Grazing Events Research Articles

Assessing alternative grazing-tolerant algae for nursery culture of abalone, Haliotis iris

Feeding during the nursery stage of abalone aquaculture, from larval settlement to 10 mm in shell length (SL), is a major challenge in the intensification of abalone aquaculture. Commercial abalone nurseries typically settle larvae onto vertical plastic plates coated with algae that act as a settlement cue and an important post-settlement food source. It becomes increasingly difficult to maintain an adequate algal food supply as the abalones grow and for this purpose many nurseries use the alga, Ulvella lens, as it is a very effective settlement cue as well as offering a resilient food source for the developing abalones. However, juvenile abalones can deplete a film of diatoms on the plates before they are capable of ingesting U. lens, and once abalone reach ~ 5 mm SL the high grazing pressure may exceed even what U. lens can support, requiring nurseries to provide additional cultured algae or prematurely wean the juveniles onto manufactured diets. Three prospective microfilamentous algal species isolated from the tanks of a commercial abalone facility, were selected as potentially suitable nursery algae as they demonstrated resistance to intensive juvenile grazing pressure, displayed rapid vegetative growth, and could be triggered to mass sporulate as a means of rapidly coating nursery tanks. The current study involved two experiments and assessed the suitability of each species as a live algal feed for juvenile abalones compared to U. lens. These experiments measured: (1) ingestibility and grazing resistance of each alga against juvenile abalone 1–8 mm SL, and (2) the ability of each species to recover once grazers had been removed. Two algae (Ulvophyceae sp. 1 and 3) demonstrated the desirable properties of being easily grazed by abalones of a smaller size (average SL 2.33 mm and 2.20 mm respectively) than U. lens (2.89 mm) yet provide an algal film that is likely to be resilient and durable under grazing pressure. These algae also displayed significantly greater rates of recovery following grazing than U. lens (p < 0.01), an important attribute for restoring algal films in nursery systems between grazing events or between batches of juvenile abalones. The results of this study indicate that these novel algae have a combination of desirable characteristics for use in commercial abalone nurseries. Further experiments in commercial scale nursery systems should be pursued to assess the food value and performance of these species as a feed for juvenile abalones.

Temporal and spatial variability of structure dependent properties of a volcanic ash soil under pasture in southern Chile

Prairies are a main source for livestock feeding in southern Chile. The aim of this research was to define how grazing events and natural wetting and drying cycles (WD) affect the spatial and temporal variability of the soil?s structural properties. The investigation was conducted in a Duric Hapludand, Valdivia Series. Penetration resistance (PR) and volumetric water content (WC), measured in situ, were used to prepare maps which show i) temporal (1383 to 3047 kPa for 46 to 16% WC) and spatial changes, and ii) grazing events as an important factor influencing spatial changes in PR (differences of 3421 kPa between max and min values). Grazing and WD cycles induced changes in the soil?s mechanical stability and pore functions, which indicate that structure-dependent properties are dynamic. During the study, variations between 0.3 and 0.9 log im2 were detected for air permeability (ka), whereas air capacity (ACp) ranged between 5 and 18%. Soil mechanical strength also varied over time and showed changes in PR. The same instrument, however, cannot be used to identify changes in soil pore functions. Generally, after grazing events, soil deformation induced a reduction of air capacity and permeability; however, after WD cycles, soil pores were able to recover their functional integrity.

Nutritive value and physical characteristics of Xaraes palisadegrass as affected by grazing strategy

The aim of this study was to ascertain whether the defoliation frequency based on a fixed rest period would generate variable sward structural and physiological conditions at each subsequent grazing event. The relative importance of the physiological age was established in comparison with the chronological age in the determination of the forage nutritive value of Xaraes palisadegrass [Brachiaria brizantha (Hochst ex A. RICH.) STAPF. cv. Xaraes]. Two grazing frequencies were defined by light interception (LI) at initiation of grazing (95% LI – “target grazing” [TG] or 100% LI – “delayed grazing” [DG]) and one based on chronological time, grazing every 28 days (28-d). Forage produced under the TG schedule was mostly leaves (93%) with a higher concentration of crude protein (CP; 138 g/kg in the whole forage), a lower concentrations of neutral detergent fibre (NDF) in the stems (740 g/kg), and higher in vitro dry matter digestibility (IVDMD) of the leaves (690 g/kg), compared to the other treatments. Lower grazing frequency strategies (DG and 28-d) resulted in forage with higher proportions of stems (10 and 9%, respectively). Strategies based on light interception did not produce pre-graze forage with a uniform nutritive value, as the indicators varied across grazing cycles. The treatment based on fixed days of rest did not result in uniformity.

Grazing Intensity and Nitrogen Fertilization Affect Litter Responses in ‘Tifton 85’ Bermudagrass Pastures: I. Mass, Deposition Rate, and Chemical Composition

Plant litter deposition and composition affect nutrient cycling and sustainability of grazed grasslands, but the effect of management practices on litter responses has not been fully investigated. The objective of this study was to determine the effects of grazing intensity (postgraze stubble height, SH) and N fertilization on existing litter mass, litter deposition rate, and litter chemical composition in rotationally stocked ‘Tifton 85’ bermudagrass (Cynodon spp.) pastures. Three levels of SH (8, 16, 24 cm) were compared at the same interval between grazing events (28 d) and amount of N fertilization (250 kg N ha−1 yr−1). Three levels of N fertilization (50, 150, and 250 kg N ha−1 yr−1) were compared when SH (24 cm) and regrowth interval were constant (28 d). Existing litter mass (1730–2510 kg ha−1) and litter deposition rate (10–30 kg ha−1 d−1) increased as SH increased, but N fertilization had no effect on litter mass or deposition rate. Increasing SH from 8 to 24 cm resulted in lower existing litter N (20.5 vs. 19.2 g kg−1) and lignin (186 vs. 148 g kg−1) concentrations and a greater C/N ratio (24 vs. 26). Increasing N fertilization increased litter N concentration from 11.5 to 19.2 g kg−1 and decreased C/N ratio from 43 to 26, but N had no effect on lignin and acid detergent fiber (ADF) concentrations. Bermudagrass litter quantity was affected more by grazing intensity than by N fertilization, but N fertilization had a greater impact on litter composition than did grazing intensity.

Grazing Intensity and Nitrogen Fertilization Affect Litter Responses in ‘Tifton 85’ Bermudagrass Pastures: II. Decomposition and Nitrogen Mineralization

In many grassland ecosystems, nutrient cycling via plant litter is important for plant growth and persistence. Understanding dynamics of litter decomposition and nutrient release under different management practices is critical to understanding nutrient cycling in grasslands, but this topic has received relatively little attention in C4 grass pastures. The objective of this study was to determine the effects of grazing intensity (defined as postgraze stubble height, SH) and N fertilization on litter decomposition and N release in ‘Tifton 85’ bermudagrass (Cynodon spp.) pastures. Three levels of SH (8, 16, 24 cm) were compared at the same interval between grazing events (28 d) and amount of N fertilization (250 kg N ha−1 yr−1). Three levels of N fertilization (50, 150, and 250 kg N ha−1 yr−1) were compared when SH (24 cm) and regrowth interval were constant (28 d). Loss of litter mass was most rapid early in the decomposition period. Pasture SH had no effect on decomposition of litter mass, but increasing N fertilization increased decomposition rate. Immobilization of litter N began almost immediately after placement in the field regardless of treatment, did not reach its maximum for up to 60 d, and lasted more than 128 d for most treatments. Increasing SH and N fertilization increased N immobilization in plant litter. Nitrogen immobilization in bermudagrass litter occurs across a wide range of pasture management practices, impacting N availability for plant growth.

Validation of the Forage Brassica Calculator: A fertiliser forecasting system for forage brassica crops grown in New Zealand. Pasja and bulb turnips

Forage brassica calculators can be used to assist fertiliser consultants and farmers plan nitrogen (N) and phosphorus (P) applications for site-specific brassica production. The cost of each nutrient and the predicted productivity are used to recommend both economic and environmentally sound application rates. In this study, simulated yield was that modelled by PARJIB (a model that analyses and forecasts yield responses to nutrients) from the soil available nutrient levels, the potential yield and the fertiliser rates. The actual (observed) yields are those measured from the field. Simulations for ePasjaf (R2=0.96; root mean square of the deviation (RMSD) .3% (0.25 t/ha)) followed observed data closely with individual harvests at 60 and 90 days after sowing, consistent with observed data (R2&gt;0.93; RMSD.4% (0.20 t/ha)). The ePasjaf model is sufficiently robust to predict site specific N and P fertiliser requirements. However, the model may need to be extended to more than two grazing events. Simulations for bulb turnips (R2=0.10; RMSD.28.1% (2.70 t/ha)) was poor. Simulations predicted the same yield for different treatments within sites, while observed yields differed widely (4.12 t/ha). This was because experiments included establishment and seeding method treatments which are not currently accounted for by the calculators. Thus, practical use of the brassica calculators for assisting with fertiliser rates currently depends on other agronomic factors being managed optimally. Key words: agro-ecological, leachate, supplementary feed, water-holding capacity

Companion cropping chicory with winter forage cereals for grazing and forage conservation. Dry matter yields, nutritive characteristics and mineral content

Limitations to the current perennial ryegrass-based pasture system on dryland dairy farms in southern Australia has led to research into alternatives that can produce either additional DM, out of season feed or can improve nutritive characteristics. The use of winter annual crops followed by a summer crop have the potential to achieve these goals but often result in considerable periods where new crops are establishing and feed is not available for consumption. Companion cropping offers an option to overcome these limitations. The experiment reported in this paper examines the DM yields, nutritive characteristics and mineral content of companion cropping wheat or triticale at different sowing rates into an existing chicory monoculture over a 2-year period. We hypothesised that oversowing cereal crops in autumn into an existing stand of chicory would result in improvements in nutritive characteristics at ensiling, without adversely affecting DM yield or subsequent chicory DM yields following harvesting, thus negating the need to sow a new summer forage crop each year. Total DM yields for the chicory and cereal monocultures were similar over the experimental period, while DM yields for all triticale mixtures were higher than the chicory only treatment. Chicory produced lower DM yields for silage but higher DM yields at most grazing events. The crude protein and estimated metabolisable energy content of the chicory only treatment was higher than the cereal monocultures and all triticale/chicory mixtures at both silage harvests with wheat/chicory mixes being intermediate. The proportion of chicory in the mixed swards declined over the course of the experiment. The use of chicory with cereals resulted in no adverse effects on total DM yields, some improvements in nutritive characteristics and mineral content and a more continuous supply of DM compared with double cropping with annual species in winter and summer. This experiment has highlighted the potential of oversowing cereal forages into an existing chicory sward to contribute to DM production on dairy farms in southern Australia. Such forage mixes can provide flexibility into forage systems through the provision of forage for grazing in early winter, the production of high DM yield silage harvests and then subsequent feed supply over summer and early autumn.

The development of urchin barrens in seagrass meadows at Luscombe Bay, Western Australia from 1985 to 2004.

Herbivore grazing is a well-documented cause of habitat decline in terrestrial systems, but marine examples from seagrass meadows are rare. Here we present evidence that isolated urchin grazing events have caused further localized losses to seagrass meadows already degraded by eutrophication or other anthropogenic disturbances. By 1992 a substantial scar in Posidonia meadows at Luscombe Bay in Cockburn Sound, Western Australia, had been caused by grazing urchins. When seagrass transplants were placed at the site more than a decade later most were grazed and did not survive. GIS analyses on imagery from 1985 to 2004 indicated that rapid seagrass meadow decline coincided with the presence of an unusually large aggregation of the grazing urchin Heliocidaris erythrogramma. Evidence of some seagrass recovery after 1993 was also apparent after the manual removal of the urchins in late 1992. Restoration efforts in seagrass meadows should consider the potential for grazing damage, as is commonplace in terrestrial systems.

Nitrogen Losses under Different Cattle Grazing Frequencies and Intensities in a Volcanic Soil of Southern Chile

Chilean livestock production systems have intensified over the last years, with increasing amounts of N fertilizer inputs creating the potentiality for environmental damage through N pollution of water and air, so that alternative production strategies have been developed to reduce such environmental impacts. This study assesses N losses under different grazing frequencies and intensities on permanent pasture (Lolium perenne L., Festuca arundinacea Schreb., Dactylis glomerata L., and Trifolium repens L.) on an Andisol in Southern Chile. Four grazing strategies were evaluated: frequent-heavy (FH), frequent-light (FL), infrequent-heavy (IH), infrequent-light (IL), and a no grazing control (C) treatment, and each with three replicates in a randomized complete block design. Results of the experiment indicate that N leaching losses were greater in the FH treatment (58.7 kg available N ha -1 ; p < 0.05) and with most of the leaching occurring in spring (39%). On average, N ammonia (NH3) losses were 10% greater in the frequent grazing treatments in relation to the infrequent grazing treatments, since there were no significant differences (P ≤ 0.05) among individual grazing events for FH, FL and IH. Results indicate that grazing frequency affects leaching losses while grazing intensity affects ammonia emissions from the grassland. Grazing with dairy cows in Southern Chile should consider this environmental constraint to ensure sustainable production over time.

Light Absorption Components in Onondaga Lake, New York, U.S.A.

Features of light absorption are critical to optical aspects of water quality and in regulating the signal available in the emergent flux from the surface. Spectral characteristics, dynamics, and relationships with optically active constituents and common optical metrics, are documented for three light absorbing components in culturally eutrophic Onondaga Lake, New York, U.S.A., based on the results of a 5 year study. The absorption coefficient, a(m -1 ), is partitioned according to the additive components of colored dissolved organic matter (a CDOM ), non-algal particles (a NAP ), phytoplankton (a φ ), and water itself (a w ; known), based on laboratory measurements for near surface samples collected weekly for the spring to fall interval over the 2004-2008 period. Supporting bulk measurements included dissolved organic carbon, total suspended solids (TSS) and its organic and inorganic (FSS) fractions, the concentrations of total phosphorus and chlorophyll-a ([Chl]), downwelling irradiance profiles to determine the diffuse attenuation coefficient (K d ), the beam attenuation coefficient at 660 nm [c(660)], and Secchi disc depth. The average exponential slope values for a CDOM (0.0168 nm -1 ) and a NAP (0.0126 nm -1 ) were very similar to those reported for other case 2 systems. The shapes of a φ spectra, represented by the ratio a φ (440): a φ (676), were found to negatively depend on [Chl]. The largest component of a at 440 nm, the reference wavelength, in each of the 5 years was a CDOM (∼45 to 60 %), the smallest was a NAP (∼15 to 25 %). Progressive decreases in yearly average a φ , particularly over the last three years are documented in response to decreases in [Chl], driven by increased nutrient limitation and Daphnia grazing (2008 only). Wide short-term variations are demonstrated within years for the components of a, particularly in response to the timing of runoff and Daphnia grazing events. Strong positive relationships are reported between a NAP and both TSS and FSS, a φ (at both λ = 440 and 676 nm) and [Chl], and a p (a NAP plus a φ ) and both TSS and c(660). The summation of the absorbing components at 440 nm is demonstrated to be a strong predictor of K d . The utility of the information in supporting a model for K d and SD and advancing monitoring of water quality through measurements of surface reflectance is described.

Sources and processes of contaminant loss from an intensively grazed catchment inferred from patterns in discharge and concentration of thirteen analytes using high intensity sampling

Summary Contaminants in water from intensively grazed catchments have been shown to cause significant environmental impacts. Effective intervention to reduce contaminant loads depends on identifying their sources and processes of mobilisation and transport. In this study, flow (Q) and analyte concentrations (CA) from a 12 ha catchment in north-west Tasmania used for grazing dairy cattle were monitored at a fine temporal scale and used to infer sources and processes of loss. Three groups of analytes identified based on CA–Q relationships, which included hysteresis loops, demonstrated that the TP group (TP, DRP, TSS, TN, E. coli and Enterococcus) was transported by surface runoff processes while the behaviour of the NO3 group (NO3, TDS, Ca, Mg, Na) was explained by subsurface processes and pathways. The NH4 group (NH4, K) was dominated by the addition of large quantities of analyte from grazing. In addition to the CA–Q relationships, concentrations of most analytes decreased linearly over each season of runoff. NH4 and K concentrations decreased exponentially following grazing events while TP concentrations decreased linearly. The study demonstrated the importance of understanding surface water and groundwater interactions and that relationships between runoff events, analyte concentrations and management as revealed by a fine temporal sampling regime may yield significant insights to sources and processes of loss of analytes in surface flow, at a given scale.

The effect of dairy cows grazing in early spring on phosphorus loss in overland flows post first and second grazing events

The effect of dairy cows grazing in early spring on phosphorus loss in overland flows post first and second grazing events

Herbage Production, Nutritive Value and Grazing Preference of Diploid and Tetraploid Perennial Ryegrass Cultivars (Lolium perenne L.)

The objective of this study was to determine, under the soil and climatic conditions of Southern Chile, the effect of the ploidy of perennial ryegrass (Lolium perenne L.) cultivars on herbage production, nutritive value, grazing preference and utilization of pasture produced. This study was conducted in southern Chile, Valdivia Province, and was evaluated for 3 years. The tetraploid cultivars used were Quartet (4n), Gwendal (4n), Pastoral (4n) and Napoleon (4n). The diploid cultivars were Anita (2n), Jumbo (2n), Aries (2n), and Yatsyn 1 (2n). When the average sward height reached 20 cm, all plots were simultaneously grazed by dairy cows for a period of 24 h. Before and after grazing, sward height, dry matter availability and nutritive value were evaluated. Grazing preference was visually assessed every 5 min for a period of 2.5 h after the afternoon milking. During the 3-year period 20 grazing events were evaluated. A randomized complete block design, with eight cultivars and three replicates, was used. Diploid

Grazing strategies to protect soil physical properties and maximise pasture yield on a Southland dairy farm

intensive dairy cattle grazing on wet soil can have a detrimental effect on soil physical quality and consequently on pasture production. Soil physical properties (porosity, bulk density, saturated hydraulic conductivity) of a Pallic soil (Pukemutu silt loam) and pasture production were assessed on a dairy farm in Southland, New Zealand, under a number of different cattle grazing strategies: (i) normal grazing management on undrained land, (ii) normal grazing practice on drained land, (iii) restricted autumn grazing, (iv) restricted grazing when soil conditions were wet, (v) never pugged, and (vi) never grazed. a hand‐pushed cone penetrometer determined treatments (iv) and (v). Soil macroporos‐ity was significantly greater (P < 0.05) on the never grazed plot than all other treatments at post‐spring sampling each year. There were no significant differences in any soil physical properties measured on cattle grazed treatments. Spring pasture yield from the never grazed treatment was greater (P < 0.05) than the drained and undrained standard practice grazing treatments for one of the three seasons. The lack of treatment differences in soil physical properties and pasture yield from grazing treatments suggests that the never pugged grazing strategy failed to prevent soil compaction by dairy cows. To some extent this is expected as soil compaction occurs at soil water contents lower than the thresholds for pugging damage. However, the large number of grazing events when soil conditions were considered safe according to the never pugged treatment protocol, but when soil water content was greater than the plastic limit, probably contributed to both soil treading damage and compaction during the traditionally wet early spring period.

Reversing a tree regeneration crisis in an endangered ecoregion

Global food demand is growing rapidly. Livestock grazing can provide a valuable source of protein, but conventional grazing is often unsustainable. We studied an 800,000-ha section of a threatened ecoregion in southeastern Australia. Conventional management in the region involves continuous livestock grazing with few rest periods and regular fertilizer application. By using remotely sensed data on tree cover and extensive field data on livestock grazing regimes, soil chemistry, tree diameters, and tree regeneration, we show that the region is facing a tree regeneration crisis. Under conventional management, across the region, millions of hectares of land currently supporting tens of millions of trees will be treeless within decades from now. This would have severe negative ramifications for biodiversity and key ecosystem services, including water infiltration and shade provision for livestock. However, we identified an unexpected win-win solution for tree regeneration and commercial grazing. A relatively new practice in the region is fast-rotational grazing, characterized by prolonged rest periods in between short, intensive grazing events. The probability of regeneration under fast-rotational grazing was up to 4-fold higher than under conventional grazing, and it did not differ significantly from the probability of regeneration in ungrazed areas. In addition, trees were more likely to regenerate where soil nutrient levels were low. These findings suggest that the tree regeneration crisis can be reversed by applying low-input, fast-rotational grazing. New policy settings supporting these practices could signal a turning point for the region, from ecological decline to ecological recovery.

Degradation of sea urchin feces in a rocky subtidal ecosystem: implications for nutrient cycling and energy flow

During destructive grazing events in the Northwest Atlantic, sea urchins Strongylocen- trotus droebachiensis consume large amounts of kelp biomass, transforming this material into feces. To determine the role of urchin fecal material in nutrient cycling and energy flow in the shallow rocky subtidal zone, we monitored the physical, chemical, and microbial degradation of urchin feces at 6, 9, 12, and 16 m depth over 19 d at a wave-exposed site on the Atlantic coast of Nova Scotia by quan- tifying changes in fecal biochemical composition, pellet size, and settling velocity. We observed an exponential loss of fecal material and rapid degradation of total and labile organic matter fractions; this suggests that urchin fecal production plays an important role in local nutrient cycling and energy flow via the microbial food web. As the feces were further degraded there was a relative increase in organic carbon, nitrogen, lipid, and available energy content, and a decrease in the C:N ratio, sug- gesting that degraded urchin feces are an important food source for suspension- and deposit-feeding invertebrates. The settling velocity of the feces also decreased over time, likely due to a decrease in fecal pellet density. Older, less dense feces with a relatively high energy content are more likely to be suspended and transported horizontally, providing a mechanism for the export of kelp primary pro- duction to deeper, less productive waters.

Long-term dynamics of a semiarid grass steppe under stochastic climate and different grazing regimes: A simulation analysis

We built a grid-based spatial explicit stochastic model that simulates grazing events and basic processes like seedling establishment, growth or mortality of the dominant species in the grass steppes of Patagonia. After evaluating the model with field data, we performed simulation experiments aimed to explore the interaction of precipitation and grazing regimes on vegetation dynamics. Grazing generated a reduction in tussock density which results in a decline in aboveground net primary production (ANPP). Both response variables presented a non-linear behavior including high temporal variability and delay effects, which may prolong for decades. There was a clear threshold in the response of the variables to stock density, though changes become evident only when a highly selective grazing scenario was used. Under high stock density conditions, precipitation use efficiency (PUE) was 82% lower than the values for non-grazed runs. The inter-annual variability of precipitation was more important than the grazing regime in explaining differences in tussock density. Simulation results highlight important issues regarding rangeland management: grazing regime might be as important as stocking density as a degradation agent, temporal lags might obscure degradation processes for decades, the definition of monitoring variables need to consider their response time constants.

Migration of gastrointestinal nematode larvae from cattle faecal pats onto grazable herbage

This study investigated the effect of successive harvests of grazable herbage around cattle faecal pats on the population dynamics of infective gastrointestinal nematode larvae (L 3). Faecal material, collected from naturally infected calves, was deposited as pats during summer, autumn and winter on three different topographical aspects within a moist, temperate region of New Zealand. Herbage was harvested four times (22–248 days) from around the faecal pats to a height of 2 cm in three radial zones (0–20 cm, 20–35 cm and 35–45 cm from the centre of the faecal pat) and L 3 extracted. Harvest date was determined by herbage mass to simulate grazing events. L 3 extracted from herbage were predominantly Cooperia spp. More L 3 were recovered from faeces deposited in summer and autumn, than those deposited during winter. L 3 concentration on herbage was highest ( P < 0.001) in the zone nearest the pat for all except the fourth harvest. Mean concentrations of L 3 on herbage were 11,447, 3154, 337 and 102 L 3/kg dry matter herbage, for the four successive harvests, respectively. Microclimate differences as affected by aspect had a marked effect on herbage growth, but did not significantly affect L 3 concentration on herbage. In this study, L 3 remained aggregated close to the faecal pats they emerged from even after two successive harvests and significant rainfall. Successive harvests simulated the effect of repeated grazing events by a non-infective stock class. Two such grazings and the associated time, reduced L 3 presence on grazable herbage to <3% of the original population. Grazing strategies to generate clean pasture for vulnerable cattle are discussed in relation to these results.

SELECTIVIDAD DE VACAS LECHERAS EN PASTOREO POR CULTIVARES DE Lolium perenne L

The objective of this study was to determine the effect of herbage mass, metabolizable energy content, tiller density and dimensions on grazing selectivity, measured by grazing time and estimated herbage intake, on the ryegrass ingestive behaviour of lacting dairy cows. This study was conducted with ten L. perenne cultivars: Bronsyn SE, Bronsyn AR1, Impact, Impact AR1, Aries, LP 296, Arrow, Meridian, Matrix and Nui. During the establishment period, 35 kg of N, 228 kg of P2O5 and 123 kg of K2O were applied per ha and 30 additional kg of N were applied after each grazing event. When any L. perenne cultivar reached an average undisturbed sward surface height of 20 cm, all plots were harvested and then grazed, with no more than 60 days between harvests. After each grazing event, the trial was cut to a 4 cm stubble height. The undisturbed sward surface height and the herbage mass preand post-grazing, the estimated herbage intake, metabolizable energy content, tiller density, leaf length, leaf width, sheet weight and leaf weight were evaluated. Grazing behavior variables included only grazing time. The experimental design was a randomized block with 10 treatments (10 L. perenne cultivars) and 3 blocks. The results were analysed through ANOVA and the Waller - Duncan test was used to compare means. The cows did not discriminate among cultivars during the entire experiment, with no significant differences in grazing time and estimated herbage intake between cultivars. In general, there were no significant differences among cultivars in terms of: herbage mass, undisturbed sward surface height, metabolizable energy content, tiller density and dimensions, and any significant differences in these variables for some grazing events were not large enough to influence grazing selectivity.

Intensive rotational grazing assists control of gastrointestinal nematodosis of sheep in a cool temperate environment with summer-dominant rainfall

While rotational grazing methods have an accepted role in the management of gastrointestinal nematodosis (GIN) of small ruminants in humid tropical regions, their efficacy and application in cool temperate regions is more controversial. This study evaluated GIN over 2 years in three classes of fine wool Merino sheep (lambs, hoggets and ewes) under three different sheep management systems in a cool tableland environment near Armidale NSW Australia (950 m altitude, 30°31′S, 151°39′E). The management systems were High input (HI) with high fertiliser inputs, a target of 100% sown pasture, high stocking rate (13.4 dry sheep equivalents/ha) and relatively long grazing periods; Typical (TYP) New England management system with moderate fertiliser inputs and stocking rate (9.3 DSE/ha) and relatively long grazing periods; and Intensive rotational grazing (IRG) with moderate fertiliser inputs and stocking rate (8.8 DSE/ha) but very short (mean 5 days) grazing periods and long (mean 103 days) rest periods. Twenty sheep of each class in each management treatment were sampled monthly for faecal worm egg counts (WEC, followed by larval differentiation), and body weights with a blood sample taken for haematology every second month. The proportion of sheep with WEC above zero did not differ between management systems but the magnitude of WEC did, with sheep under IRG displaying lower mean WEC than those on the other treatments (IRG: 326, HI: 594, TYP: 536, eggs/g P < 0.0001). This was despite a significantly longer mean interval between anthelmintic treatments (IRG: 144 days, HI: 77 days, TYP: 78 days, P < 0.0001). The IRG management system also influenced the composition of the infections with sheep on this treatment having a significantly lower proportion of Haemonchus contortus in their faecal cultures (IRG: 59.7%, HI: 79.4%, TYP: 80.9%, P < 0.05) and a significantly higher proportion of Trichostrongylus spp. Sheep on the IRG treatment also had a significantly higher haematocrit (HCT) than those on the other management systems. Despite the lower WEC and higher HCT, sheep under IRG also had significantly lower bodyweights and fleece weights overall, although this was only evident in sheep raised to adulthood prior to the experiment, not those raised during the 2-year experimental period. The results demonstrate that IRG systems with short grazing periods and long rest periods between grazing events can assist with control of GIN in cool temperate climates where H. contortus is the dominant parasite.