Effects of grazing and precipitation on herbage production,herbage nutritive value and performance of sheep in continental steppe

The present study highlights the effects of sheep grazing and precipitation on herbage and animal performance in a grazed steppe of Inner Mongolia. Experimental data were collected during grazing periods of four consecutive years (2005–2008), and effects were analysed across a gradient of seven grazing intensities. Variation in annual precipitation, reflected by the effect of ‘year’, was the major factor affecting herbage; i.e., the production and nutritive value of herbage increased with increasing precipitation. Herbage parameters were also affected by grazing intensity, as herbage production (HP) and herbage nutritive yields decreased, while herbage nutritive values increased with increasing grazing intensity. The grazing‐induced decrease in herbage nutritive yields suggests that decreases in HP offset the positive effect of grazing on the nutritive value. Liveweight gain (LWG) was predominantly affected by grazing intensity, as LWG per sheep and per ha decreased and increased, respectively, with increasing grazing intensity. However, responses varied among years: LWG per sheep was maximized by light grazing in the drought year and by moderate grazing the wet year. Our results showed that herbage shortage at high grazing intensities reduces LWG per sheep and thus diminishes responses in LWG per ha. Nevertheless, the highest grazing intensity provides highest animal production per ha in the short term; however, this is not sustainable in the mid‐ and long term because decreasing HP induces degradation processes. Based on our results, a reduction in grazing intensity that still provides 78% of the maximum LWG per ha meets the requirements of a sustainable grazing management.     

Factors affecting grazing preference by sheep in a breeding population of tall fescue (Festuca arundinacea Schreb.)

A disadvantage of tall fescue (Festuca arundinacea Schreb.) is its low voluntary intake, resulting in suboptimal performance under grazing. Ideally, selection for this trait is done using grazing animals, but their use in plant breeding programmes is costly and laborious. Repeatable, stable and quantifiable traits linked to animal preference could ease tall fescue breeding. We established a trial to find relationships between the grazing preference of sheep and sward‐ and plant‐related traits. Seventeen genotypes were studied in swards. Sheep grazing preference, pre‐grazing sward height (SH), leaf softness, leaf blade length, width, colour and shear strength, and concentration of fibre, silica, digestible organic matter (DOM) and water‐soluble carbohydrate (WSC) were quantified throughout the growing season. The traits with the strongest correlation with sheep preference were DOM, SH, leaf colour, leaf width and WSC. Leaf softness, silica content and leaf shear strength were not correlated with sheep preference. We conclude that DOM is the trait that offers the best prospects for contributing to progress in tall fescue plant breeding for both intake and feeding value.     

Livestock‐type effects on biomass and nitrogen partitioning in temperate pastures with different functional‐group abundance

Livestock grazing can be a means to maintain biodiversity in grasslands, but the outcome for vegetation structure and species composition depends on livestock type and grazing regime. This study aims at disentangling the effects of plant functional‐group abundance and livestock type on the above‐ and below‐ground biomass and N allocation in temperate pastures. We investigated the effects of cattle, sheep and mixed stocking on above‐ground biomass (AGB) and belowground biomass (BGB) and plant N pools in a replicated grazing experiment in two pasture community types with different plant functional‐group abundance (diverse vs. grass‐dominated swards). In the six treatments, AGB was reduced up to 80% compared with an ungrazed control. Cattle reduced AGB to a larger extent than sheep in diverse pastures (80 vs 44% reduction) while sheep grazing tended to do so in grass‐dominated pastures (57 vs 46% reduction); mixed stocking led to intermediate values. Grazing reduced AGB more than the N pool in AGB, thus lowering the biomass C/N ratio relative to the ungrazed control. Neither BGB nor the N pool in BGB differed between the grazing treatments and the control plots. We conclude that livestock type and functional‐group abundance are interacting factors that influence plant biomass and N pools in swards of managed temperate pastures. The contrasting biomass removal rates of cattle and sheep could be used to increase the structural heterogeneity and total plant species pool of pastures by keeping different livestock species in neighbouring patches.     

Grazing preference of Merino sheep for naturalized annual clover species relative to commonly sown clover species

Selective grazing of white clover (Trifolium repens) over grass species in temperate pastures results in reduced clover abundance and availability over time. Within sheep‐ and cattle‐grazed dryland (<800 mm annual rainfall) hill and high country areas of New Zealand, naturalized unsown annual clover species show greater persistence and abundance over sown clovers. With a view to understanding legume abundance in these areas, Merino sheep grazing preference was investigated for pure swards of naturalized species Trifolium dubium, T. glomeratum, T. arvense and T. striatum and commonly sown species T. repens and T. subterraneum. The Chesson–Manly preference index was used to explore the hypothesis that grazing preference differs between these species and changes as plants mature. Herbage offtake was quantified at vegetative (mid–late spring; November) and reproductive (early summer; December) stages of plant maturity. Significant preference distinctions between species (P < 0·05) occurred in December, with relative preference ranging from 0·248 for T. repens to 0·065 for T. dubium. Reduced relative preference for naturalized species was related to decreasing nutritive value from spring to summer, reflecting increased stem and flower sward content. Relative preference was negatively related to increasing acid detergent fibre and neutral detergent fibre and positively related to greater crude protein and dry‐matter digestibility. Naturalized annual clover species of lower grazing preference at reproductive maturity will benefit pasture sustainability via herbage and seed production and associated nitrogen‐fixation inputs.     

Evaluation of tall fescue (Festuca arundinacea) as a forage for sheep in the temperate high‐rainfall zone of south‐eastern Australia

Tall fescue (Festuca arundinacea Schreb.) is currently seldom used in the high‐rainfall (>600 mm) zone of south‐eastern Australia. To determine its potential to improve forage availability during the summer‐autumn feed‐deficit period, a field plot‐scale experiment with sheep evaluated a Continental cultivar of tall fescue (cv. Quantum) at Hamilton, Victoria, between September 2006 and January 2009. Four grazing treatments represented set stocking or rotational grazing at the two‐, three‐ or four‐leaf stage, in a completely randomized design with three replications. Grazing treatment effects on tall fescue tiller population dynamics, forage accumulation rates and consumption, sward nutritive value and botanical composition were measured. Results showed tall fescue can persist and support year‐round grazing by sheep, subject to water availability for summer growth from summer rain or on moisture retentive heavy soils. During the summer‐autumn (December–April) vegetative phase, grazing at the three‐leaf stage optimized forage consumption, with no difference in feed value or botanical composition between the grazing treatments during these months. During the reproductive phase (September–November), feed value was highest under set stocking and declined with the production of each successive leaf. Grazing at the three‐ or four‐leaf stage prevented winter weed invasion, but winter forage consumption was low in these treatments. Set stocking or grazing at the two‐leaf stage improved winter forage consumption rates, but these swards were invaded by winter growing weeds.     

Nutritive value of herbage of five semi-irrigated pasture species across an irrigation gradient

As water resources become limiting, the need to produce stable amounts of herbage with a high nutritive value increases. An understanding of how levels of irrigation affect crude protein (CP) and neutral-detergent fibre (NDF) concentrations and, in vitro true digestibility (IVTD), is critical in the management of pastures. Smooth bromegrass ( Bromus inermis Leyss.), prairiegrass ( Bromus willdenowii Kunth), hybrid-bromegrass [meadow ( Bromus riparius Rehm.) × smooth bromegrass], creeping foxtail ( Alopecurus arundinaceus Poir.) and RS wheatgrass ( Elymus hoffmannii Jensen & Asay) were established under a line-source irrigation system to evaluate the effect of five water levels and three harvest dates on concentrations of CP and NDF, and values of IVTD. With CP concentration of herbage, there were positive linear significant relationships with decreasing water levels for all species. Rankings for mean CP concentrations across water levels and harvest dates were smooth bromegrass > RS wheatgrass > hybrid-bromegrass > creeping foxtail > prairiegrass. No consistent relationships with IVTD across water levels were detected among the species. Averaged across water levels, harvest dates and years, smooth bromegrass, hybrid-bromegrass and creeping foxtail had significantly higher IVTD values than RS wheatgrass and prairiegrass. Rankings of mean NDF concentrations across water levels and harvest dates combined over years were prairiegrass > RS wheatgrass > hybrid-bromegrass > creeping foxtail > smooth bromegrass. Herbage of smooth bromegrass had higher IVTD values and lower NDF concentrations than hybrid-bromegrass, prairiegrass, creeping foxtail and RS-hybrid at all water levels.     

Individual and socially learned preferences for biserrula (Biserrula pelecinus L.) in sheep

This study examined how sheep develop a learned aversion to the annual legume biserrula (Biserrula pelecinus L.). Merino sheep were grazed on paddocks sown with either (i) biserrula, (ii) biserrula + ryegrass (Lolium rigidum Gaud.), (iii) crimson clover (Trifolium incarnatum L.), (iv) crimson clover + ryegrass or (v) ryegrass, for 4 weeks. Relative preference (Chesson–Manly selection index) was determined by offering randomly ordered monoculture plots of the three forage species. The groups of sheep were then combined into a single group and grazed a paddock containing a monoculture sward of each plant type for 5 d. Relative preference of sheep was tested again after the completion of the combined grazing. The experiment was repeated at three stages of plant phenology: vegetative, reproductive and senesced. Relative preference for biserrula was lower in sheep that had grazed the paddock sown with only biserrula compared with sheep that grazed a combination of biserrula + ryegrass, at both the vegetative (α; −0·11 vs. 0·32) and reproductive (α; 0·18 vs. 0·63) stages. At each stage of phenology, when groups were combined and grazed together, preference for biserrula became uniform. This supported the hypothesis that sheep develop an aversion to biserrula when they graze a pasture containing biserrula. However, we concluded that the familiarity of sheep with biserrula did not result in low relative preference; rather, the aversion was more likely a response to the high proportion of this plant in their diet. Social facilitation may have enabled sheep to overcome rapidly the food aversion.     

Preferences of lambs offered Italian ryegrass (Lolium multiflorum L.) and barley (Hordeum vulgare L.) herbage as choices

Partial preference for feeds in ruminants is a well-documented phenomenon although their explanation can be elusive. The hypothesis was tested that sheep offered herbage of two annual grass species differing in chemical composition free-choice would select a diet that would maximize the nutritive value of the diet compared with sheep offered each herbage separately through a greater nutrient balance and synchronization of nutrient release for efficient ruminal microbial function. Fifteen male lambs were placed into metabolic cages, and randomly assigned to three treatments ( n  = 5): Italian ryegrass fresh herbage (treatment R), barley fresh herbage (treatment B) or free-choice Italian ryegrass and barley fresh herbage (treatment RB). Both herbages had similar crude protein concentrations but Italian ryegrass herbage had higher concentration of water-soluble carbohydrates and lower concentration of fibre than barley herbage. Lambs were exposed to the treatments for 15 d. Lambs on treatment RB showed a partial preference of 0·82 (s.e. 0·031) for Italian ryegrass. Lambs on treatment RB had higher intakes of digestible dry matter and higher values for nitrogen retention than lambs on treatment B although similar to that of lambs on treatment R. The results for the dietary choices were not always consistent with maximizing the nutritive value of the diet. Other explanations, such as lambs needed to sample and track the nutritive value of dietary options or there was the development of transient food aversions, were also possible.     

Effects of livestock breed and grazing intensity on biodiversity and production in grazing systems. 1. Nutritive value of herbage and livestock performance

Reduction of grazing intensity and the use of traditional instead of commercial breeds has frequently been recommended to meet biodiversity and production goals in sustainable grazing systems in Europe. To test the impact of such practices across a range of contrasting grassland types, integrated measurements of foraging behaviour, agronomic production and botanical, structural and invertebrate biodiversity were made over three years on four sites in the UK, Germany, France and Italy. The sites in the UK and Germany were mesotrophic grassland with high productivity and low to moderate initial levels of plant diversity, and were grazed by cattle. The French site was a semi‐natural, species‐rich grassland grazed by cattle. The Italian site contained a wider range in plant diversity, from species‐rich to mesotrophic grassland, and was grazed by sheep. The treatments were: MC, moderate grazing intensity with a commercial breed – this was designed to utilize herbage growth for optimum livestock production; LC, lenient grazing intensity with a commercial breed – this was designed to increase biodiversity by not fully utilizing herbage growth; and LT, lenient grazing intensity with a traditional breed – this was also designed to increase biodiversity. Neither fertilizers nor pesticides were applied. The nutritive value of the herbage and the performance of the livestock were measured. Mean stocking rates were proportionately 0·30–0·40 lower and mean sward heights and herbage mass on offer were 0·30–0·50 higher on the LC and LT treatments compared with the MC treatment. The proportion of live and dead material, and leaves and stems in the herbage, its chemical composition and nutritive value were little affected by the treatments. Individual livestock performance, measured as liveweight gain, showed no consistent response to treatment. In Germany, performance on the MC treatment was slightly lower than on the LC and LT treatments but no such difference was found on the sites in the other countries. Livestock breed did not have a strong effect on livestock performance. In the UK and France the traditional breeds had a lower performance but this was not the case in Germany or Italy. Livestock performance per ha of the LC and LT treatments was up to 0·40 lower than of the MC treatment. It is concluded that biodiversity‐targeted extensive grazing systems have potential to be integrated into intensive livestock production systems because the individual livestock performance reaches a similar level compared to a moderate grazing intensity. Traditional breeds did not have a production advantage over commercial breeds on extensively managed pastures.     

How do severity and frequency of grazing affect sward characteristics and the choices of sheep during the grazing season?

The effect of grazing frequency and severity on sward characteristics and preferences by sheep was investigated from April to September. Two levels of grazing severity were imposed by varying the numbers of ewes grazing 200 m² plots for 24 h: four (S, severe) or two (L, lax) ewes. Grazing frequency was either 1 d week^?1 (F, frequent) or 1 d every 2 weeks (I, infrequent). By combining frequency and severity, four treatments were obtained: SF, LF, SI and LI. The six binary combinations (SF/LF, SF/SI, SF/LI, LF/SI, LF/LI and SI/LI) were studied in preference tests. Treatments LF, SI and LI were characterized by a high sward surface height, biomass and amount of reproductive green tissues relative to treatment SF. Herbage quality was not different between the grazing treatments between April and July. In September, after a 6‐week period of regrowth, herbage quality was significantly higher for the SF treatment than the other treatments. The sheep preferred the swards grazed at a low frequency between April and July, and then changed their preference in favour of the sward with higher quality herbage (treatment SF). The relative abundance of green laminae and the relative digestibility of the swards helped to explain the preferences observed. For a low grazing pressure at the spatio‐temporal scale studied, sheep should graze swards at a relatively low frequency but at a high severity of grazing rather than the reverse.     

SHEEP GRAZING PREFERENCES ON A SALTINGS PASTURE AND THEIR SIGNIFICANCE FOR WIGEON (ANAS PENELOPE L.) CONSERVATION

Arising from the need to improve the palatability of tussocky, rank Festuca rubra swards to provide a greaer area of grazing for overwintering wigeon which avoided these swards, the effect of sheep grazing on these and close-mown F. rubra swards was studied by a point-quadrat method. This showed that close mowing improved the palatability of Festuca rubra swards for sheep to a degree comparable with swards made up of Puccinellia maritima and Agrostis stolonifera, for which sheep and wigeon had previonsly been shown to have a significant preference. The results of the study are discussed in relation to methods of managing an area of saltings pastnre made up of these two types of swards to increase the area of grazing available for wigeon; whilst still being compatible with the objectives of the grazier's sheep husbandry.     

Changes in the herbage nutritive value and yield associated with threshold responses of vegetation to grazing in Mongolian rangelands

We examined the changes in the nutritive value and yield of herbage along a grazing gradient, where abrupt changes in community composition occurred, at multiple ecological sites in Mongolian rangelands. At grassland sites, changes in the herbage nutritive value could be attributed to rapid replacement of perennial grasses or forbs with weedy annual forbs along a grazing gradient. Crude protein (CP) concentration increased sharply in approaching the source of grazing gradient, whereas neutral detergent fibre and metabolizable energy (ME) concentrations decreased sharply. As ME can be utilized as a main index of herbage nutritive value, these results indicated its overall loss with severe grazing. Consequently, gradual increases in the yields of CP and ME in the direction of the gradient source at the grassland sites did not necessarily indicate the improvement of rangeland condition. In contrast, at shrubland sites, we could not generally detect any significant trends in the herbage nutritive value. The yield of ME gradually decreased in the direction of gradient source, suggesting that grazing affects herbage yield rather than herbage feed value at shrubland sites. Thus, the nutritive value and yield of herbage can be modified greatly in association with nonlinear responses of vegetation to livestock grazing.     

Short-term impact of grazing by sheep on vegetation dynamics in a newly created salt-marsh site

The effects of grazing by sheep at a stocking density of c. 1 sheep ha⁻¹ from August to April on total vegetation cover, diversity of plant species, above-ground plant biomass and concentration of crude protein, neutral-detergent fibre and acid-detergent fibre of salt-marsh vegetation was assessed over a 2-year period on a newly created salt-marsh area on the Belgian coast. Assessments were made in both grazed and ungrazed areas in four elevation zones: low, intermediate, high and floodmark zone. The cover of dominant salt-marsh species ( Salicornia europaea , Limonium vulgare and Elymus athericus ), plant diversity, plant biomass and chemical composition of herbage were compared between grazed and ungrazed plots, and between 2005 (initial state) and 2007 (after a 2-year grazing period) using paired t -tests. Grazing by sheep maintained plant diversity in the high zone, whereas diversity decreased in the ungrazed plots. Grazing had no apparent effect on total vegetation cover and composition of the vegetation. Concentration of crude protein in herbage increased and that of neutral-detergent fibre decreased in the high and intermediate zones. Expansion of the dominant species of the high zone, E. athericus , was not affected by the stocking density used in the study.     

Social network analysis of sheep grazing different plant functional groups

Social Network Analysis (SNA) is used for the first time to investigate the relations between plant functional groups and social structure of grazing sheep. The research was conducted on a grassland in Crete's island Lefka Ori, Greece during 2016. A flock of 20 sheep of Sfakion race was analysed as a network and the sheep as nodes. The focal sampling technique was applied during four experimental periods of four consecutive days × eight hours/day. The plant species selected by sheep during grazing were categorized into four functional groups (grasses, broad‐leaved forbs, shrubs and trees), and the proximity and conflict relations that were developed among the flock members were recorded. The tools of SNA were defined and interpreted in the sheep flock, and the Visone software is used to calculate the network variables of proximity and conflicts relations of nodes. Correlations between the plant functional groups and network variables were examined by Spearman's bivariate correlation test. Sheep collectivity was enhanced while grazing grasses and simultaneously, a tendency for hierarchization within the flock was identified. Similarly, the proximity of sheep increased during forbs’ grazing while their individualism was strengthened. When grazing shrubs, the proximity of sheep was only in part maintained while the grazing of trees seems as the most deconstructive forage option of sheep proximity relations. In general, the grazing of all plant functional groups decreases conflicts among sheep except that of trees, which was insignificant for developing such relations.     

高产优质饲用玉米生产技术研究

系统研究了不同栽培措施对玉米饲用营养价值的影响。研究结果表明,不同类型玉米品种鲁单50、高油115和科多4号的饲用营养价值有显著差异;适宜的种植密度,特别是适宜的高种植密度条件下喷施植物生长调节剂、合理施肥、适时抑制玉米的生殖生长、在乳熟末蜡熟初期适时收获可以显著提高玉米的饲用营养价值。     

Seasonal dynamics of biomass production and herbage quality of three grasslands with contrasting functional compositions

Classifying grasses into plant functional types (PFT) according to their strategy of nutrient capture (PFT A, B and b) or nutrient conservation (PFT C) is claimed to predict variability in biomass production and herbage quality in grasslands. PFT A, B and b are characterized by higher production than PFT C, with higher nutritive value, which decreases rapidly. PFT C is characterized by lower nutritive value, which remains more stable in time. The aim of this study was to quantify the consequences of PFT composition at the community level on the seasonal dynamics of biomass and herbage quality for livestock feed. We studied three grasslands located in the same area with contrasting PFT composition and classified PFT A, PFT Bb and PFT C. The dynamics of vegetation stages, dry‐matter yield and nutritive value were followed over three vegetation cycles in 2007–2008. In the first cycle, biomass accumulation was high for the PFT A and PFT Bb grasslands and the high quality of herbage declined rapidly with the reproductive development. By contrast, biomass accumulation was slow in the PFT C grassland, with a lower quality that declined slowly, consistent with the later reproductive development. For regrowth cycles, the same ranking of grasslands was observed for biomass accumulation, and differences in digestibility were similar to those observed at the beginning of the first vegetation cycle. Combining type of grassland with sum of temperature for the first cycle and regrowth days for the second and third vegetation cycles provided quantitative models of herbage biomass and quality.     

The conservation management of mesotrophic (meadow) grassland in Northern England. 2. Effects of grazing, cutting date, fertilizer and seed application on the vegetation of an agriculturally improved sward

The plant species number and composition, iind yield of herbage biomass of an agriculturally improved hay meadow were assessed after 4 years under various combinations of grazing, fertilizer applicution. cutting date and seed addition treatments in a replicated split-plot design. Grazing treatments consisted of either autumn grazing with cattle and sheep, spring grazing with sheep or both regimes. Fertilizer application treatments consisted of either 25 kg ha^?1 N plus 12–5 kg ha^?1 P and K or no fertilizer. Cutting date treatments consisted of cuts on either 14 June, 2i July or 1 September. Seed addition treatments consisted of either no addition or sowing with a range of meadow species in the autumn. Data analysis was by correspondence analysis and analysis of variance. Species number decreased with fenilizer use and when the cutting date was 1 September. A range of species was affected by the main treatments and there were some first-order interactions, mainly between cutting date and fertilizer application. Rhinanthus minor was particularly favoured by the seed addition treatment. Species attnbutes in the regenerative and established phase were related to treatments and their effect on species composition. The National Vegetation Classification communities were associated with particular treatment regimes. The 21 July cutting date favoured ‘improved’ over ‘unimproved-traditional’ swards, with spring grazing favouring ‘unimproved-traditional’ swards. Lowest yields of herbage biomass were associated with autumn and spring grazing, the 14 June cutting date and no fenilizer treatments. The fenil-izer, 1 September cutting date and auiumn grazing treatments gave the highest yields. The implications of these results are discussed in terms of the conservation management required to return agriculturally improved mesotrophic grassland to a species composition similarto that of traditionally managed grassland.     

Mixed‐grass prairie rhizome biomass is influenced by cattle grazing intensity

This study was conducted on a mixed‐grass prairie in south‐central North Dakota, USA, to test the effect of animal grazing on rhizome biomass. Below‐ground plant biomass samples were collected from pastures with moderate and heavy grazing by beef cattle. Because the biomass data did not meet the normality assumptions, the computer resampling method involving a nested anova was used. A reduction in rhizomes was found under heavy grazing, as compared with moderate grazing. Although rhizomes only accounted for a small fraction of total below‐ground plant biomass, our study suggested that the high rhizome density found in the moderately grazed pastures might be partly responsible for the greater potential of plant regrowth in the moderately grazed pastures than in the heavily grazed pastures on this mixed‐grass prairie.     

Forage selectivity by cattle and sheep co‐grazing swards differing in plant species diversity

Interactions between sward diversity and forage selectivity of cattle and sheep managed within mixed grazing systems are not fully understood. The objective of this study was to investigate the effect of either mono‐ or co‐grazing of sheep and cattle on swards differing in botanical composition (either diverse or grass‐dominated) on the intake choices of six target forage species. Jacobs' selection index (JSI) was employed to quantify the preference for single target species in relation to their proportion in the sward. Results revealed distinct intake preferences of sheep and cattle; as expected, sheep were more selective than cattle. To a lesser extent, the sward composition had an effect on intake preferences: cattle responded to botanical composition by changing their intake preferences, but to a lesser extent than sheep. Phleum pratense was the most preferred target forage species (JSI = 0.62). Lolium perenne, Taraxacum sect. Ruderale and Trifolium repens were also highly preferred regardless of sward composition or type of grazing (JSI = 0.47, 0.32 and 0.27 respectively). Dactylis glomerata and Festuca pratensis tended to increase in abundance after grazing events in both diverse and grass‐dominated swards. Co‐grazing of cattle and sheep facilitated a more homogeneous consumption of the target forage species evaluated.     

Grazing by sheep and the distribution of species through the canopy of a red clover-perennial ryegrass sward

A trial was carried out to investigate whether or not sheep grazing at stocking rates of 22 (low) and 44 (high) ha⁻¹ select red clover from a red clover-perennial ryegrass sward, The distribution of botanical and morphological components was assessed in consecutive 5-cm layers through the canopy inside and outside exclosure cages moved every 2 weeks for 6 weeks. The difference between inside and outside cages for a given layer was an indication of the amount of each component consumed from that position in the sward, and the corresponding difference for clover content was considered an indication of selection.
Evidence of selection was observed over the third and fourth weeks of grazing, especially in the high stocking rate treatment. Laminae of red clover were selected in preference to other plant parts and were grazed throughout the depth of the canopy in contrast to grass. The basal layer at the high stocking rate during weeks 5 and 6 was not grazed suggesting that the crown of red clover may be protected from severe overgrazing by accumulation of dead matter.
It was concluded that the low herbage density of red clover-grass swards allowed the occurrence of selection which was most pronounced when the sward was being grazed down relatively quickly.