Sward Characteristics Research Articles

Effects of continuous sheep stocking and strategic rest periods on the sward characteristics of binary perennial grass/white clover associations

AbstractFive binary perennial grass/white clover (Trifolium repens, cv. Menna) mixtures were evaluated over a 3‐year period under continuous sheep stocking together with the imposition of a rest period for either an early or a late conservation cut; the experiment with plot sizes of 0·16 ha was replicated three times. The grass species and cultivars used were Merlinda tetraploid and Magella diploid perennial ryegrass (Lolium perenne), Prairial cocksfoot (Dactylis glomerata), Rossa meadow fescue (Festuca pratensis) and Goliath timothy (Phleum pratense). The greatest total lengths of white clover stolon developed in the meadow fescue (171·6 m m−2) and timothy (151·9 m m−2) associations compared with those in tetraploid perennial ryegrass (98·6 m m−2), diploid perennial ryegrass (91·9 m m−2) and cocksfoot (74·6 m m−2) (s.e.d. 16·4, P < 0·001). On average, the proportion of white clover stolon that was buried was between 0·86 and 0·89 and this was more abundant in late than early season. Whereas timothy persisted, the persistence of meadow fescue was low under any of the managements tested and this was markedly reduced by the third grazing season. In the diploid perennial ryegrass sward, a late June to early August rest period for conservation enhanced white clover stolon length. An early April to late May rest period greatly reduced total white clover stolon length in both diploid perennial ryegrass and tetraploid perennial ryegrass associations (diploid perennial ryegrass‐unrested 89 m m−2, early rest 56·1 m m−2, late rest 130·7 m m−2; tetraploid perennial ryegrass ‐ unrested 125·1 m m−2, early rest 71 m m−2, late rest 99·7 m m−2; s.e.d. 19·19, P < 0·001). The numbers of white clover stolon growing points per unit stolon length were greatest when the sward was rested during late June to early August −55·9 m−1 stolon length compared with 45·7 m−1 for an April to late May rest and 46 m−1 in the absence of a rest (s.e.d. 2·59, P < 0·001). Likewise, the percentage of stolon above ground was greatest with the late June to early August rest −15·78% compared with 10·61% for the April to late May rest and 7·69% for no rest (s.e.d. 1·569, P < 0·001). The complementary percentages of buried stolon indicate the important role this fraction has and the need to study stolon behaviour in grazing studies generally. It is concluded that, in relation to perennial ryegrass as a companion grass, meadow fescue and timothy allow better white clover development and cocksfoot less. However, other attributes have to be considered, for example the poor persistence of meadow fescue and the slower regrowth of timothy, both of which allow the invasion of weed grasses, or the lower acceptability of cocksfoot to livestock. The timing of the rest period before the conservation cut can influence white clover development considerably, but the effects differed with different companion grasses.

High and low resolution TM data for the assessment of herbage and sward characteristics in small fields

The smallfield pattern characteristic of the Northern Ireland landscape necessitates the use of high resolution remotely-sensed imagery in grassland studies. In August 1986, 5 m resolution ATM and 30 m resolution TM data was collected from a grassland area in Northern Ireland. Herbage mass, sward surface height and botanical characteristics were assessed for approximately 120 fields in the overfly area. Correlations between digital numbers (DN) in three wavebands for both resolutions from commonly sampled fields were poor as a result of small field size and poor overlap of pixel area sampled. Variability and error associated with ground data probably masked any effect of small field size. Height, mass and percentage dead matter were the sward variables predicted with most accuracy by DN but most correlations were low and 5 m resolution was better than 30 m resolution. Both sets of imagery appear to have more potential to improve and quantify grassland classifications rather than provide absolute values for useful sward parameters.

A comparison of diploid and tetraploid perennial ryegrass and tetraploid ryegrass/white clover swards under continuous sheep stocking at controlled sward heights. 3. Sward characteristics and animal output, years 4–8

Results for years 4–8 of a long‐term grazing experiment on swards of a diploid perennial ryegrass (Lolium perenne), var. Contender (D swards), a tetraploid ryegrass, var. Condesa (T swards) and Condesa with S184 white clover (Trifolium repens) (TC swards), direct sown in May 1987, are presented. The swards were continuously stocked with sheep from 1988 to 1990, as previously reported, and for a further 5 years, 1991–95, at a target sward surface height (SSH) of 4–6 cm. Control of sward height was successfully achieved by variable stocking, except in 1993 when paddocks were set stocked and the resulting mean SSH was 9·3 cm. Grass swards received on average 160 kg N ha−1 year−1; grass/clover swards were mainly not fertilized with N with the exception that they were given 30 kg N ha−1 as a remedial mid‐summer application during a period of low herbage mass on offer in 1994 and 1995.Mean white clover content of the swards fell from 18·2% of herbage dry‐matter (DM) in 1992 to 8·5% in 1993, whereas stolon lengths fell from 120 to 58 m m−2. A return to lower sward heights in 1994–95 resulted in an increase in white clover content to 12·8% by the final sampling in August 1995. Perennial ryegrass content of the grass swards remained high throughout (mean 96·7% in 1995). Perennial ryegrass tiller densities recorded in August 1991, 1993 and 1994 showed consistently significant (P < 0·001) sward differences (3‐year mean 16 600, 13 700 and 10 100 perennial ryegrass tillers m−2 for the D, T and TC swards). In 1994, the year after lax grazing, a low perennial ryegrass tiller density (9100 m−2) and low white clover content (mean 4·3%) in the TC swards resulted in a much lower herbage bulk density than in the grass swards (April–July means 72, 94 and 44 kg OM ha−1 cm−1 for the D, T and TC swards). There was a consistent 40 g d−1 increase in lamb liveweight gain on the TC swards over the T swards, except in 1994. In that year there was a reduction in lamb liveweight gain of 33 g d−1 on the TC swards and a significant increase in ewe liveweight loss (117 g d−1) associated with low herbage bulk density despite optimal sward height. Lamb output (kg liveweight ha−1) on TC swards reflected white clover content, falling from a similar output to that produced from grass given 160 kg N ha−1, at 18% white clover DM content, down to 60% of grass + N swards with around 5% clover. A 6% greater output from the T than the D swards was achieved mainly through higher stocking rate. The experiment demonstrated a rapid, loss in white clover under lax grazing, and showed that the relationship between performance and sward height is also dependent on herbage density. High lamb output from a grass/clover sward was only achieved when the clover content was maintained at 15–20% of the herbage DM.

Effect of grazing system, stocking rate and season of use on diet quality and herbage availability of alfalfa-grass pastures

A 3-yr field experiment was conducted (1991–1993) near Brandon, MB to determine the effects of continuous and rotational stocking, both at heavy (2.2 steers ha−1) and light (1.1 steers ha−1) stocking rates, and of season of use on nutritive value and sward characteristics of an alfalfa-grass pasture [approximately 70% alfalfa (Medicago sativa L.), 25% meadow bromegrass (Bromus biebersteinii Roem & Schult.) and 5% Russian wildrye (Psathyrostachys juncea (Fisch.) Nevski)]. Grazed herbage quality and herbage mass were determined concurrently on continuous and rotational stocking treatments several times each year, as animals entered and exited the 5th of 10 rotationally stocked paddocks. Grazing system and stocking rate did not affect (P > 0.05) dietary CP and IVDOM, except once (P < 0.05) for IVDOM in 1993. Both ADF and NDF were sometimes greater (P < 0.05) on heavy compared to light stocking rate treatments, but did not differ (P > 0.05) between grazing systems. As the 1991 season advanced, there was a decline (P < 0.05) in CP, but IVDOM, ADF and NDF remained unchanged (P > 0.05). In 1992, seasonal declines (P < 0.05) in CP and IVDOM and increases (P < 0.05) ADF and NDF were observed for all treatments. In 1993, in vitro digestible organic matter and CP decreased (P < 0.05) on most treatments, while ADF and NDF increased (P < 0.05). Herbage mass tended (P < 0.10) to be lower when heavy stocking rates were used in all years, but was not affected (P > 0.05) by grazing system. Significant relationships (P < 0.001) among IVDOM, ADF and NDF were found. Neither grazing system nor stocking rate appeared to affect the quality of herbage ingested by cattle grazing alfalfa-grass pastures. Key words: Alfalfa, pasture, grazing system, stocking rate

The effects of sward characteristics and supplement type on the herbage intake and milk production of summer‐calving cows

AbstractHigh (H; 27 350 m−1:) or low (L. 13 300 m‐1) tiller density perennial ryegrass swards were created in the mid‐ and late grazing season by imposing different sward heights in the spring. Summer‐calving cows then grazed these swards from 6 June to 2 September 1992 and were offered 5 kg fresh weight hd−1 d−1 of either a barley (S) or a molassed sugar beet pulp (F) based supplement. The factorial combination of sward and supplement types resulted in four experimental swards being grazed by thirteen Holstein/Friesian cows each.Supplement F contained more crude fibre (110 vs. 58 g kg−1) and less metabolizable energy [12–5 vs. 13–2 MJ kg−1 dry matter (DM)] than supplement S. Herbage on the H sward contained more metabolizable energy (11–9 vs. 104 MJ kg−1 DM) and crude protein (232 vs. 205 g kg−1 DM), had fewer rejected areas f 16–5 vs. 26–9%) and a higher live‐dead tiller ratio (4–6 vs. 2–1) than that on the L sward.Sward, but not supplement type, significantly affected the intake of grazed herbage (P<0–001). On average, the herbage intakes of cows grazing II swards were higher than for L swards (14–5 vs. 11 6kg DM d−1) and those of cows on the S and F supplements were 12–6 and 13–5 kg DM d−1 respectively. Averaged over the grazing period, sward and supplement had no significant effects on milk yield, milk composition or yield of constituents. When expressed on an average weekly basis, cows grazing an L sward and offered the F supplement on occasions had significantly lower milk yields and higher milk fat contents (P<005) than those grazing an H sward and offered the S supplement. There were no significant effects on cow live weight or condition score change. The results suggested that grazing swards with a high density of live tillers increased herbage intakes and on occasions milk yield, relative to low density swards. However, small increases in energy intake from sward and supplement effects were used primarily to ameliorate liveweight loss.

Short‐term ingestive behaviour of sheep and goats grazing grasses and legumes

Components of short‐term ingestive behaviour (bite weight, rate, depth, area, and volume) were recorded for six sheep and six goats grazing five grasses and four legumes each at two stages of growth (vegetative and reproductive). Animals were individually confined in metabolism crates and were offered prepared turves (41 × 27 cm) extracted from small monoculture field plots. Correlation relationships between sets of sward and ingestive behaviour variables were assessed using canonical analysis to evaluate the relative importance of individual variables within their own set in contributing to the sward effects (sward set) on ingestive behaviour, or to the animal responses (behaviour set) to sward variation. Overall, sward characteristics had a strong impact upon ingestive behaviour (canonical correlation = 0.95). In general, sward height had a greater effect (absolute value of standardised coefficient: AVSC = 1.184) on ingestive behaviour than did other sward characteristics (AVSC = 0.001–0.212), ...

Grazing Bites per Day of Goats on Some Tropical Grass Pastures and the Influence of Sward Characteristics

Grazing Bites per Day of Goats on Some Tropical Grass Pastures and the Influence of Sward Characteristics

The effects of stocking rate in spring, and topping on sward characteristics and dairy cow performance in a poor grass growing season

AbstractA comparison was made under continuous grazing between applying a high stocking rate in spring (H) to maintain the sward surface height (SSH) of a perennial ryegrass pasture at 5–6 cm and a low stocking rate (L) to maintain SSH at 10–12cm with mechanical topping in mid‐June. The experiment was carried out in the dry season of 1989 and a lack of rainfall markedly affected the treatments and consequently animals were offered supplementary concentrate and forage in July to compensate for reduced grass intake and low SSHs.Treatment H maintained the density of live grass tillers and live: dead tiller ratio in mid‐and late season, compared with the L treatment. The measured interval between defoliation of individual grass tillers was significantly less in the L pasture in samplings taken between 2 May and 29 August. January/February calving cows on the L pasture produced significantly more milk cow−1 with higher concentrations of protein and lactose, but less milk ha−1 compared with cows on the H sward. The results indicate that topping of a laxly grazed sward in drought conditions has no positive effects on sward characteristics or milk production.

Endophyte‐Free Tall Fescue Cultivars Grazed by Sheep: Forage Quality and Sward Characteristics

AbstractAlthough much work has focused on the performance of endophyteinfected (E+), Acremonium coenophialum Morgan‐Jones and Gams, tall fescue, Festuca arundinacea Schreb.; little information is available comparing performance attributes of endophyte‐free (E−) cultivars in the northeastern USA. Five paddocks of four cultivars [‘Festorina’, ‘Johnstone’, ‘Roa’, and ‘Kentucky 31’ (KY 31)] of E− tall fescue were rotationally stocked with ewes (Ovis aries) for 2 yr. Tall fescue and weed dry matter (DM) mass, leaf‐to‐stem ratio, and tiller density were determined both pre‐and post‐grazing and sward height was measured pro‐grazing. Forage crude protein (CP), acid‐detergent fiber (ADF), neutral‐detergent fiber (NDF), and in vitro dry matter disappearance (IVDMD) were determined by near infrared reflectance spectroscopy (NIRS). Total dry mass was higher for Festorina and KY 31 than for the other cultivars. Leaf‐to‐stem ratios were similar among cultivars. Forage height was greatest for Festorina and least for Johnstone. Fescue proportion of herbage biomass was greater and weed biomass lower for Festorina and KY 31 than for Roa and Johnstone. Tall fescue proportion of herbage biomass at the end of the trial was lowest for Johnstone. Mean tiller densities were similar for all cultivars and ranged from 2060 m−2 in spring to 1260 m−2 under stockpiling in fall. Pre‐grazed herbage CP of 204 g kg−1 was similar among cultivars. Roa tended to be low and Festorina high in both ADF and NDF, and IVDMD of Johnstone was higher than Festorina. Across seasons and years, ewe liveweight gain was higher for Johnstone than for the remaining cultivars, which were similar. Gains for Group 2 (late‐weaned) lambs were lower for KY 31 and were similar for the remaining cultivars. In light of this information, cultivar as well as endophyte status should be considered in designing experiments or planning grazing systems with tall fescue.

The influence of different types of grassland field margin on carabid beetle (Coleoptera, Carabidae) communities

A study of the impact of various field margin and field attributes on carabid beetle communities was implemented at IGER (North Wyke). Carabid beetles were caught in pitfall traps placed 0.5 m from either a hedge or a post and wire fence in 16 grassland field margins. The data were collected over the season April-mid November 1990. The relationship of the beetle assemblages to measurements of species numbers of field margin flora, sward husbandry, sward characteristics and physical attributes of the field margin itself was investigated. Contrary to expectations most species caught did not seem to be correlated to any measured variable. The majority of species trapped were present in both the hedge and fence field margins. However, a notable percentage (29.4) were present exclusively in the hedge margins, for example, Leistus fulvibarbis and Trechus obtusus. When the data were analysed by detrended correspondence analysis the margins were separated according to the soil moisture content and number of plant species in the margin; grazing regime and age of the pasture they surrounded.

Intake and behaviour responses by sheep to changes in sward characteristics under rotational grazing

AbstractA 10‐week grazing experiment was conducted on a perennial ryegrass sward with lactating ewes and their twin lambs. Three paddocks were rotationally grazed with rest periods of from 4 to 5 weeks. Sward surface heights at the start of each grazing were 145, 259 and 250mni for treatments RG1, RG2 and RG3. A further four paddocks were maintained by continuous variable stocking (CS) at sward surface heights (SSHs) of about 30, 60, 90 and 120mm. Sward and animal measurements were made on the two different grazing managements as the RG swards were grazed down, giving measurements at similar sward heights for treatments RG and CS.There was less green leaf and the total herbage mass present under RG was less than on CS swards at the same sward heights, demonstrating the differences in structure between rotationally and continuously grazed swards.Regression analysis of animal factors on sward factors showed that grazing behaviour was more highly correlated with green leaf mass than SSH or any of the other sward measurements. On the RG swards, maximum intake per animal was reached at about 1500 kg green leaf mass ha−1. A SSH of 60mm allowed the CS ewes to achieve the highest intake rate, but at this height the ewes on treatments RG2 and RG3 were restricted to approximately half this rate. The results suggest that green leaf mass or leaf area index, rather than sward surface height, could be used as a rational basis to relate intake of herbage to sward state for swards changing rapidly in leaf to stem ratio.

A comparison of diploid and tetraploid perennial ryegrass and tetraploid ryegrass/white clover swards under continuous sheep stocking at controlled sward heights. 1. Sward characteristics

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

Sward characteristics and animal performance in a leader/follower grazing system with cows and sheep

The recommended post grazing stubble height for dairy cows in a rotational grazing system in spring is 8 to 10 cm. However, this height leads to much stem elongation and reduction in sward quality in mid and late season. Consequently, pastures require topping in June/July to maintain grass quality and reduce sward deterioration, particularly in rejected areas around dung pats. O'Riordan (1989) suggested that a leader/follower rotational grazing system with ewes following dairy cows could improve pasture utilisation and eliminate the need for topping. This was confirmed by Swift et al. (1991) who also demonstrated that grazing at one ewe with twin lambs per cow improved the utilisation of grass and allowed for acceptable ewe and lamb performance without apparently decreasing cow grazing days or milk output.The objective of this work was to examine the effects of leader/follower rotational grazing with dairy cows and lambed ewes on grass tillering in a cool, wet western environment.

FORAGE: a model of forage intake in beef cattle

A deterministic simulation model (FORAGE) has been developed as an interface between the plant and animal components of a general rangeland ecosystem model (SPUR). The model predicts forage intake and diet selection of grazing beef cattle by simulating the mechanistic components of grazing behavior. Bite size, rate of biting, rate of intake and grazing time are modified by changes in sward characteristics. Sensitivity analyses revealed that the model is sensitive to underestimation of critical parameters. The model suggests that, when forage availability is limited, intake is limited by rate of intake and grazing time.

Effects of sward height and bulk density on bite dimensions of cattle grazing homogeneous swards

AbstractEffects of sward height and density on the dimensions and weights of bites taken by cattle were examined. In one experiment, swards of dallisgrass lamina were constructed by hand in a factorial combination of four heights (80, 150, 180 and 300 mm) and three densities (c. 700, 1500 and 2700 g m−3). In the other, swards of lucerne were constructed in a factorial combination of three heights (70, 150 and 250 mm) and three densities (1500, 2800 and 5900 g m−3). Treatments were replicated on three steers of 750 kg average weight. The first six bites taken from the sward were monitored, and functional relationships between sward characteristics and bite dimensions derived. Results from both experiments were similar. Average bite area was not constant as often assumed, but decreased linearly with density and increased quadratically with height, with slope negatively affected by density and height. In tail swards, bite area reached a plateau of c. 170 cm2, determined by the sweep of the tongue. In contrast with the widely used model, bite depth increased linearly with height, with slope negatively affected by density. Response of bite dimensions was explained by the mechanics of the interaction between tongue and jaw movements, and sward structure. Bite weight varied less than bite dimensions, because of compensatory effects between bite area, bite depth and density. Animals obtained heavier bites in tall sparse swards than on short dense ones of equal mass/area. Even in homogeneous swards, both density and height are necessary to predict bite weight.

Sward and Steer Variables Affecting Feasibility of Electronic Intake Measurement of Grazers

Forage intake is perhaps the most critical parameter in understanding performance of ruminants on pasture. The Thermal Conductivity Cannula (TCC) is an animal-carried device that measures forage intake without disturbing normal grazing patterns by counting the number of boli swallowed over time. To evaluate its accuracy, studies of the effects of animal size, forage availability, quality, and species differences were conducted. In a grazing study, bolus weights of heavy (533 kg) and light (360 kg) esophageally fistulated steers were monitored on 2 different grazing systems [tall fescue (Festuca arundinacea Shreb) + red clover (Trifolium sp.) season-long vs. tall fescue + red clover in spring and fall and bit bluestem (Andropogon gerardi Vit; cv. Kaw) in summer]. Boli weight differences between steer weights indicated that TCC intake estimation will require calibration for steer weight or use of uniform steers. Boli weights of heavy steers varied (P < 0.05) within (9.0 to 19.4 g) and among (19.4 to 30.2 g) forage species. That did not occur with light steers (average = 6.25). Analysis of data on a metabolic weight basis indicated that size of the oral cavity and the 'critical mass' needed to stimulate swallowing may be a factor as well as weight. Sward characteristics and quality parameters were poorly correlated with bolus weight. An indoor study using 3 steer weights (heavy-546 kg, medium-486 kg, and light-220 kg) fed orchardgrass (100%), alfalfa (100%), and orchardgrass X alfalfa hay (50/50) indicated that heavier steers always produced heavier boli but that the weight differences between steers had to be greater than 86 kg to be significantly different. Light steers produced most consistent boli weights over all feeds.

Intake and behaviour responses by sheep to changes in sward characteristics under continuous stocking

AbstractPerennial ryegrass pastures were maintained at sward surface heights (SSH) of 30, 60, 90 and 120 mm by continuous variable stocking using lactating ewes and their twin lambs in spring and non‐lactating (dry) ewes in autumn.The effects of SSH on ingestive behaviour, herbage intake, animal performance and sward structure and production were measured in spring, and again in autumn, when an additional SSH of 20 mm was also established.In spring, differences in sward structure were quickly established with mean tiller numbers of 41 000, 30 000, 21 000 and 19 000 m−2 and leaf area indices (LAI) of 1·5, 2·2, 3·3 and 4·1 at SSH of 30 to 120, respectively. By autumn the mean tiller numbers had fallen to 26 000, 26 000, 23 000, 18 000 and 13 000 m−2 and LAI to 1·0, 1·1, 1·5. 2·0 and 1·5 for treatments 20 to 120.The mean stocking rates for the ewes in spring were 27, 20, 22, and 19 ewes ha−1 and growth rates of their lambs were 208, 275, 250 and 263 g d−1 for treatments 30 to 120. In autumn the stocking rates maintained for dry ewes were 22, 15, 9, 4 and 0 for treatments 20 to 120.In spring, both grazing times (GT) and prehension biting rate (BR) were negatively correlated with SSH, while bite mass (BM) was positively correlated with SSH. However, mean daily intakes of organic matter (OM), were reduced only for animals grazing the 30 mm sward.In autumn, intake rate was lower only for the animals grazing the 20mm sward and GT and BR were not significantly affected by SSH.Relationships between SSH and, components of ingestive behaviour and intake, are presented and the control mechanisms involved are discussed. The results showed that the optimum sward surface height for continuously stocked swards, grazed by sheep, Was between 30 mm and 60 mm.

Simulating the influence of stocking rate, sward height and density on steer productivity and grazing behavior

A simulation model was written to study how sward characteristics affect steer performance and the grazing behavior of steers. This model, called INTERFACE, simulates grazing behaviour as affected by both horizontal and vertical distribution of forage quality throughout simulated swards. Simulated steers grazed small, rectangular pastures containing a tall fescue monoculture. Horizontally, the pasture was divided into 12 equally-sized sites with the water and mineral source both located in one site. Steers randomly selected a site for grazing. Vertically, the sward was divided into five layers, each of which varied in quality, i.e. proportion of cell wall, nitrogen, minerals or lignin. Results of trial simulations indicated that steers spent more time grazing sites near the water source and progressively less as distance from the water source increased. Grazing time increased as the sward became shorter and more inferior in quality. Although this model simulates diet selection simply as a random process, grazing time comparisons with actual grazing data suggest that this assumption may be adequate. This model can be used to test hypotheses about grazing behavior as influenced by forage quality and sward height.

Moderation of ingestive behaviour of beef ca le by grazing-induced changes in lucerne swards+

Intensive grazing of pastures may cause drastic and rapid changes in swards which have major effects on ingestive behaviour and diet. Twelve adult Angus cows (Bos Taurus), mean live weight of 482±19 kg, were allowed to graze on swards of lucerne (Medicago sativa L.) that were not grazed (TO), or had been grazed previously for 1 h (T1), or 2 h (T2) in a balanced changeover design. Herbage dry ma er (DM) masses (>5 cm) were 2611, 1895 and 1441 kg ha−1; leaf fractions were 0-48, 0-29 and 0-14; and herbage DM allowances per animal were 10·6, 7·9 and 6·0 kg h−1 for TO, T1 and T2, respectively. During a 1 h measured grazing session that followed an overnight fast, cows ingested 2-93, 1·71 and 0·66 kg DM h−1 with herbage DM intakes per bite of 1·6, 0·9 and 0·4 g for T0, T1. and T2, respectively. Rates of biting did not respond to sward treatment and averaged 30 bites min−1. Intake of leaf DM was estimated at 98, 70 and 6% of total DM intake for the same treatment sequence. Utilization of herbage allowance was 0·29, 0·23 and 0·12, for TO, T1 and T2, respectively. Metabolzable energy (ME) intake per animal was 30, 17 and 5 MJ h−1 and ME intake per bite was 16, 9 and 3 KJ for TO, T1 and T2, respectively. Data show that grazing-induced differences in sward characteristics moderate both ingestive behaviour and diet.

The effects of a flexible grazing management strategy and leader/follower grazing on the milk production of grazing dairy cows and on sward characteristics

AbstractAn experiment was carried out during 1984 to examine the effects of three alternative grazing strategies for January/February calved British Friesian dairy eows on sward and animal production. Cows were rotationally grazed across 1 d paddocks without concentrate supplementation from 30 April to 1 October. A flexible grazing (EG) treatment involved manipulating residual herbage height, as assessed by a rising‐plate sward stick, with cows initially grazing to 80 mm, reducing to 60 mm when milk yield declined below 20 kg d−1 and finally to 50 mm when milk yield declined below 15 kgd−1. Control (C) cows grazed to a constant residual herbage height of 60 mm throughout the season (a 60‐inm rising‐plate sward stick height is equivalent to a sward surface height of approximately 80 mm). On a further treatment a leader/follower (LF) approach was used, with cows paired for calving date and parity and within pairs allocated to either a high‐(leader) or a low‐yielding (follower) group, according to milk yield at turnout, with the leader group grazing 1 d ahead of the follower group. Overall stocking rates on C and LE treatments were identical but herbage allowances differed as a result of treatment effects.Animal performance data for the FG, C and LE treatments, respectively, were: milk yield (kg d−1) 14·5, 14·7 and 16·0 (s.e. 0·59); milk fat yield (g d−1) 577, 571 and 637 (s.e. 29); milk protein yield (g d−1) 528, 527 and 576 (s.e. 19); and liveweight gain (kg d−1) 0·09, 0·20 and 0·14 (s.e. 0·04).Overall, there was no benefit in animal production following lax grazing in spring even with high‐yielding cows, and this approach resulted in the accumulation of stem and senescent material in the sward in mid‐season. However, preferential treatment of high‐yielding cows by grazing as a leader group in a leader‐follower system resulted in higher milk production, particularly in late season, with an overall improvement in milk yield for the LF treatment of 9% relative to treatment C.