Grazing has existed since the beginning of agriculture. According to the Food and Agriculture Organization, about 60% of the world’s grasslands (slightly less than half of the world’s land area) are covered by grazing systems. Grazing systems provide about 9% of the world’s beef production and about 30% of the world’s sheep and goat meat production. For about 100 million people in arid areas and probably a similar number elsewhere, grazing livestock is the only possible source of livelihood [1]. Pasture-based dairy production systems are mainly found in temperate regions, where grass is the cheapest feed used in milk production [2]. Pasture grazing can be used in feeding systems for dairy cows in other parts of Europe as well, but its importance is lower [3]. It is estimated that 98% of Irish and 92% of British dairy farms operate pasture-based systems, compared to only 20% in the Czech Republic, less than 10% in Greece, and virtually none in Bulgaria [4]. Even herds with access to pasture are typically kept indoors during the winter and around calving [5].

In general, for milk production, pasture grass is a higher quality forage than grass silage [6]. In temperate regions of Europe, grass growth is highly variable [7], varying among years [8], seasons, as well as regions [9]. It depends on many factors: pasture management, the sward renewal practices used, the level of fertilization, the course of weather conditions (e.g., precipitation, temperature, solar radiation) and soil type. The nutritional value of pasture sward varies depending on the season, growth stage, and age of regrowth.

The quality of pasture grass can be optimized through rational grazing and pasture management. For example, rotation length, biomass weight before grazing [10], and sward height pre- and pos- grazing [11] can affect grass quality, as well as grass supply. A leafy sward in spring has a high nutritive value, while a sward at the reproductive stage in summer has a higher fiber content and lower digestibility [12]. The nutritional value of pasture sward also depends on their botanical composition. Swards with a significant proportion of legumes often have a higher feed value than grass-only swards ^[13][14][13,14].

Rationally used pasture provides grazing animals with high-quality roughage, containing mainly energy, protein, macro- and microelements, and vitamins ^[15][16][15,16]. In addition to valuable species of grasses and legumes, the composition of pasture sward includes dicotyledonous plants called herbs. They contain many valuable biologically active substances such as tannins, flavonoids, saponins, pectins, terpenes, alkaloids, phenols, as well as essential oils ^[17][18][17,18]. These compounds have positive effects on cattle gastrointestinal function and health (antioxidant and antiparasitic effects, enhancement of the immune system) ^[19][20][19,20], and the quality of beef and dairy products [21].

Livestock grazing influences pasture biodiversity, particularly the botanical composition of plant communities ^[22][23][24][22,23,24], as well as the quantity and quality of forage produced [25], the dynamics of sward regrowth [26], the variability of species occurrence and contribution, and the landscape that pastures create ^[27][28][27,28]. Pasture use contributes to a rich diversity and variability in the vegetation cover maintaining the maintenance of all forms of biodiversity ^[29][30][31][29,30,31]. However, the diversity of plant communities created by grazing by animals can change depending on environmental conditions, including regional climate variability [32], grazing intensity [33], and soil nutrient availability [34]. Grazing lands also provide ecosystem services including regulation and storage of water flows [35], nutrient cycling, and C sequestration ^[36][37][36,37].

The production results of grazing animals depend on the stocking method and management of grazing. In general, there are two stocking methods, i.e., rotational and continuous stocking, among which different modifications are used depending on the various factors. Farmers have different considerations when choosing a stocking methods. In their choice, they may take into account the impact of grazing on yield and forage utilization, but also many other factors such as environmental impact, animal welfare, and other aspects. In some countries, legislation is a decisive factor. Grazing methods and pasture organization should be optimally adapted to the possibilities and specific characteristics of the farm.

The cheapest stocking method for cattle, mainly used on extensive pastures, involving continuous stocking of the sward, from spring to autumn, over the entire pasture area, is free grazing. The supply of forage depends on the season, with an over-supply of forage in spring, while there can be a periodic shortage of forage in summer when rainfall is scarce. Carrying out maintenance and rational fertilization in this stocking method is very difficult. Pastures under this stocking method are prone to a more rapid degradation process, involving the disappearance of valuable grass and legumes and the development of weeds ^[38][116].

All modern intensive stocking methods use the principles of rotational stocking ^[39][117]. Rotational stocking involves the frequent movement of livestock through a series of pasture subdivisions called paddocks ^[40][118]. Rotational stocking has many potential economic and environmental advantages ^[41][42][119,120] such as increases herbage production for livestock ^[43][44][121,122] and improves animal production ^[45][123], prevents overgrazing, and reduces soil erosion ^[46][124]. Rotational stocking has been found to improve soil microbial activity ^[47][125], which may promote greater stabilization of organic matter ^[48][126]. Moreover, rotational stocking results in fewer herd health problems and many others. Jordon et al. ^[49][127] provided empirical confirmation of the mechanisms by which rotational stocking and increasing sward biodiversity through the inclusion of perennial herbaceous plants (herbaceous strips) can increase forage production and animal growth rates. However, some studies have shown that rotational stocking does not provide any unique ecological or agricultural benefits compared to continuous stocking ^[42][120]. But, more important than the stocking method is the grazing intensity which is thought to have a major impact on soil organic carbon storage and soil quality indicators in grassland agroecosystems. Moreover, soil improvement resulting from intensive rotational stocking does not occur rapidly ^[44][50][122,128]. It takes three to five years to start seeing beneficial changes in vegetation cover and soil microbial activity ^[51][129]. In general, intensive rotational stocking is more likely to be successful in areas with higher rainfall ^[52][106]. In northern Spain, where the average annual rainfall is 1000 mm, intensive rotational stocking by sheep resulted in higher forage production and increased carbon sequestration ^[53][130]. In more arid areas, intensive rotational stocking with frequent movement of animals can result in reduced weight gain ^[54][104]. Rotational stocking also has some disadvantages. It requires more fencing and labor (an effective alternative to traditional fencing is virtual fencing). It may result in soil compaction and degraded water quality if livestock is not moved regularly, as well as may increase internal parasites in irrigated rotational pastures.

To some extent similar to rotational stocking is guarded grazing, where the herd is supervised by a shepherd. This involves the animals returning after a certain period to areas previously grazed. This stocking method is practiced mainly in the mountains when grazing sheep and can be of great importance in naturally valuable areas as a factor stimulating the increase of their biodiversity and the preservation of naturally valuable areas ^[55][131].

A very efficient method of rotational stocking is tethered grazing (staking the animals). The great advantage of this method is the possibility of feeding each animal individually, easily regulating the amount of forage available to it. This stocking method is mainly used on farms with few cattle or horses. Staking causes some inconvenience due to the need to move the stakes and water the animals (bringing them to the watering hole or bringing water to the pasture). When grazing in this method, the animals have limited movement and, if left in the same place for a long time, they may eat the sward too intensively, which can cause damage by too much trampling or low biting.

Continuous stocking is the least controlled of the stocking methods. It consists of grazing the sward, over the whole or partially regulated area of the pasture, from spring to autumn in a slow method. The basis of this method is the control of the height of the grazed sward. As the sward is grazed and the rate of increase decreases, additional spare areas are incorporated into the grazing area to provide a reserve of feed for the whole herd. This method is often used by farmers with relatively large pasture areas and low numbers of livestock. Continuous stocking usually results in lower productivity per animal and lower output per unit of land. This stocking method is applied for animals that do not require high maintenance, such as sheep, dry cows, growing heifers, and low-milking cows. It requires lower amounts of labor, fencing, and water sources. The animals selectively graze the most palatable forage, which generally increases gains per animal. Selective grazing reduces total pasture productivity and leads to overgrazing in some parts of the pasture. Forage use can be improved by varying the stocking rate or temporarily fencing off part of the pasture for herbage harvest (“buffer” system).

Ultra-high Stock Density (UHSD) or commonly known as “Mob Grazing” or “Flash Grazing” is a short-duration, high-density grazing with a longer than usual grass recovery period. It has been proposed as a way to increase soil carbon storage and range quality. This system has been adopted in the USA, Canada, and the UK ^[56][132] for intensive grazing of cattle, sheep, and goats. High stocking densities result in a high fertilizing effect of the manure left on the small pasture area. The high stocking rate of the pasture means that much of the plant biomass is trampled by the hooves of the animals into the ground to form mulch that protects the soil from erosion. Plant residues and animal excreta contribute to an increase in organic matter content and improve soil nutrient abundance, which positively influences soil microorganisms and stimulates plant production ^[57][133]. However, some studies show a negative effect of mob-grazing on soil organic matter and other desirable properties of pastures ^[58][134]. According to ^[59][135], high densities of livestock increase soil C in warm-season grasses and decrease soil C in cool-season grasses. Moreover, mob-grazing can cause soil erosion by enhancing soil compaction, which has a negative impact on soil water infiltration and plant growth ^[60][61][57,136]. There is a need for a better understanding of the mechanisms by which mob-grazing may positively or negatively influence soil C storage and vegetation ^[42][120].

Adaptive Multi-Paddock (AMP) grazing has been developed as a conservation-oriented grazing management approach for improving the ecological function of grazed ecosystems by continuously adjusting the number of grazing animals and the duration of herbivory in response to changes in forage availability ^[62][63][137,138]. Multi-paddock grazing management has been recommended since the mid-20th century as an important tool to adaptively manage rangeland ecosystems to sustain productivity and improve animal management. AMP grazing employs multiple paddocks per herd to enable short grazing periods leaving sufficient post-herbivory plant residue for regrowth, and long recovery periods to accommodate seasonal variation in plant regrowth ^[64][139]. It was found that, based on restored soil health, water conservation, and improved ecosystem services, AMP grazing was superior to heavy continuous grazing ^[43][121]. Similarly, it was found by Hillenbrand et al. ^[65][140] that AMP grazing improves the forage biomass, water infiltration, and total soil carbon concerning heavy continuous grazing ^[66][60]. It was confirmed that long-term AMP grazing improves streamflow, water balances, and water quality at the ranch and watershed scales ^[67][68][69][141,142,143]. AMP grazing also increases net primary productivity, soil C and N, and reduced C losses in runoff and sediment ^[70][144].

Alternative pasture management which can be used to increase ruminant performance and reduce gastro-intestinal nematodes is mixed grazing. In Germany, sheep and goat grazing is used to rehabilitate areas over-exploited by intensive cattle grazing ^[71][145]. This is due to the different dietary preferences of the different animal species. Sheep and goats eat woody and low-value plants that are avoided by cattle. In addition, sheep are less picky about the plants growing next to the dung left by cattle, which contributes to the increased forage used. Mixed grazing, compared to grazing only one animal species, not only allows better utilization of the sward ^[72][146] but increases the biodiversity of the sward and soil bacterial flora ^[73][74][147,148], arthropods, and birds ^[75][149]. Research in Ireland on cattle and sheep herds showed that sheep follow grazing after cattle promoted a higher proportion of clover in the sward and a greater number of clover volunteers from seed not digested by cattle and sheep ^[72][146]. An additional benefit of such grazing is less sward damage, reduced invasion by animal parasites and the emergence of more beneficial plant-pollinating insects ^[76][150].

The silvopastoral grazing system (SPS) involves grazing animals in wooded areas, traditional orchards, and groves (Figure 1). It is a system of short rotation of animals staying in tree-lined pastures. This system is commonly found throughout the world. Trees and bushy vegetation provide shelter for the animals, but can also provide food ^[77][151]. Husak and Grado ^[78][152] found that this grazing system contributes to sustainable livestock production and increases the productivity, profitability, and viability of area use. There is considerable evidence that SPS can increase production efficiency, increase carbon sequestration, and improve N cycling on land used for livestock production ^[79][153]. Other advantages of this system are the restoration of uncultivated land to agricultural production, low labor inputs compared to intensive production, improved welfare of beef cattle (minimal stress on the animals), and high-quality beef sold as an organic product. This is supported by a study by Skonieski et al. ^[80][154], according to which the SPS improved the welfare of grazing Jersey cows, as evidenced by an improved physiological response to heat stress, increased grazing time, and reduced standing time (resting + ruminating) compared to cows grazing on conventional pasture.

Sometimes, innovative producers are grazing sheep in the areas occupied by farms with solar PV panels. These surfaces also need tending, mowing, and biomass removal, so sheep and goats are increasingly being used for this purpose. Grazing sheep under such panels is possible without special modifications to the photovoltaic installations. Grazing cattle under solar panels requires stronger support poles and panels installed higher off the ground ^[81][82][155,156].

In addition to the advantages of pasture feeding, related to the possibility for cattle to consume good quality roughage, the positive impact on animal welfare, and the higher quality of animal products, there are unfortunately also some disadvantages. Pasture feeding is undoubtedly more time-consuming and labor-intensive in some respects (animal monitoring and grazing management) compared to keeping cattle in alcove systems. Grazing animals on pastures also entails costs related to the purchase and installation of structural elements for pasture fencing ^[83][45]. But undoubtedly grazing is the cheaper way to feed domestic herbivores, and structures to maintain animals indoors have a higher cost than to maintain in pastures even with different paddocks.

2.2.1. Virtual Fencing

In countries where the pasture feeding system is well developed, virtual pasture fences are used, delimiting the area to be grazed. When the animal approaches the virtual zone, it is given an audible signal, which tells it to stop. The farmer remotely—in the office, at the computer—determines the area to be grazed, over which the cows move independently ^[84][157]. Virtual fencing devices use an algorithm that combines GPS animal positioning with animal behavior to implement the virtual fence ^[85][86][158,159]. Like conventional fencing, virtual fencing is used to provide a boundary to the grazing area to deter animals from moving further, but unlike conventional fencing, it does not create a physical barrier ^[87][160]. With a virtual fence system, animals learn a virtual barrier not to cross by associating a sound stimulus with an electrical stimulus. When approaching the fence boundary, a warning acoustic signal is triggered and the electrical impulse stimulus from the collar is only produced as a punishment if the animal continues to move forward. If the animal turns away or stops at the audible signal, the electrical impulse stimulus is not initiated by the collar. Cattle have been shown to learn this association easily in several trials; however, there is a high variability in learning and behavioral responses between individuals ^[88][89][90][161,162,163]. Virtual fencing is highly useful and has great potential for controlling sheep distribution during grazing, but the development of virtual fencing technology for sheep grazing is still less advanced than for cattle ^{[91][92][93][94]}[164,165,166,167].

2.2.2. Automation of Fences in Pastures

Automatic gates on individual plots can be used to control individual groups of cows divided by yield to grant them access to different areas of pasture with different yields. Control can be implemented by programming the time the animals are in the quarters or by individual remote control by the farmer. The gate system can be combined with an AMS automatic milking system ^[95][96][168,169]. GPS-guided mobile fences are also used, which make a new area of pasture with fresh feed available every pre-programmed time for the grazing cattle herd ^[97][41]. Currently, for the most part, the organization of grazing and control of the allocation of plots is limited to the labor-intensive and less efficient conventional fencing system ^[98][170].

2.2.3. State-of-the-Art Applications and Programmes to Predict Pasture Yields

A new feature is the automatic mowing of the pasture underplanting immediately after the cows have grazed on the plot. There are also more and more computer programmes available to assist the farmer in grazing management, making it possible to predict the start of grazing a month in advance based on the current and predicted weather situation. This allows planning when and for how long the animals will be grazed ^[97][41].

2.2.4. Automatic Milking System (AMS) at Pasture

On farms where a pasture-based feeding system is used, automatic milking machines are often used for milking. The integration of automatic milking systems (AMS) into pasture-based cattle farming poses new challenges that are very different from those already known in systems where cows are grown in cowsheds. A particular challenge is the grazing of large cattle herds, where more than 50% of the total diet is pasture forage. When an automatic milking system (AMS) is used, animals have to travel considerable distances from the pasture to the milking point ^[99][171]. Information reported by Islam et al. ^[100][172] shows that cows milked by automatic milking machines had to travel distances exceeding 1.0 km on average, in cases where the farm size was more than 80 ha. Significant distances between the grazing area and the location of the automatic milking machine result in longer intervals between milkings and are associated with increased energy loss by the animals spent on constant movement ^[101][102][173,174]. In addition to the positive sides, frequent movement can also have negative effects on animal welfare. Travelling long distances increases cortisol levels (an indicator of stress) and can cause gait disturbances or lameness or cause mechanical injuries to the hoof ^[103][175].

2.3. Innovations to Improve Feed Quality

2.3.1. Temporary Pastures

The grazing of animals can be carried out not only on permanent grassland but also on temporary pastures. They occupy the soil for one to five years and are made up of graminaceous plants or grasses mixed with legumes and other species. The most common species in this type of pasture include grasses: Agrostis spp., Festuca pratensis, Lolium perenne, and Dactylis glomerata. Recently, ryegrass varieties with high growth vigor and high sugar content have been used in temporary grassland swards. The legumes (Trifolium repens, Lotus spp., and Medicago sativa) are rich in protein and can help fix atmospheric nitrogen in soils ^[104][105][195,196]. Green fodder from such pastures, due to the high proportion of valuable grasses and legume species, has a higher protein and sugar content and better digestibility ^[106][197]. Temporary pastures are usually used for intensive grazing or grazing with a ration of supplementary roughage. Incorporating temporary pastures into the crop rotation cycle can help increase yields in the short term. It can also change the level and/or quality of soil organic matter and, in the medium term, affect the biological properties of the soil ^[107][198].

2.3.2. Multi-Species Pastures MSP

The improvement of degraded pastures is important for increasing pasture herbage yield and animal production. For pasture establishment and renovation, seed mixtures composed of different grass species or grasses with legumes are almost exclusively used, which guarantees the production of large quantities of good quality animal feed ^[108][199]. A new aspect in grassland forage production is the addition of herbaceous species naturally occurring in grassland communities to seed mixtures, to obtain multi-species pastures MSP or mixed-herb leys ^[109][110][200,201]. The addition of herbs improves the nutritional value of the pasture sward while maintaining a high and stable yield. Cichorium intybus (L.), Plantago lanceolata (L.) and Achillea millefolium (L.) increase the mineral content, resulting in a better-balanced ratio, improving the animal condition and growth. A well-balanced diet containing herbs in its composition, when used in calves, can influence the subsequent production performance of adult animals ^[111][112][202,203]. Herbs improve the palatability of feed, stimulate digestive processes, and increase the feed intake of animals. Palatability-enhancing species include Carum carvi (L.), Sanguisorba officinalis (L.), Daucus carota (L.), Pastinaca sativa (L.), Rumex acetosa (L.), and Salvia officinalis (L.). The herbs contain specific biologically active substances of tannins, saponins, terpenes, flavonoids, and alkaloids, which can have a positive impact on animal health prevention ^[113][204]. Essential oils found in herbs increase palatability and influence the feed intake of animals [18]. Terpenes, flavonoids, and alkaloids have positive effects on cattle gastrointestinal function and health by enhancing the immune system, and antioxidant and antiparasitic effects in the gut ^[49][127]. Lambs grazed on pastures containing C. intybus showed less infestation with internal parasites and the animals had higher growth rates than animals grazed on pastures without herbs ^[114][205]. Carum carvi (L.), Anethum graveolens (L.), and Artemisia vulgaris (L.) have similar effects. These herbs contain tannin compounds and bitters that reduce the incidence of gastrointestinal parasites and also have antidiarrheal effects ^[115][206]. A diarrheic effect has been observed when plants such as Pimpinella anisum (L.), Lotus uliginosus (Schkuhr), and Anthriscus cerefolium (L. Hoffm.) are ingested. The correct percentage of herbs in the feed is important. Through a meta-regression, McCarthy et al. ^[116][207] investigated whether there is an optimum inclusion percentage of herb species in a grazing sward to increase milk yield. However, despite a positive relationship between herb percentage in the sward and milk yield, the association between herb percentage and milk yield was non-significant. The authors concluded that continued research investigating management strategies for multispecies swards is needed to determine optimum grazing strategies for multispecies swards in modern pasture-based dairy systems. An optimally composed multispecies mixture containing herbs in its composition under stress conditions, e.g., drought, can provide a sward yield comparable to a mixture containing only grasses and legumes ^[117][208]. Increasing pasture biodiversity through the use of multi-species seed mixtures also has a positive impact on environmental aspects. The deep root system of Cichorium intybus (L.) contributes to the utilization of mineral nitrogen from deeper subsoil layers, which is not available in the root system of grasses ^[118][209].