Effect of different grazing management systems on the herbage mass and pasture height of a Nardus stricta grassland in western Scotland, United Kingdom

The aims of this study were to examine the effect of three grazing treatments (year‐round stocking rates of 0·8 ewes ha^?1, 0·5 ewes ha^?1 and 0·5 ewes ha^?1 plus grazing cattle in summer), imposed for 4 years, on the herbage mass and surface height of a Nardus stricta‐dominated grassland in western Scotland and to obtain estimates of annual productivity of this grassland. Nardus stricta‐dominated grassland comprised proportionately 0·20 of the grazing area. Stocking rate of sheep had no significant effect on the herbage mass of the grassland in the first 2 years of the experiment, although mean summer pasture heights were significantly higher under the lower stocking rate of sheep. The pasture on the treatment with cattle grazing in summer had a significantly lower herbage mass and lower surface height than the two sheep‐only grazing treatments. Year‐to‐year variation in the herbage mass and surface height of herbage in summer was greater than the effect of treatments. Despite changes in surface height, the structural diversity of the grasslands was not increased by the treatments. The annual production of vascular plant material ranged from 417 g DM m^?2 in 1994 to 628 g DM m^?2 in 1996.     

Defoliation patterns and their implications for the management of vegetative tropical pastures to control intake and diet quality by cattle

This study assessed the use of pasture attributes to control daily intake and diet quality during progressive defoliation on pastures of Axonopus catarinensis. Three consecutive 12‐day grazing treatments of progressive defoliation were conducted with Brahman cross‐steers. Daily forage intake and defoliation dynamics were assessed using a pasture‐based method. The treatments differed in initial sward height (33, 44 and 61 cm) and herbage mass (1030, 1740 and 2240 kg ha^?1). The post‐grazing residual sward height, at which forage intake decreased, appeared to increase with the initial sward height (12·3, 14·6 and 15·5 cm). Steers grazed up to four distinctive grazing strata in all treatments. The depth and herbage mass content of the top grazing stratum were at least five times higher than the lower grazing strata in all treatments. This explains why forage intake decreased when the top grazing stratum was removed in approximately 93% of the pasture area in all treatments, equivalent to approximately 7% of the pasture area remaining ungrazed. We conclude that the residual ungrazed area of the pasture, rather than residual sward height, can be used to develop grazing management strategies to control forage intake and diet quality in a wide range of pasture conditions.     

Impact of spatial heterogeneity of plant species on herbage productivity,herbage quality and ewe and lamb performance of continuously stocked,perennial ryegrass–white clover swards

The benefits of white clover (Trifolium repens L.) in pastures are widely recognized. However, white clover is perceived as being unreliable due to its typically low content and spatial and temporal variability in mixed (grass‐legume) pastures. One solution to increase the clover proportion and quality of herbage available to grazing animals may be to spatially separate clover from grass within the same field. In a field experiment, perennial ryegrass (Lolium perenne L.) and white clover were sown as a mixture and compared with alternating strips of ryegrass and clover (at 1·5 and 3 m widths), or in adjacent monocultures (strips of 18 m width within a 36‐m‐wide field). Pastures were stocked by ewes and lambs for three 10‐month grazing periods. Over the 3 years of the experiment, spatial separation of grass and clover, compared with a grass–clover mixture, increased clover herbage production, although its proportion in the sward declined through time (0·49–0·54 vs 0·34 in the mixture in the first year, 0·28–0·33 vs 0·15 in the second year and 0·03–0·18 vs 0·01 in the third year). Total herbage production in the growing season in the spatially separated treatments decreased from 11384 kg DM ha^?1 in the first year to 8150 kg DM ha^?1 in the third year. Crude protein concentration of clover and grass components in the 18‐m adjacent monoculture treatment was greater than the mixture treatment for both clover (310 vs 280 g kg^?1 DM) and grass (200 vs 180 g kg^?1 DM). There was no clear benefit in liveweight gain beyond the first year in response to spatially separating grass and clover into monocultures within the same field.     

Performance and environmental effects of forage production on sandy soils. I. Impact of defoliation system and nitrogen input on performance and N balance of grassland

Grassland and its management is central to the productivity of and nitrogen (N) losses from dairy farms in north‐west Europe. Botanical composition, production and N surplus of grassland were assessed during five consecutive years. The experiment consisted of all combinations of five defoliation systems: cutting‐only (CO), rotational grazing (GO), grazing + one (MSI) or two silage cuts (MSII) and simulated grazing (SG). Four mineral N fertilization rates (0–300 kg N ha^?1 year^?1) and two slurry levels (0 and 20 m³ slurry ha^?1 year^?1) were applied. Fertilizer N was more efficient in producing net energy (NEL) in grazing‐dominated, low white clover systems (GO and MSI systems: 70 and 88 MJ NEL kg^?1 N) than in white clover‐rich systems (MSII, CO and SG systems: ≤60 MJ NEL kg^?1 N). While sward productivity in system MSI was similar to that in system GO, system MSII benefited from increased N₂ fixation at low N rates. There were small differences in NEL concentrations of the herbage between defoliation systems. Crude protein concentration of the herbage increased with increasing N supply from fertilizer, excreta and N₂ fixation. N surpluses (?63 to +369 kg N ha^?1 year^?1) increased with increasing grazing intensity and increasing N fertilization rate. The average response in N surplus applied was 0·81, 0·59, 0·40, 0·33 and 0·24 kg N ha^?1 in systems GO, MSI, MSII, CO and SG respectively.     

The effect of initial spring grazing date and subsequent stocking rate on the grazing management, grass dry matter intake and milk production of dairy cows in summer

The objective of this study was to investigate the effects of an early (February; F) or delayed (April; A) primary spring grazing date and two stocking rates, high (H) and medium (M), on the grazing management, dry matter (DM) intake of grass herbage and milk production of spring‐calving dairy cows grazing a perennial ryegrass sward in the subsequent summer. Sixty‐four Holstein‐Friesian dairy cows (mean of 58 d in milk) were assigned to one of four grazing treatments (n = 16) which were imposed from 12 April to 3 July 2004. Cows on the early spring‐grazing treatment were grazed at 5·5 cows ha^?1 (treatment FH) and 4·5 cows ha^?1 (treatment FM) while cows on the late‐grazing treatment were grazed at 6·4 cows ha^?1 (treatment AH) and 5·5 cows ha^?1 (treatment AM). The organic matter digestibility and crude protein concentration of the grass herbage were higher on the early‐grazing treatment than on the late‐grazing treatment. The cows on the FM treatment had significantly (P < 0·001) higher milk (24·5 kg), solids‐corrected milk (22·5 kg), fat (P < 0·01, 918 g) and protein (831 g) yields than the other three treatments. Cows on the FM treatment had a higher (P < 0·001) DM intake of grass herbage by 2·3 kg DM per cow per day than cows on the AH treatment, which had a DM intake significantly lower than all other treatments (15·2 kg DM per cow per day). The results of the present study showed that grazing in early spring has a positive effect on herbage quality in subsequent grazing rotations. The study also concluded that early spring‐grazed swards stocked at a medium stocking rate (4·5 cows ha^?1; FM) resulted in the highest DM intake of grass herbage and milk production.     

Effects of date of autumn closing and timing of winter grazing on herbage production in winter and spring

Growth of grass herbage in Ireland is highly seasonal with little or no net growth from November to February. As a result, feed demand exceeds grass supply during late autumn, winter and early spring. At low stocking rates [≤2 livestock units (LU) ha^?1], there is potential to defer some of the herbage grown in autumn to support winter grazing. This study examined the effects of four autumn‐closing dates and four winter‐grazing dates in successive years on the accumulation of herbage mass and on tiller density in winter and subsequent herbage production at two sites in Ireland, one in the south and one in the north‐east. Closing swards from grazing in early and mid‐September (north‐east and south of Ireland respectively) provided swards with >2 t DM ha^?1 and a proportion of green leaf >0·65–0·70 of the herbage mass above 4 cm, with a crude protein (CP) concentration of >230 g kg^?1 DM and dry matter digestibility (DMD) of >0·700. The effects of autumn‐closing date and winter‐grazing date on herbage production in the subsequent year varied between the two sites. There was no significant effect of autumn‐closing date in the north‐eastern site whereas in the south earlier autumn closing reduced the herbage mass in late March by up to 0·34 t DM ha^?1 and delaying winter grazing reduced the herbage mass in late March by up to 0·85 t DM ha^?1. The effects of later grazing dates in winter on herbage mass continued into the summer at the southern site, reducing the herbage mass for the period from late March to July by up to 2 t DM ha^?1. The effects of imposing treatments in successive years did not follow a consistent pattern and year‐to‐year variation was most likely linked to meteorological conditions.     

Effect of maize grain and herbage allowance on estimated metabolizable energy intake and animal performance in beef cattle finishing systems

This study investigated the effects of levels of supplementation with maize grain and herbage allowance (HA) on grass herbage and maize intake, animal performance and grazing behaviour in two replicated grazing experiments with Angus beef cattle in Argentina. In Experiment 1, the response to increasing HA (2·5, 5·0 and 7·5 kg DM herbage 100 kg^?1 live weight (LW) d^?1 with and without 0·5 kg DM maize grain 100 kg^?1 LW d^?1) was investigated. In Experiment 2, the responses to level of maize grain offered (0, 0·5 and 1·0 kg DM maize grain 100 kg^?1 LW d^?1) at an HA of 2·5 kg DM herbage 100 kg^?1 LW d^?1 and an HA of 5·0 kg 100 kg^?1 LW d^?1 without maize grain were assessed. In Experiment 2, soyabean meal was added to control the crude protein concentration in the diet. Two methods were used for intake estimations: pre‐ and post‐feeding herbage mass difference, and the use of the n‐alkane and ¹³C technique. The latter predicted most accurately the metabolizable energy requirements calculated from live weights and liveweight gain of beef cattle attained in each treatment in both experiments. Increasing HA significantly increased herbage intake and liveweight gain (P < 0·01), and general quadratic relationships between these variables could be fitted across experiments despite differences in animal and pasture characteristics. Increasing the amount of maize grain offered significantly reduced herbage intake and grazing time, but increased liveweight gain and digestibility of the diet. Substitution rate increased with increasing HA in Experiment 1 but was not affected by level of maize supplementation in Experiment 2. These relationships will aid the development of grazing management models for Argentinean conditions.     

The long-term effects of a range of pasture treatments applied to three semi-natural hill grassland communities.

Five pasture treatments were applied to three semi-natural hill grassland communities. The pasture treatments were: (1) controlled grazing, (2) controlled grazing + lime, (3) controlled grazing + lime + phosphate, (4) controlled grazing + lime + phosphate + oversown white clover and (5) controlled grazing + lime + phosphate + oversown white clover + oversown perennial ryegrass. The communities were dominated by Agrostis/Festuca (site 1), Molinia (site 2) and Nardus (site 3). The Nardus at site 3 was substantially reduced by herbicide before treatments were applied. All treatments were grazed simultaneously by mature wether sheep on three occasions each year to a residual herbage mass of 560 kg DM ha^?1. There were two grazing periods, each of 4 weeks duration, beginning in mid-May and mid-July respectively and a further grazing period of 3 weeks duration beginning in mid-October. The number of sheep grazing days and liveweight gain of sheep were recorded during each grazing period for 13 years at each site. Organic matter intake (OMI) and digestibility (OMD) of ingested herbage were measured in years 2, 5 and 13. Mean daily OMI per head ranged from 1290 g for treatment 1 to over 1400 g for treatments 4 and 5. OMI values were higher for the Agrostis/Festuca site (mean OMI 1450 g) than for the Molinia and Nardus sites (1310 g and 1370 g respectively) largely owing to differences in the values for treatments 1, 2 and 3. OMI values for each treatment decreased by around 300 g between May and October. Mean OMD values from treatments 1, 2 and 3 were higher for the Agrostis/Festuca site (0·66) than for the Molinia and Nardus sites (0·63 and 0·64 respectively). The OMD values for treatments 1, 2 and 3 at the Molinia and Nardus sites declined by between 0·05 and 0·02 between years 2 and 13 and also showed the greatest decrease between May and October (0·08). OMD values for treatments 4 and 5 (0·67 and 0·69 respectively) were higher than for treatments 1, 2 and 3 at all sites and levels were maintained over 13 years. Individual liveweight gains of sheep increased from treatment 1 (?18 g d^?1) to treatment 5 (82 g d^?1), but they decreased over time on all treatments. The Agrostis/Festuca site gave 17% more annual sheep grazing days than the Molinia site and 33% more than the Nardus site. The mean number of annual sheep grazing days for each treatment ranged from 2250 for treatment 1 to 3640 for treatment 5. Annual sheep grazing days increased over 13 years by between 35 and 45% for treatment 1 and 55 and 70% for treatment 5. The results are described in relation to the changes in pasture composition and herbage accumulation.     

Cattle and sheep grazing effects on soil organisms, fertility and compaction in a smooth-stalked meadowgrass-dominant white clover sward

This experiment was carried out to improve understanding of sward and soil responses to cattle and/or sheep rotational grazing of low-input (no N fertilizer), natural swards dominated by smooth-stalked meadowgrass (Poa pratensis) syn. Kentucky bluegrass and based on white clover (Trifolium repens). Treatments during two grazing seasons (1989–90) were: cattle grazing alone (C); cattle grazing followed by topping (CT); cattle grazing followed by sheep grazing (CS); and sheep grazing alone (S), Mean target pre- and post-grazing herbage masses were 2200 and 1100 kg dry matter (DM) ha^?1. Plants in sheep-grazed swards regrew more quickly and accumulated more herbage (8·28 compared to 5·35 t DM ha^?1 for cattle-grazed swards, unadjusted for rejected area) than in other treatments. After 2 years, soil in sheep-grazed areas contained 0·25% N, 5·7 kg available P ha^?1, and 379 kg K ha^?1, compared to an average of 0·19, 3·9, and 179 respectively for the same soil nutrients in cattle-grazed treatments. Besides differences in manure distribution and sward rejection, differences in soil compaction among treatments also may have affected soil organisms and thus plant growth. After 2 years, soil bulk densities (g cc^?1) were 1·37, 1·37, 1·27, and 1·12; soil penetrometer measurements (kg cm sec^?1 sec^?1) to 20-cm soil depth were 9·8, 9·3, 9·5, and 6·7; soil nematodes per 100 g of soil were: 5333, 8705, 2810, and 15208; soil rotifers per 100 g soil were: 288, 242, 715, and 33; and earthworms m^?2 (and their biomass (g m^?2)) were 262 (205), 157 (162), 344 (409), and 294 (343) for C, CT, CS, and S treatments, respectively.     

Open pasture,silvopasture and sward herbage maturity effects on nutritive value and fermentation characteristics of cool‐season pasture

In Appalachian USA, silvopasture offers promise of increased farm productivity. A synchronized, temporal understanding of open pasture (OP) and silvopasture (SP) nutritive characteristics is essential for grazing system development. We examined pasture‐type nutritive‐value relationships when herbage was harvested based on morphological maturity rather than calendar date. Neutral detergent fibre and acid detergent fibre (ADF and NDF) content were greater in silvopasture, while organic matter (OM) was lower (P < 0·05). Digestibility of SP herbage dry matter (DM) and OM tended (P = 0·10) to be lower (418 vs. 471 and 437 vs. 491 g kg^?1 respectively). Neutral detergent fibre digestibility was greater (P < 0·05) for OP than SP forage (538 vs. 480 g kg^?1), and ADF tended to be greater (P = 0·10; 551 vs. 501). Open‐pasture forage fermentation effluent exhibited slightly higher microbial richness and Shannon diversity than SP. However, overall community composition of both bacteria and archaea did not differ between pasture types or sampling times. Pasture types show proximate analyses differences generally favourable to OP, although both have similar overall nutritive value. In addition, the SP sward exhibited a 4‐ to 6‐days delay in reaching equivalent maturity. Conversion of farm woodlots to SP would increase overall herbage production and improve pasture management flexibility.     

Bio‐economic efficiency of creep supplementation of forage legumes or concentrate in pasture‐based lamb production system

A 2‐year study in the Central Anatolian Region of Turkey compared the performance of pasture‐fed suckling lambs and their dams, set‐stocked on grass‐legume pastures supplemented either with forage legumes or concentrate through a creep grazing/feeding system in a randomized block design. The treatments included continuous pasture grazing + creep grazing alfalfa; continuous pasture grazing + creep grazing birdsfoot trefoil; continuous pasture grazing + creep feeding concentrate (170 g kg^?1 CP; 11.3 ME MJ kg^?1 DM); and continuous grazing without creep feeding (control). In both years, creep feeding/grazing commenced in early June following a 42‐day pasture grazing period (period 1) and continued until mid‐summer for two separate periods of 21 days each (periods 2 and 3). Creep‐supplemented lambs grew faster (p < .001) than those that grazed pasture alone, with no significant difference across all creep supplementation treatments. Across the years, the lambs grew at 223 and 161 g per head day^?1 for creep‐supplemented and control groups respectively. None of the lamb feeding strategies affected the ewe liveweight gains (p > .05). Results from a bio‐economic optimization model, however, showed that supplementing the pasture with birdsfoot trefoil and alfalfa in periods 2 and 3, respectively, maximized economic returns with an extra profit of US$88.83 per lamb above those that grazed the pasture alone.     

Liveweight gains of lambs from Caucasian clover/ryegrass and white clover/ryegrass swards on soils of high and low fertility

The high nutritive value and persistence under a wide range of climatic and soil fertility conditions make Caucasian clover a potentially useful forage legume but there is little information about the performance of livestock grazing Caucasian clover/grass swards. This study compared liveweight gains of lambs grazing Caucasian clover/perennial ryegrass and white clover/perennial ryegrass swards on high fertility (Olsen P 20 mg L^?1, SO₄‐S 12 mg kg^?1) and low fertility (Olsen P 11 mg L^?1, SO₄‐S 7 mg kg^?1) soils from 1998 to 2001 in the South Island of New Zealand. Mean annual liveweight gains were 1178 kg ha^?1 for Caucasian clover/perennial ryegrass and 1069 kg ha^?1 for white clover/perennial ryegrass swards at high fertility compared with 1094 kg ha^?1 and 1015 kg ha^?1, respectively, at low fertility. There was a higher mean proportion of clover in Caucasian clover/perennial ryegrass (0·19) than white clover/perennial ryegrass (0·11) swards, but there were no differences in total herbage production between the two clover/perennial ryegrass swards. The mean concentration of crude protein in the herbage of Caucasian clover (302 g kg DM^?1) was higher than that in white clover (287 g kg DM^?1) and grass herbage (227 g kg DM^?1). Estimated mean metabolizable energy concentrations in the herbage were 12·5 MJ kg DM^?1 for the two clovers and 11·6 MJ kg DM^?1 for grass herbage. The difference in liveweight gain between swards on soils of high and low fertility was associated with an increase in total herbage production of similar composition and nutritive value, giving a greater number of grazing days for the swards on soils of high than low fertility.     

The long-term effects of a range of pasture treatments applied to three semi-natural hill grassland communities. 1. Pasture production and botanical composition

Five pasture treatments: (1) controlled grazing, (2) controlled grazing + lime, (3) controlled grazing + lime + phosphate, (4) controlled grazing + lime + phosphate + oversown white clover and (5) controlled grazing + lime + phosphate + oversown white clover + oversown perennial ryegrass were applied to three semi-natural hill grassland communities. The communities were those dominated by Agrostis/Festuca, Molinia and Nardus. The proportion of Nardus at the Nardus-dominant site was substantially reduced by herbicide before treatments were applied. All treatments were grazed simultaneously by mature wether sheep on three occasions each year. There were two grazing periods each of 4 weeks duration between mid-May and mid-August with a further grazing period of 3 weeks starting mid-October. During each grazing period stock numbers were set so that a residual herbage mass of 560 kg DM ha ^?1 remained at the end of the grazing period. Measurements of net herbage accumulation (NHA) were made annually over a period of 13 years at each site. The green:dead ratio of grasses, species composition of the pasture and the pH of the soil were measured at intervals during the experiment. Estimates of mean annual NHA ranged from 3860 kg DM ha^?1 for treatment 1 (controlled grazing) to 5170 kg DM ha^?1 for treatment 5 (oversown white clover and perennial ryegrass). The application of lime and phosphate increased annual NHA by 300–350 kg DM ha^?1 with a further increase of around 400 kg DM ha^?1 when white clover was sown. Increases in NHA between year 1 and year 13 ranged from 30% for treatment 1 to around 55% for treatment 5. Although there was no difference in the mean NHA between sites, the herbage from the Agrostis/Festuca site contained a higher proportion of green grass and white clover than that from the other sites. The highest levels of green grass and white clover were found on the oversown treatments at each site. The grazing pressure exerted produced relatively little change in the botanical composition at the Agrostis/Festuca site. At the Molinia-dominant site the Molinia was largely replaced by Nardus during the first 6 years and Nardus also increased in cover at the Nardus site. Application of lime and phosphate generally increased the proportion of Poa pratensis, Festuca rubra and Agrotis tenuis but did not halt the spread of Nardus at the Molinia and Nardus sites. White clover and perennial ryegrass were successfully introduced by oversowing and proportions remained high throughout the 13 years. The cover by bryophyte spp. increased at all sites with the greatest increases occurring in each case on the less comprehensive pasture treatments. These results suggest that on Agrostis/Festuca-dominant pastures herbage biomass production can be increased with relatively low-cost pasture treatments while maintaining Species diversity. However, Nardus and Molinia dominant pastures are likely to require more comprehensive pasture treatments involving sown grasses and white clover to provide herbage of acceptable quality and avoid an increase in Nardus and bryophytes in the sward. With a regime of episodic summer grazing and the addition of fertilizers oversown pastures can be maintained over long periods of time.     

Impact of deferred grazing and fertilizer on herbage production,soil seed reserve and nutritive value of native pastures in steep hill country of southern Australia

Developing sustainable grazing management systems based on perennial species is critical to preventing land degradation in marginal land classes. A field study was conducted from 2002 to 2006 to identify the impacts of deferred grazing (no defoliation of pastures for a period generally from spring to autumn) and fertilizer application on herbage accumulation, soil seed reserve and nutritive value in a hill pasture in western Victoria, Australia. Three deferred grazing strategies were used: short‐term deferred grazing (no defoliation between October and January), long‐term deferred grazing (no defoliation from October to the autumn break) and optimized deferred grazing (withholding time from grazing commenced between annual grass stem elongation and seed head emergence and concluded in February/March). These treatments were applied with two fertilizer levels (with or without fertilizer at 50 kg phosphorus ha^?1 and 2000 kg lime ha^?1 applied in year 1 only) in a factorial arrangement and two additional treatments: continuous grazing (CG) and no grazing (NG) in year 1. The deferred grazing treatments on average produced herbage dry matter of 4773 kg ha^?1, the NG produced 4583 kg ha^?1 and the CG produced 3183 kg ha^?1 in year 4 (2005–06) of the experiment. Deferred grazing treatments with and without fertilizer application produced an average of 5135 and 4411 kg DM ha^?1 respectively. Averaged over 4 years, deferred grazing increased the germinable seed pool of perennial grasses by 200% and annual grasses by 50% (except optimized deferred grazing that considerably decreased the annual grass seed pool) compared with the CG. The best of the deferred grazing strategies increased the digestibility of pastures by 7% compared with the CG. The results demonstrated that deferred grazing from spring to autumn followed by rotational grazing could be an effective tool to increase herbage production and soil seed pool and improve the digestibility of native pastures in the steep hill country of southern Australia.     

Bahiagrass (Paspalum notatum Flugge) management combining nitrogen fertilizer rate and defoliation frequency to enhance forage production efficiency

Bahiagrass (Paspalum notatum Flugge) pastures are widespread in warm climates worldwide and respond to nitrogen (N) fertilizer. Nitrogen fertilization has recently decreased because of increased cost and concerns regarding excessive N in the environment. Responses of bahiagrass to treatments representing three alternative levels of pasture management were assessed. Treatments, each including 56 kg N ha^?1 applied for each growth period, were as follows: (i) six harvests with a total of 336 kg N ha^?1 annually (referred to as intensive management), (ii) three harvests with 168 kg N ha^?1 annually (intermediate management) and (iii) two harvests with 112 kg N ha^?1 annually (extensive management). The intensive management produced the most forage with the highest nutritive value. Intermediate management, with only half the amount of N fertilizer, produced at least 80% of the forage yield each year as the intensive management treatment (4‐year average of 8236 vs. 9122 kg ha^?1 for the intermediate and intensive management treatments respectively) with forage of acceptable nutritive value for some classes of livestock. Limited forage production from the last harvest each year restricts autumn management opportunities, even though crude protein concentration was usually sufficient for some classes of livestock. Extended growth periods, as those that occur with the less‐intensive management treatments, provide opportunities to accumulate forage for late‐season grazing. Matching livestock enterprises to the forage produced, particularly in terms of nutritive value, can contribute to favourable livestock production responses from a range of bahiagrass pasture management approaches.     

The effects of poloxalene on ingestion by cattle grazing Lucerne†

The mechanisms that terminate meals of cattle grazing lucerne (Medicago sativa L.) are not well defined. Sub-acute bloat may lead to cessation of grazing and, consequently, surface active substances used in the treatment and prevention of bloat, such as poloxalene, may extend grazing meals and increase herbage intake. Twelve mature Angus cows (Bos taurus) were offered 0, 12·5 and 25·0 g poloxalene in 0·5 kg of crushed maize (Zea mays L.) kernels each day, immediately before two consecutive 1-h measured parts of a grazing meal on 21- to 24-day-old lucerne swards with a herbage dry matter (DM) mass (> 5 cm) of 2·03 t ha^?1 and herbage DM mass allowance of 3·55 kg hd^?1h^?1. Total herbage DM intake was 2·52 kg hd^?1 during the first hour and 1·54 kg hd^?1 during the second hour of the 2-h grazing meal. Differences in herbage intake were attributable to a cessation of grazing. Mean rates of biting were 26·3 and 14·8 bites min^?1 and mean DM intakes per bite were 1·82 and 4·38 g during the first and second part of meals, respectively. Poloxalene treatments caused a small linear decline in grazing time during the first part of meals and a larger increase in grazing time during the second part of meals. Lower rates of DM intake caused by poloxalene were offset by increases in grazing time. It was concluded that poloxalene moderated ingestive behaviour within grazing meals of immature lucerne and this response may have been at least partly due to the relief of sub-acute bloat.     

An evaluation of potassium and nitrogen fertilization of grassland, and date of harvest, on fermentation, effluent production, dry-matter recovery and predicted feeding value of silage

The effects of levels of application of potassium (K) fertilizer, and its interactions with both nitrogen (N) fertilizer and the growth interval between fertilizer application and harvesting on ryegrass herbage yield and chemical composition, and the fermentation, predicted feeding value, effluent production and dry-matter (DM) recovery of silage were evaluated in a randomized block design experiment. Twenty plots in each of four replicate blocks received either 0, 60, 120, 180 or 240 kg K ha^?1, each at either 120 or 168 kg N ha^?1. Herbage from the plots was harvested on either 24 May or 8 June and ensiled (6 kg) unwilted, without additive treatment, in laboratory silos. Immediately after harvesting, all plots received 95 kg N ha^?1 and were harvested again after a 49-day regrowth interval. From the primary growth, herbage DM yields were 6·31, 6·57, 6·74, 6·93 and 6·93 (s.e. 0·091) t ha^?1, herbage K concentrations were 15·5, 16·2, 19·1, 22·4 and 26·1 (s.e. 1·06) g kg^?1 DM and herbage ash concentrations were 57, 63, 71, 73 and 76 (s.e. 0·9) g kg^?1 DM, and for the primary regrowth herbage DM yields were 2·56, 2·73, 2·83, 2·94 and 2·99 (s.e. 0·056) t ha^?1 for the 0, 60, 120, 180 and 240 g K ha^?1 treatments respectively. Otherwise, the level of K fertilizer did not alter the chemical composition of the herbage at ensiling. After a 120-day fermentation period the silos were opened and sampled. The level of K fertilization had little effect on silage fermentation and had no effect on estimated intake potential, in vitro DM digestibility (DMD), DM recovery or effluent production. Increasing N fertilizer application increased silage buffering capacity (P < 0·05) and the concentrations of crude protein (P < 0·001), ammonia N (P < 0·01) and effluent volume (P < 0·01), and decreased ethanol concentration (P < 0·05) and intake potential (P < 0·05). Except for the concentrations of lactate and butyrate, delaying the harvesting date deleteriously changed the chemical composition (P < 0·001) and decreased intake potential (P < 0·001) and DMD (P < 0·001) of the silages. It is concluded that, other than for K and ash concentration, increasing the level of K fertilizer application did not alter the chemical composition of herbage from the primary growth or the resultant silage. Also, the level of K fertilizer application did not affect predicted feeding value, DM recovery or effluent production. Herbage yield increased linearly with increased fertilizer K application. Except for acetate and ethanol concentrations, there were no level of K fertilizer application by level of N fertilizer application interactions or level of K fertilizer application by harvest date interactions on silage fermentation or predicted feeding value. Increasing N fertilizer application from 120 to 168 kg ha^?1 had a more deleterious effect on silage composition and feeding value than increasing K fertilizer application from 0 to 240 kg ha^?1. Delaying harvesting was the most important factor affecting herbage yield and composition, and silage composition and had the most deleterious effect on silage feeding value.     

The effects of autumn closing date on sward leaf area index and herbage mass during the winter period

The provision of grass for early spring grazing in Ireland is critical for spring calving grass‐based milk production systems. This experiment investigated the effect of a range of autumn closing dates (CD), on herbage mass (kg DM ha^?1), leaf area index (LAI) and tiller density (m^?2) during winter and early spring. Thirty‐six grazing paddocks, closed from 23 September to 1 December 2007, were grouped to create five mean CD treatments – 29 September, 13 October, 27 October, 10 November, 24 November. Herbage mass, tiller density and LAI were measured every 3 weeks from 28 November 2007 to 20 February 2008; additionally, herbage mass was measured prior to initial spring grazing and tiller density was measured intermittently until September 2008. Delaying CD until November significantly (P < 0·05) reduced herbage mass (by approximately 500 kg DM ha^?1) and LAI (by approximately 0·86 units) in mid‐February. On average, 35% of herbage mass present on swards on 20 February was grown between 28 November and 30 January. LAI was positively correlated with herbage mass (R² = 0·78). Herbage mass increased by approximately 1000 kg DM ha^?1 as spring grazing was delayed from February to April. Tiller density increased from November to February, although it did fluctuate, and it was greatest in April (9930 m^?2). This experiment concludes that in the south of Ireland adequate herbage mass for grazing in early spring can be achieved by delaying closing to early mid‐October; swards required for grazing after mid‐March can be closed during November.     

Herbage intake and N excretion by sheep grazing monocultures or a mixture of grass and white clover

In 1988 and 1989, swards of grass (G0), while clover (C0) and grass/white clover (GC0) receiving no N fertilizer, and a grass sward supplied with 420 kg N ha^?1 (G420), were grazed by non-lactating sheep to maintain a sward surface height of 6 cm. Herbage organic matter (OM) intakes averaged between 1200 and 1700 g OM ewe^?1 d^?1. For treatments G0, C0, GC0 and G420 respectively, the ewes' live weight gain was 102, 112, 100 and 110 g d^?1 and changes in body condition scores were +0·28, +0·52, +0·36 and +0·44 units season^?1. However, the effect of treatment was not significant for either variable. There were similar levels of output of faecal N ewe^?1 but significantly more urinary N ewe^?1 was excreted on treatments C0 and G420, where the concentrations of N in herbage laminae were also higher. For example, in 1989, total daily N excreted was 39·7, 64·4, 44·0 and 63·3 g N ewe^?1 for G0, C0, GC0 and G420 respectively. Taking into account the mean daily stocking rates, which were 19·4, 26·6, 27·2 and 36·5 ewe ha^?1, the total faeces and urine returns over the season were 161, 358, 249 and 484 kg N ha^?1 for each treatment respectively. The herbage OM intakes ewes^?1 d^?1 measured in September and October were similar for C0 and G420, and so the intake of herbage OM ha^?1 d^?1 was related to stocking rate, i. e. the estimated herbage intake ha^?1 over the growing season for the white clover monoculture was 73% of that for N-fertilized grass. Excretal nitrogen returns to the pasture from grazed mono-cultures of clover were high, and similar to those from a grass sward receiving 420 kg fertilizer N ha^?1. Consequently potential losses of N to the environment are high under these management systems.     

Grazing intensity affects forage accumulation and persistence of Marandu palisadegrass in the Brazilian savannah

This 3‐year study evaluated the effects of grazing intensity on herbage and steer responses in continuously stocked Brachiaria brizantha cv. Marandu pasture in the Brazilian savanna. Treatments consisted of three grazing intensity levels, characterized by canopy heights of 15, 30 and 45 cm, measured twice per week. Responses variables included tiller population density (TPD), herbage accumulation rate (HAR) and body weight gain per area (WGA). A decline in TPD (1,237 vs. 767 tillers/m²) was observed from the first to the third grazing years, which influenced the HAR from the first to the third years (90.1 vs. 52.4 kg ha^?1 day^?1). A marked decline in body WGA (541 vs. 276 kg ha^?1 year^?1) was observed along the three years in pastures managed at a height of 15 cm, indicating that this is an unstable condition for Marandu palisadegrass pasture. HAR was similar for pastures managed at 30 or 45 cm and was relatively stable during the experimental period, averaging 91.8 and 99.1 kg ha^?1 day^?1 respectively. Body WGA was similar and constant throughout the experimental period for pastures managed at 30 (596 kg ha^?1 year^?1) and 45 cm (566 kg ha^?1 year^?1). Maintaining continuously stocked Marandu palisadegrass pastures at a 15 cm canopy height should be avoided due to long‐term decreases in plant persistence and animal body WGA, particularly when soil P is below critical levels at pasture establishment and during pasture utilization.