New Approaches and Tools for Grazing Management

Novel concepts and tools to promote progress in grazing science and management need to incorporate heterogeneity and nonlinear scaling of spatially and temporally distributed ecological interactions such as diet selection, defoliation, and plant growth. Traditional grazing management factors are number of animals, species and category of animals, spatial distribution of forage demand, and temporal distribution of forage demand. These traditional methods have been based on a paradigm that is static, assumes equilibrium conditions, and does not consider scaling issues, neither in time nor in space. Three related issues that can contribute to the progress in the understanding and management of grazing systems are spatial heterogeneity, event-driven dynamics, and scaling effects. Spatial heterogeneity of species and defoliation determine pasture stability by modulating competition and response to heterogeneous defoliation. When pasture species are well mixed, livestock are less able to select their preferred diet. When species are separated into larger and more easily identifiable patches, the selected diet approaches the preferred one. Simultaneously, patchiness in pasture components and redistribution of nutrients by grazing can lend global compositional stability to grass–clover pastures. Grazing at high animal density can be studied using the paradigm of event-driven dynamics. Several mechanisms suggest that grazing systems should have allometric spatial and temporal scaling in addition to the well-recognized allometric scaling of food requirements with body mass. Grazing system performance should scale allometrically with pasture size because both resource distribution and animal movements frequently have fractal properties. As pasture size increases, fewer hierarchical levels of grazing behavior are constrained, and the new spatial patterns introduce nonlinearity in the response to pasture size. Operant conditioning of foraging behavior, conditioned aversions, plant spatial pattern, pasture size and shape, timing and duration of grazing periods, and number of animals are discussed as precision tools to manage grazing systems.     

中国北方草地生态系统管理问题与对策

草地具有生态意义、资源意义和生物进化场所及文化意义。北方草地表观表现为"三化",草丛对地面的覆盖力和产量是一般采用的判定指标,缺乏生态系统结构要素和功能受损的评价标准,农田化也是草原被破坏或消失的重要因素。放牧是家畜生产途径,也是草地管理手段。放牧干扰状况包括放牧开始时间、放牧强度、放牧频次和持续时间,放牧要素包括啃食、践踏、口液和失衡营养。载畜量或草畜平衡的方程体系中缺少牲畜生长状态参数,草地管理的一项重要内容是管理草地放养的家畜,发展豆科混合半人工草地,以维护土壤肥力,增加牲畜日粮的粗蛋白含量应该是中国北方草地管理当前与今后一段时期内的重要研究内容。草地管理,即草地生态系统管理是由明确目标驱动,由政策和协议及实践而执行,以对生态作用与过程的理解所需的研究和监测为基础,而保持生态系统组分、结构和功能正常运行的管理。     

The effect on wool production of changes in management designed to increase output of lamb from hill land in the United Kingdom

A system of management designed to increase the economic efficiency of the production of weaned lamb from hill land through the use of pasture improvement and controlled grazing has resulted in considerable increases in the outputs of both lamb and wool. In two examples quoted the weight of weaned lamb produced increased by 51 and 94%; these changes were accompanied by increases in wool output of 31 and 84%, respectively. The additional outputs of both products are attributable to a combination of increased numbers of ewes and higher levels of individual animal performance.The increase in output of wool which may be expected from changes in management directed at increasing lamb production is relatively small, ranging from 4.6 to 6.5 kg per 100 kg increase in weaned lamb in the Scottish Blackface to 11.6 kg per 100 kg increase in weaned lamb in the South Country Cheviot. Evidence is presented to show that the magnitude of the increase in wool production is likely to be determined genetically by the response to improved nutrition of both lamb and wool production.     

Grazing management as it affects nutrition, animal production and economics of beef production

Until recently, the nutritional fate of the grazing animal has been largely ignored by both animal and range scientists despite the economic dependence of the extensive livestock industry on nutrition from grass. Of the three factors that can be manipulated to improve profit gross margin per animal, is one that is directly affected by nutrition and, hence, grazing management. The relationship between economics and grazing management may be summarized as: Gross margin = f(Animal Performance); Animal Performance = f(nutrition); Nutrition = f(grazing). Economical beef production must consider the needs of the animal and the forage plant at the same time. The health of the sward must be maintained while improving individual animal performance and simultaneously increasing stocking rate. Generally, plants that have been defoliated require a period of recovery before again being grazed. A sward is kept in a vigorous state by preventing repetitive defoliation at the one extreme, and avoiding excessive shading (mature growth) of photosynthetic material at the other. This state is best achieved where livestock grazing is controlled. For any individual paddock, periods of grazing are followed by periods that allow adequate physiologic recovery of the plants. A grazing regimen that keeps the plant in a healthy state is fortuitously also well suited to the nutritional requirements of the animal. Animals on overgrazed pastures are likely to suffer from inadequate feed intake because of deficiencies in feed quantity. Conversely, on over-rested pastures, intake deficiency results from paucity in feed quality. On most unmanaged ranges, overgrazed and over-rested plants are likely to be found side by side. By controlling duration of the rest period as well as duration of the grazing period through pasture subdivision, requirements of both the plant and the animal can be met. With artificially high economic demands placed on animal production, some form of supplementation is required in most modern livestock situations. Whereas energy is frequently the nutrient limiting production it is seldom economically feasible to supplement the grazing animal directly with energy. Protein supplementation to increase forage intake, and thus indirectly energy intake, has become standard practice in many grazing situations. When there is adequate forage with a low crude protein content (less than or equal to 7%), microbially degradable protein is the preferred choice. However, when the animals are in an energy deficient state, either through a shortage of available forage or because their requirements exceed energy intake levels, by-pass protein is required.     

Advances in pasture management for animal productivity and health

A wide range of management techniques is available to enhance quantity and quality of forage supply to grazing animals throughout the annual production cycle. Within broad limits, dry matter (DM) production is relatively insensitive to management of defoliation frequency, severity and duration. However defoliation management has effects on feed quality which can be enhanced, in particular, by control of pasture growth in the spring through maintenance of relatively low average pasture masses. Treading damage can have significant immediate and ongoing effects on pasture production and farmers can use a range of management techniques to minimise these. Fertiliser application practices have a potent influence on pasture production and seasonality of that production. Available soil nitrogen is the primary nutrient deficiency limiting production in New Zealand's characteristically grass-dominant pastures. Nitrogen fertiliser usage has increased markedly in recent years, particularly to grow substantially greater amounts of forage during the cool season, and this trend looks set to continue. However, the use of nitrogen fertiliser has important environmental implications. Pasture renewal and forage crop use has also increased in recent years. Care needs to be taken in conducting cost-benefit analyses, selecting the options that best meet the needs, and in establishment and subsequent management practices. Ryegrass (perennial and hybrids) and white clover remain the primary choice for permanent pasture renewal, the availability of safe endophytes having largely alleviated effects of endophyte toxicosis. Special-purpose mixtures are used, especially in dry environments. Italian ryegrasses, brassicas and chicory are common choices for forage crops. A range of management techniques can be used to alleviate deleterious effects of some forages, including ryegrass endophyte toxicosis, facial eczema, and toxins associated with Fusarium fungi. Generally these techniques are not totally effective. More research is required to increase our understanding of these disorders, and in order to develop more effective and reliable management practices.     

Advances in pasture management for animal productivity and health

A wide range of management techniques is available to enhance quantity and quality of forage supply to grazing animals throughout the annual production cycle. Within broad limits, dry matter (DM) production is relatively insensitive to management of defoliation frequency, severity and duration. However defoliation management has effects on feed quality which can be enhanced, in particular, by control of pasture growth in the spring through maintenance of relatively low average pasture masses. Treading damage can have significant immediate and ongoing effects on pasture production and farmers can use a range of management techniques to minimise these.

Fertiliser application practices have a potent influence on pasture production and seasonality of that production. Available soil nitrogen is the primary nutrient deficiency limiting production in New Zealand's characteristically grass-dominant pastures. Nitrogen fertiliser usage has increased markedly in recent years, particularly to grow substantially greater amounts of forage during the cool season, and this trend looks set to continue. However, the use of nitrogen fertiliser has important environmental implications.

Pasture renewal and forage crop use has also increased in recent years. Care needs to be taken in conducting cost-benefit analyses, selecting the options that best meet the needs, and in establishment and subsequent management practices. Ryegrass (perennial and hybrids) and white clover remain the primary choice for permanent pasture renewal, the availability of safe endophytes having largely alleviated effects of endophyte toxicosis. Special-purpose mixtures are used, especially in dry environments. Italian ryegrasses, brassicas and chicory are common choices for forage crops. A range of management techniques can be used to alleviate deleterious effects of some forages, including ryegrass endophyte toxicosis, facial eczema, and toxins associated with Fusarium fungi. Generally these techniques are not totally effective. More research is required to increase our understanding of these disorders, and in order to develop more effective and reliable management practices.     

Influence of grazing management on the production of an irrigated grass/legume pasture in the Rûens area of the Southern cape

Abstract

The production of an irrigated grass/legume pasture was determined using Merino ewes on rotational and continuous grazing systems. The clover content of the pasture declined, while the grass content increased under both systems. The lucerne content of the rotationally‐grazed pastures did not change, but lucerne failed to persist under continuous grazing. Rotational grazing resulted in a lower clover content and, consequently, in a lower production per individual animal at low stocking rates during two seasons, but in a higher pasture production and grazing capacity, than under continuous grazing. At high stocking rates the individual animal production was, however, highest under rotational grazing, resulting in a higher animal production per ha than under continuous grazing.     

苜蓿放牧地生产性能与管理

苜蓿(Medicago sariva)放牧草地以其成本相对低、营养价值高、家畜生产性能优异而得到生产者的青睐.但用于干草的苜蓿不耐践踏,不适合放牧,而且家畜鼓胀病也限制其利用,因而使之成为苜蓿科研的新方向.有关放牧型苜蓿品种的选育以及家畜鼓胀病的管理研究,笔者将分别在其他文章中阐述.本文主要就苜蓿放牧地的管理(放牧方式、时间和强度)、合理利用及其对不同家畜生产性能的影响,以及目前育成的放牧型苜蓿品种进行综述,以期为苜蓿放牧的管理和利用提供参考.     

Effects of selective defoliation and height of defoliation on tiller dynamics and herbage yield of Themeda triandra in a semi-arid rangeland in Zimbabwe

Understanding the impacts of intensity and selection of grazing on the performance of grasses is important in the management of grazing areas. It is especially important in semi-arid environments where, apart from moisture, the levels at which grasses are utilized has a major influence on their persistence in the environment. The effects of selective defoliation and height of defoliation (5 cm and 10 cm stubble heights) on the performance of the grass, Themeda triandra, were investigated in a field experiment for two growing seasons. Performance was measured as tiller production, rate of production, tiller mortality, herbage yield and quality. Tiller production was greater (81 tillers per plant) under non-selective defoliation than under selective defoliation (49 tillers per plant) in the 1995/1996 season. Tiller mortality was higher (66.45%) under heavy selective defoliation than under nonselective defoliation (21.98%). Herbage yield, apart from the control treatment, was high (13.6 g per plant) under light non-selective defoliation. Heavy selective defoliation reduced the nutrient levels (e.g. levels of soluble carbohydrates under heavy selective defoliation were 6 g kg^?1 glucose compared to 20 g kg^?1 glucose under light non-selective defoliation).     

林,草,畜生态系统生物生产力及其相互关系

阐述了林、草之间和草、畜之间的关系。林草互相竞争,又互相受益。森林影响光照,从而影响草地产草量,但一定密度的森林对含蓄土壤水分,减少牧草蒸发,保持草地气温、土温稳定,对牧草生长有益。而草地的管理、施肥、放牧牲畜的粪尿、牧草的固氮作用等,又促进了森林的生长。草地产草量的季节性变化,可影响放牧牲畜的增重与繁殖。草地的载畜量取决于草地的产草量,草地负荷过重,可导致草地退化,放牧牲畜的生产性能下降,但适宜的载畜量可提高放牧牲畜的生产性能,保持草地的良性演替,延长草地的利用年限。     

Efficiency of feeding Duddingtonia flagrans chlamydospores to grazing ewes on reducing availability of parasitic nematode larvae on pasture

Gastrointestinal nematodes are of concern in sheep production because of production and economic losses. Control of these nematodes is primarily based on the use of anthelmintic treatment and pasture management. The almost exclusive use of anthelmintic treatment has resulted in development of anthelmintic resistance which has led to the need for other parasite control options to be explored. The blood sucking abomasal parasitic nematode Haemonchus contortus causes severe losses in small ruminant production in the warm, humid sub-tropic and tropics. This study evaluated the effectiveness of a nematode trapping fungus, Duddingtonia flagrans, in reducing availability of parasitic nematode larvae, specifically H. contortus, on pasture. Chlamydospores of D. flagrans were mixed with a supplement feed which was fed daily to a group of crossbred ewes for the duration of the summer grazing season. A control group was fed the same supplement feed without chlamydospores. A reduction in infective larval numbers was observed in fecal cultures of the fungus-fed group. Herbage samples from the pasture grazed by the fungus-fed group also showed a reduction in infective larvae. There were no significant (P > 0.05) differences in overall fecal egg count, packed cell volume or animal weight between fungus-fed and control groups. Tracer animals were placed on the study pastures at the end of the study to assess pasture infectivity. Although tracer animals were only two per group, those that grazed with the fungus-fed group had substantially reduced (96.8%) nematode burdens as compared to those from the control group pasture. Results demonstrated that the fungus did have activity against nematode larvae in the feces which reduced pasture infectivity and subsequently nematode burdens in tracer animals. This study showed that D. flagrans, fed daily to grazing ewes, was an effective biological control agent in reducing a predominantly H. contortus larval population on pasture.     

Integrated and biological control of parasites in organic and conventional production systems.

Organic and other non-intensive animal production systems are of growing importance in several countries worldwide. In contrast to conventional farms, parasite control on organic farms is affected by several of the prescribed changes in management e.g. access to the outdoors in the summer and in most countries, a ban on preventive medication, including use of anti-parasiticides. Organic animal production relies heavily on grazing, and pasture or soil related parasites are thus of major importance. Several studies in northern temperate climate have indicated that outdoor production of pigs, primarily sows, and laying hens results in heavier and more prevalent helminth infections compared to conventional intensive production under indoor conditions. In organic dairy cattle, parasitic gastroenteritis in heifers may be more prevalent. In a short to medium term perspective, integrated control may combine grazing management with biological control using nematophagous micro-fungi, selected crops like tanniferous plants and on conventional farms, limited use of anti-parasiticides. At present, the non-chemotherapeutic control of pasture related infections is based mainly on grazing management strategies. Preventive strategies, where young, previously unexposed stock, are turned out on parasite-free pastures, can be used for grazing first season dairy heifers and in all-in-all-out poultry production. Evasive strategies aim at avoiding disease producing infections of a contaminated area by moving to a clean area and may be relevant for ruminants and pigs. In cattle, effective control of nematodes can be achieved by repeated moves of the herd or alternate grazing with other species. High stocking rates seem to be an important risk factor. In pig production, the effect of paddock rotation on parasite infections is largely unknown and studies are warranted. Control of nematodes by larvae-trapping fungi, or perhaps in the future by egg-destroying fungi, looks promising for ruminants and certain monogastric animals but delivery systems and practical dosing regimes integrated with grazing management have to be developed. In conclusion, good prospects are expected for acceptable parasite control without a heavy reliance on anti-parasiticides through integration of the above mentioned procedures but future studies are needed to confirm their efficacy under practical farming conditions.     

Rotational Grazing Systems and Livestock Grazing Behavior in Shrub-Dominated Semi-Arid and Arid Rangelands

Rotational grazing systems (RGS) are often implemented to alleviate undesirable selective grazing by livestock. At both fine and coarse scales, livestock selectively graze individual plants, patches, communities, and landscapes. Smaller pastures, increased stocking density, and rotation allow managers to constrain livestock movement and determine season and frequency of grazing, potentially limiting selectivity and preventing repeated grazing of preferred plants. However, in arid and semi-arid rangelands, forage growth is limited primarily by precipitation rather than defoliation frequency. When soil moisture is adequate, forage is abundant and defoliation levels are typically low, and repeated, intensive defoliation of preferred plants is less likely than in more mesic areas where more consistent precipitation and soil moisture storage allows animals to establish and maintain spatial hierarchies of grazing patterns. Many southwestern rangelands contain diverse vegetation, which provides quality forage during different times of the year. These spatial and temporal patterns of forage distribution may not be amenable to manipulation with RGS. Tracking data show that livestock often alternate among locations within pasture boundaries and can opportunistically exploit areas with higher quality forage when they are available. Higher stock densities combined with higher stocking rates can increase livestock use of less preferred areas, but overall distribution patterns of intensive-rotational and extensive grazing systems are often comparable at similar stocking rates and distances from water. Management that ensures that grazing of riparian areas does not occur during the critical late summer period may be more beneficial than RGS that periodically defers livestock use throughout the grazing season. In arid and semi-arid shrublands, timely adjustments to animal numbers and practices that improve grazing distribution at regional and landscape scales are more likely to be effective in maintaining or improving rangeland health than fencing and RGS.     

Defoliation effects on perennial grasses — continuing confusion

Although an adequate knowledge of growth patterns and defoliation effects in perennial grasses is a prerequisite for the rational use of veld and pastures for animal production, our knowledge of this subject is far from adequate. The results of various physiological and clipping studies on tropical and subtropical grasses are appraised and their weaknesses in providing information applicable in practical management are indicated. It is suggested that there is a need for increased emphasis on studies of growth patterns and defoliation effects giving priority to (a) defining and evaluating the extrinsic and intrinsic factors affecting differential response to similar defoliation treatments in different circumstances, (b) applying defoliation treatments with a practical bias, and (c) determining actual defoliation patterns under grazing.     

Defoliation Intensity and Simulated Grazing Strategy Effects on Three C4 Rangeland Bunchgrasses

Defoliation intensity and timing are two important factors determining plants response to grazing. These factors can be managed by adjusting stocking rate and applying a grazing strategy. In a 6-yr clipping experiment conducted in northwestern Argentina, we assessed the effect of different defoliation intensities (~ 30%, ~ 50%, and ~ 70% removal of the annually produced aboveground biomass) and simulated grazing strategies (continuous grazing, two-paddock rest-rotation, three-paddock rest-rotation, dormant season grazing) on plots of three C4 native bunchgrasses (Pappophorum vaginatum, Trichloris crinita, and Digitaria californica). Response variables were mean and trend of clipped-off biomass during the 6 yr of treatments, number of inflorescences, and aboveground biomass produced on the year following treatments end (to evaluate residual effect of treatments). Results were species dependent. Mean clipped-off biomass increased with defoliation intensity in T. crinita and D. californica. However, defoliation intensity negatively affected clipped-off biomass trend in T. crinita and the production of P. vaginatum and T. crinita during “residual effect” evaluation. The three species responded positively at least in one response variable to the amount of rest periods in the grazing strategy. Our results are not fully consistent with the concept that forage production is more influenced by defoliation intensity than by grazing strategy: In two of the three species, grazing strategy presented greater impact on response variables than defoliation intensity. When significant “defoliation intensity × grazing strategy” was detected, intensity tended to be more detrimental as grazing strategy allows fewer rest periods. We observed a residual effect of treatments in the three species (generally, negative effect of defoliation intensity and positive effect of grazing strategies with more rest periods). Our results show that dormant season utilization and rest periods are beneficial for maximizing mean clipped-off biomass and ensuring clipped-off biomass trend. High defoliation intensities can maximize short-term clipped-off biomass, but it may produce negative residual effects and trends.     

Recent progress in the study of behavior and management in grazing cattle

Recent progress in studies concerning behavior of, and management for, grazing cattle are reviewed. Since 1950, much study has been conducted on ‘How’, ‘When’, ‘Where’ and ‘How long’ regarding grazing. After the 1980s, grazing ecology introduced the concept of hierarchy at different spatial and temporal scales, and since then grazing behavior has been investigated on the foraging hierarchy of large grazing herbivores: bite, feeding station (FS), patch, feeding site, camp and home range. From the sequence of activities, FS is grouped within a feeding patch, and movement of grazing cattle has been studied between FSs, feeding patches, feeding sites and between camps. Grazing behavior and production relates closley with defoliation, and grazing management should control both grazing behavior and vegetation according to three rules: planning, operational and adaptation rules. Planning rules relate the stocking rate of cattle; operational rules relate to defoliation; and adaptation rules vary with regional situations. Recent studies on grazing have been carried out in the fields of animal diversity and welfare. Future studies in this field should be conducted on the ecology, neurophysiology and psychology of grazing. Nonlinear analysis will also be significant in this field. Grazing cattle production should also utilize supplementation by roughage and/or grains.     

Seasonal changes in pasture biomass and grazing behaviour of cattle in the Guinea Savanna agroecological zone of Ghana

Spatial and temporal availability of pasture vegetation and cattle grazing behaviour in three seasons (intermediate season [IM], peak season [PS] and dry season [DS]) in the Guinea Savanna agroecological zone of Ghana was examined. The frequency of occurrence of three species groups (grass, legume and forbs) and biomass yield was estimated in 1 m² plots. The grazing behaviour of 18 cows from six herds was monitored over three days per animal. Season affected the prevalence of species groups with grasses being most dominant in all seasons. Most grazing lands were heavily grazed in IM and DS but moderately grazed in PS. Whilst harvested rice fields represented the most frequently grazed land in DS, fallowed hard pans were used in PS and IM. Biomass yield was highest in DS owing to the contribution of crop residues from harvested farmlands. Carrying capacity was linked to biomass production and averaged 0.55 in DS, 0.38 in PR and 0.21 in IM. Animals spent less time outside the kraal in PS than IM and DS. Walking time was higher in DS than in IM and PS. Less than 20% of the time on pasture was spent on resting, watering and social interaction across seasons.     

Mixed livestock grazing in diverse temperate and semi-arid environments

The need for an annual increase of 2% in global food production demands knowledge on how best to use natural grazing land resources. Taken with the requirement to protect resources, this need creates conflicting demands on grazing land management. Concerns for product quality, uniformity and continuity and for animal welfare will increasingly drive production processes. In this paper, the potential of mixed grazing for higher output of quality animal products, within these constraints, is assessed under both temperate and semi-arid conditions. Complementary behavioural patterns between domestic livestock types, particularly in their dietary selection, appear to be the primary basis for development of improved grazing ecosystems. Many of these processes operate at the landscape scale. In addition to increasing animal output, mixed grazing can be used to modify the vegetation. This is of particular importance for manipulating woody species cover in semi-arid areas and hence for improvement of range condition. For rural development, identification with the system and confidence in the purveyor sets the basis for success.     

Enhancing the profitability of pasture-based dairy production in the humid tropics through improved nutrition

Dairy production in the tropics represents a major challenge, especially when reliant on grazed forages, because of the conflicting factors of a high nutritional demand to sustain lactation on the one hand, and the relatively low quality of tropical grasses and a stressful environment, on the other. This paper focuses primarily on those tropical situations where grazed pasture is the cheapest feed resource. Effective management of the pasture as well as the animals that graze it is required in order to maximize economic viability of the farming enterprise. Feed planning helps to ensure that pasture use is maximized, either directly by grazing or, where profitable, indirectly by cutting for conservation. High rates of pasture utilization at each grazing minimize pasture senescence and decay and ensure that pasture remains in a vegetative state of the highest possible nutritional quality. Total annual feed requirements of the grazing herd must therefore be matched as closely as possible to the total annual pasture production on the farm. Stocking rate is critical in this regard, and is the single most important determinant of productivity in pastoral farming. Periods of pasture surplus or deficit will inevitably arise, but can be minimized by matching the monthly feed requirements of the herd as closely as possible to the monthly feed production on the farm. Herd requirements can be influenced, for example, through altering calving patterns and drying off dates. Even with good pasture management practices, it is highly likely that tropical pasture quality will be low for part of the year. Utilization of low-quality forages can be improved through the appropriate use of feed supplements, and the key principles are discussed. Firstly, conditions for optimum fermentative digestion in the rumen must be promoted through adequate provision of fermentable energy and nitrogen as well as essential minerals, such as phosphorus and sulfur. Further supplementation with metabolizable energy or protein, depending on what limits animal production, may be profitable. Various practical supplementation strategies for tropical forages are discussed. Finally, some suggestions for future research and development for enhancing the profitability of pasture-based dairy production in the humid tropics are made.