rate over the season of 5-4 cows ha^?1. Preferential treatment of high-yielding cows was achieved either by using a leader/follower approach (LF) with high-yielding cows in the leader group, or by preferential forage feeding (PFF) where high-yielding cows were allowed access to grass silage for 1 -5 h daily and grazed alongside low-yielders. Control (C) cows grazed together as a single group. The high grazing stocking rates used on all three treatments resulted in good grass utilization with residual sward heights, assessed by a rising-plate sward stick, of 45, 50 and 48 mm for the LF, PFF and C treatments respectively. Animal performance data for the LF, PFF and C treatments respectively were: milk yield (kg d^?1) 15middot;1, 15middot;6 and 14middot;7 (s.e. 0middot;78); milk fat yield (g d^?1) 598, 606 and 567 (s.e. 34); milk protein yield (g d^?1) 500, 519 and 480 (s.e. 31); and live weight gain (kg d^?1) 0middot;12, 0middot;23 and 0middot;25 (s.e. 0·05). These results indicate that leader/follower grazing had little overall effect on animal performance when high grazing severity was imposed, with the improvement in animal performance of high-yielding cows in the leader group being offset by the reduced performance of the follower group. Buffer-feeding of high-yielding, rotationally-grazed cows with high-quality grass silage had little effect on animal performance and resulted in a decrease in the efficiency of grassland utilization. Silage appeared to substitute for herbage, with a reduction in herbage DM intake of 0middot;55 kg per kg silage DM consumed.     

Forage availability from a temperate pasture managed with intensive rotational grazing

Successful integration of rotational grazing into livestock production systems requires estimates of pasture growth rates for feed budgeting of daily animal intake. By matching livestock nutrient demand with forage availability, over-feeding of supplements can be minimized, which reduces feed costs and the need lo manage surplus nutrients, A three-year grazing study was carried out on a Kentucky bluegrass ( Poa pratensis L.)-dominant pasture to estimate the daily quantity of herbage available to cattle in an intensive, rotational grazing system. Herbage production, species composition, and forage quality were determined in each of the six grazing cycles in a year, from April until September. The average length of a grazing cycle was 28·6 d, with 2·7 d for duration of grazing on a paddock. Pre-grazing and post-grazing sward heights, measured with a plate meter, were 14 and 7 cm, and the corresponding herbage masses were 1955 and 775 kg DM ha⁻¹ respectively. Under adequate soil moisture during 1989, herbage available for daily intake was 53 kg ha⁻¹ from April until mid- August, declining to approximately 32 kg ha⁻¹ d⁻¹ by the end of September. Distribution of this herbage was fairly uniform until the end of August. However, a dry summer in 1991 reduced herbage availability to 15 kg ha⁻¹ d⁻¹. Bluegrass and white clover ( Trifolium repens L.) formed 70% of the herbage yield during the period April–June. Later in the season, dead matter and other species increased, reducing the contribution of bluegrass and clover to approximately 60% of total dry matter. While these pastures have the potential to provide significant amounts of forage for 5–6 months in a year, additional on-farm forage reserves are needed during periods of water stress.     

The use of conserved forage as a supplement for grazing dairy cows

The difficulty in matching the herbage requirements of grazing dairy cows to herbage production, due mainly to the unpredictability of the latter., causes stocking rates to be too low for maximum per hectare production and, thus, cows to be underfed at certain times in the grazing season. Conserved forage may be used as a supplement for grazing dairy cows in order to reduce variation in forage intake by the cow, to allow pasture stocking rates to be increased and to increase the efficiency of land use. The effect of offering conserved forage with herbage on intakes and production is reviewed in comparison to both ad libitum and restricted herbage. Total nutrient intakes and milk fat + protein yields are reduced for cows offered herbage and supplementary forage compared with cows offered ad libitum herbage, but increased compared with cows offered a restricted herbage level. Increasing pasture stocking rates may allow increases in utilized metabolizable energy levels from grassland but further research is needed in this area. Both grass and maize silage supplements offer potential for increasing the efficiency of land use, but in the case of grass silage this is only achieved in the best management practices.     

Modelling the concentrations of nitrogen and water-soluble carbohydrates in grass herbage ingested by cattle under strip-grazing management

There is scope of increasing the nitrogen (N) efficiency of grazing cattle through manipulation of the energy and N concentrations in the herbage ingested. Because of asymmetric grazing by cattle between individual plant parts, it has not yet been established how this translates into the concentrations of N and water‐soluble carbohydrates (WSC) in the herbage ingested. A model is described with the objective of assessing the efficacy of individual tools in grassland management in manipulating the WSC and N concentrations of the herbage ingested by cattle under strip‐grazing management throughout the growing season. The model was calibrated and independently evaluated for early (April), mid‐ (June, regrowth phase) and late (September) parts of the growing season. There was a high correlation between predicted and observed WSC concentrations in the ingested herbage (R² = 0·78, P < 0·001). The correlation between predicted and observed neutral‐detergent fibre (NDF) concentrations in the ingested herbage was lower (R² = 0·49, P < 0·05) with a small absolute bias. Differences in the N concentration between laminae and sheaths, and between clean patches and fouled patches, were adequately simulated and it was concluded that the model could be used to assess the efficacy of grassland management tools for manipulating the WSC and N concentrations in the ingested herbage. Model application showed that reduced rates of application of N fertilizer and longer rotation lengths were effective tools for manipulating herbage quality in early and mid‐season. During the later part of the growing season, the large proportion of area affected by dung and urine reduced the effect of application rate of N fertilizer on herbage quality. In contrast, relative differences between high‐sugar and low‐sugar cultivars of perennial ryegrass were largest during this period. This suggests that high‐sugar cultivars may be an important tool in increasing N efficiency by cattle when risks of N losses to water bodies are largest. The model output showed that defoliation height affects the chemical composition of the ingested herbage of both the current and the subsequent grazing period.     

Herbage growth and utilized output from grassland on dairy farms in southwest England: case studies of five farms, 1982 and 1983. II. Herbage utilization

Utilized Metabolizable Energy output was calculated and herbage utilization evaluated in two contrasting years on five profitable farms representing a range of soil types.
Annual UME output was 72 GJ ha^-1 on average, with a range from 47 to 91 GJ ha^-1. Grazed grass provided 66% of the utilized metabolizable energy, and conserved grass 34%. Higher utilized metabolizable energy output was not always obtained at higher fertilizer N inputs, even when soil moisture conditions favoured herbage growth.
The efficiency of utilization of herbage conserved (almost always as silage rather than hay) was calculated by expressing utilized metabolizable energy output as a proportion of the quantity of herbage cut, measured by swath weighings; the mean value was 64%, with a range from 55 to 73%. Cellulose analyses indicated that mean dry matter losses via CO₂ and effluent were 10%; the remaining 26% loss appeared to be due to physical losses in the field, surface waste and wastage at feedout.
For grazed herbage the utilized metabolizable energy output was expressed as a proportion of herbage accumulation measured over 28-day periods. The resultant apparent efficiency of utilization averaged 67%, with a wide range from 51 to 83%. The lowest values were on badly drained farms.
It is suggested that:
(i) there is considerable potential for increasing output from grazing on dairy farms; higher grazing pressure and more flexible management would be needed. Targets should probably be set lower on badly drained soils;
(ii) there is great potential for increasing the efficiency of utilization of conserved forage, by careful application of existing technology;
(iii) on the farms studied the utilized metabolizable energy output from grazed and conserved fields appeared to be similar.     

STUDIES OF THE GROWTH OF A HYP ARRHENIA-DOMINANT GRASSLAND IN NORTHERN RHODESIA

The results of studies preliminary to management trials on this type of grassland are reported. The annual growth cycle of the community is described in terms of herbage yields and chemical composition. It is shown that repeated cutting at an early growth stage will prevent the rapid deterioration in quality of the herbage which is evident in the uninterrupted growth cycle. Changes in the sward with repeated cutting are described.
The second phase of growth, after the main flush has flowered and set seed, may be enhanced by cutting in the second half of the wet season; it is suggested that this aftermath growth might be used for grazing in the first part of the dry season.
The annual growth cycles cf six component species of the community grown as pure stands are described, together with the yields and chemical composition of the herbage obtained from them with repeated cutting.
The results of fertilizer trials on this type of grassland are given, and it is shown that substantial increases in yield of dry matter and percentage crude protein may be obtained with the application of sulphate of ammonia. Responses to dressings of superphosphate are largely conditional on alleviating the nitrogen deficiency, and there is a significant nitrogen/phosphorus interaction. Both marinate of potash and agricultural lime have little effect on growth and production at the levels tested.
Investigation of the practice of burning the grassland in the late dry season, after resting from grazing in the previous wet season, confirms that this is an effective means of checking the encroachment of woody species, but the flush of new grass growth induced by the fire is of such small bulk as to be of no importance in grazing management.     

FURTHER OBSERVATIONS ON GRASSLAND MANAGEMENT FOR MEAT PRODUCTION

This paper deals with the second three years (April 1954 to March 1957) of a grazing-management trial in the form of a pilot farm. The whole area of 35.5 acres was run as a self-contained unit with the object of providing grazing for as long a period of the year as possible. A system of rotational grazing was used throughout with strip- and fold-grazing at certain seasons. Excess herbage was conserved as silage and hay and fed back to stock during the winter. Beef-type steers and ewes and lambs grazed the pastures, the saleable products being fat cattle, lambs and wool. Results are presented and discussed in relation to stock numbers, animal health, herbage production and botanical composition, fertilizer application and the levels of production achieved. Over-all average fertilizer dressings per acre for the three years were equivalent to 5 cwt. per acre nitro-chalk, 2 cwt. per acre superphosphate and 1 cwt. per acre muriate of potash. The outputs of utilised starch equivalent in 1954–5, 1955–6 and 1956–7 were 2970, 2850 and 2280 1b. per acre, respectively. On the basis of the six years' results it is concluded that high production can be achieved from a system where the object is an extended grazing season; that broadcast leys can be used for winter grazing and the botanical composition of the sward maintained; that self-fed silage can be a satisfactory feed for fattening cattle; that a grazing plan is a valuable guide to management; and that the pilot-farm method is of value for certain agronomic experiments.     

FACTORS LIMITING ANIMAL PRODUCTION FROM GRAZED PASTURE*

Animal production from intensively managed pasture (240 units N/ac or 300 kg N/ha applied annually) should in theory reach 11,000 Ib/ac (12,500 kg/ha) of milk or 1550 lb/ac (1750 kg/ha) of liveweight gain per year. The figure for theoretical milk production is achieved in experiments, although rarely approached in commercial practice; the figure for liveweight gain is never approached, either experimentally or commercially. On commereial farms in Britain, the average stocking rate for grazed lowland pasture in 1971 was about 0·74 cow equivalents/ac (l±82/ha), compared with a theoretical target of 1·9/ac; in 1969 fertilizer N application was about 48 units/ae (60 kg/ha). The main purpose of this paper is to suggest reasons for the differences between practical, experimental and theoretical levels of production. Economic factors may deter farmers from intensifying their grassland management, but the deterrent to high stocking rates may be the fear of running out of grass. In practice, ungrazed herbage is used as a buffer, but other feeds might be used for this purpose. Concentrates, pelleted roughages and even long dried grass and silage are too attractive to grazing beef cattle to be offered to appetite; but silage might be used as a long-term buffer. Fouling of pasture reduces efficiency of harvesting, but attempts to overcome this effect, by conditioning of grazing animals, spreading excreta or by alternation of grazing and cutting, have largely been unsuccessful. High production per unit area cannot be achieved without high production per animal. Legumes have often been found to increase production per animal, and a technique has been developed for growing red-clover and grass in adjoining areas and grazing them together. The clover was grazed satisfactorily by dairy cows (and caused no bloat) but failed to increase milk yield per animal. Recent calorimetric studies of grass have shown that the net energy value of digestible organic matter is variable, and in particular is low for late-season herbage.     

Assessment of regional variation in climate on the management of dairy cow systems in Ireland using a simulation model

A dairy system simulator, Dairy_sim, was designed to assess the interactions between climate and management in spring‐calving milk production systems based on the grazing of grass pastures. The simulator comprises three main components: a grass herbage growth model, an intake and grazing behaviour model, and a nutrient demand model. The simulator was initially parameterized using the Irish National Dairy Blueprint. Sensitivity analysis indicated that the simulator was most sensitive to stocking rate, milk output per cow and nitrogen fertilizer inputs, but less sensitive to other variables. Field data from four grazing systems were used to test the simulator and it was concluded that Dairy_sim was suitable for evaluating the interaction of climate and management for rotational grazing dairy systems based on perennial ryegrass pastures with Friesian cows. The simulator, Dairy_sim, was then used to evaluate the effects of the regional climates of Ireland on system management. The results indicated that, between regions, herbage production at the same input of nitrogen may vary proportionally by 0·10 and that the length of the grazing season may vary by 0·25. It was concluded that the simulator could be a useful tool for developing region‐specific dairy production blueprints.     

The intake and feeding value for young beef cattle of two cultivars of tetraploid Italian ryegrass when grazed or conserved by artificial dehydration or ensilage

Two experiments were carried out to determine whether the differences in intake and feeding value previously shown between two grass cultivars when offered to ruminants as chopped artificially dehydrated (dried) material could also be demonstrated when the grasses were offered in other forms. Two cultivars of tetraploid Italian ryegrass ( Lolium multiflorum ), Sabalan and Tetila, were established in the same field in 1975. In 1976 they were grazed and conserved (two cuts of primary growth) as dried material or as silage.
The composition of the herbage selected at pasture and conserved showed higher concentrations of normal detergent fibre and acid detergent fibre in the dry matter for Tetila than for Sabalan, but differences between cultivars in digestibility were small. In both grazing and winter feeding trials differences in voluntary intake between the two cultivars were not significant, but at pasture young beef cattle spent less time grazing and tended to spend more time ruminating on Tetila than Sabalan. There was no measure of animal performance at pasture but liveweight gain was 15% higher for Sabalan than Tetila when both were offered to young beef cattle as the sole feed of dried grass or of silage. The voluntary intakes of the three forms of feed were very similar, which in part reflected a similarity in digestibility. However, gains were lower for calves given silage than those given dried grass. This may have been due to a lower efficiency in the utilization of the nitrogeneous components of silage for tissue growth than those of dried grass.     

Evaluation of a sward sampling technique for estimating herbage intake by grazing sheep

A sampling procedure for estimating herbage intake by the ‘Difference’ method over short grazing periods using an electrically powered sheep-shearing head to cut long narrow sample strips, was compared with several indirect animal techniques on single-variety grass swards. The method provided intake estimates in good general agreement with those obtained by animal methods but discrepancies arose when used on a semi-prostrate variety due, probably, to incomplete recovery of sampled herbage cut from post-grazing residues. It was concluded that the method might be usefully adopted for the preliminary assessment of the intake characteristics of herbage varieties in routine evaluation programmes, provided that care is taken to ensure the efficient collection of herbage sampled post-grazing and that a reduction in the land requirement can be achieved without undue loss of accuracy or precision. Confirmation of results should be sought using animal methods when possible.     

The effect of stocking rate and calving date on grass production,utilization and nutritive value of the sward during the grazing season

A 2‐year whole‐farm system study compared the accumulation, utilization and nutritive value of grass in spring‐calving grass‐based systems differing in stocking rate (SR) and calving date (CD). Six treatments (systems) were compared over two complete grazing seasons. Stocking rates used in the study were low (2·5 cows ha^?1), medium (2·9 cows ha^?1) and high (3·3 cows ha^?1), respectively, and mean CDs were 12 February (early) and 25 February (late). Each system had its own farmlet of eighteen paddocks and one herd that remained on the same farmlet area for the duration of the study. Stocking rate had a small effect on total herbage accumulation (11 860 kg DM ha^?1 year^?1), but had no effect on total herbage utilization (11 700 kg DM ha^?1 year^?1). Milk and milk solids (MS; fat + protein) production per ha increased by 2580 and 196 kg ha^?1 as SR increased from 2·5 to 3·3 cows ha^?1. Milk production per ha and net herbage accumulation and utilization were unaffected by CD. Winter feed production was reduced as SR increased. Increased SR, associated with increased grazing severity, resulted in swards of increased leaf content and nutritive value. The results indicate that, although associated with increased milk production per ha, grazed grass utilization and improved sward nutritive value, the potential benefits of increased SR on Irish dairy farms can only be realized if the average level of herbage production and utilization is increased.     

Regrowth, morphology and persistence of Grasslands Puna chicory (Cichorium intybus L.) in response to grazing frequency and intensity

Effects of different grazing frequencies and intensities on herbage production (on both a unit pasture and individual plant basis) and on persistence of chicory ( Cichorium intybus L. cv. Grasslands Puna) were studied at Palmerston North, New Zealand (latitude 40°23'S) from November 1994 to November 1995. Three experiments were conducted on the same chicory stand, sown on 12 May 1994. The main grazing experiment had two grazing intensities, hard-lax grazing (50- to 100-mm stem stubble to mid-January, and thereafter 100- to 150-mm stem stubble) and lax grazing (100- to 150-mm stem stubble), and three grazing frequencies (1-, 2- or 4-week intervals). A subsidiary plant survival experiment compared the survival of 120 marked plants in ungrazed and grazed treatments. A late autumn grazing experiment examined the effects on plant persistence in the following spring. The greatest herbage mass (leaf + stem) resulted from the 4-week grazing frequency [9640 ± 874 kg dry matter (DM) ha⁻¹], in which stem mass was reasonably low (1270 ± 410 kg DM ha⁻¹), but was significantly higher in the 4-week grazing frequency than 1- and 2-week grazing frequencies ( P < 0·01). Grazing intensity had no significant effect except on the average stem mass of individual plants when the hard-lax intensity gave a lower stem mass ( P < 0·01). There were no interactions between grazing frequency and intensity in herbage mass. Plant density declined by 35% over the growing season with the decline unaffected by grazing intensity or frequency during the season. Grazing in late autumn resulted in approximately 27% less plants the following spring. It was concluded that grazing management through the growing season cannot be used to improve persistence without compromising leaf growth rate, but that avoidance of grazing late autumn will improve the persistence of chicory.     

The effects of level of Molinia utilization on diet selection and herbage intake by cattle grazing Molinia grassland

Groups of mature, non-lactating, cows grazed two Molinia -dominant grassland communities in central and southern Scotland during six consecutive summers. Two treatments, designed to use either 33% or 66% of the estimated annual Molinia leaf production by grazing to different leaf lengths, were imposed at each site. Grazing was restricted to the period of Molinia growth each season. During the first 4 years, diet composition, diet digestibility and herbage organic matter intake were determined during either one or two measurement periods each year. There were differences between sites in the floristic content of the sward and these differences were reflected in the diet selected by the cattle. Cows grazing the taller (33% utilization) plots had higher percentages of Molinia , grass stem, sheath and inflorescences and lower percentages of broad-leaved grasses, sedges, rushes and dead herbage in the diet than those grazing the shorter (66% utilization) plots. Differences between the floristic composition of the sward and the diet were explicable by (a) the height at which cattle grazed in relation to the distribution of components within the sward or (b) the selective grazing of small areas dominated by a particular species. The organic matter digestibility of diets differed between sites but there was no significant difference in digestibility or organic matter intake between the treatments. On average less than 50 d grazing was provided by the experimental sites each year. During this period the liveweight gains of cows grazing the two treatments did not differ significantly. The implications of these results for the management of Molinia -dominant communities are discussed.     

SOME EFFECTS OF GRAZING MANAGEMENT ON THE YIELD AND ITS COMPONENTS OF SOME PASTURE GRASSES

A study was made to determine the effects of grazing to a height of 1 in. when the swards reached heights of 3 and 9 in. on the dry matter production, LAI, tillering and rate of leaf production of new and old tillers in the spring–summer and autumn–winter seasons of 3 pasture species growing in association with white and red clovers. In both seasons the herbage yield under 9–1 management was higher than that under 3–1 and was significantly greater in the spring-summer season. Differences in DM production between cocksfoot, tall fescue and Ariki ryegrass failed to reach significance.
Light utilization under the 2 management systems was considered to be inefficient. In the autumn-winter period there was a linear relationship between the LAI and DM production in all treatments.
The rate of leaf production per tiller was significantly higher in cocksfoot than in ryegrass and tall fescue in both seasons.
New tillers had a significantly higher rate of leaf production than old tillers in the spring-summer period, but not in autumn-winter. The numbers of grass tillers and rooted nodes of clover were significantly higher under 3–1 than under 9–1 and were influenced by season.