In tropical grasslands, moderate grazing led to soil carbon storage and resulted in greater productivity and soil water-holding capacity, potentially enhancing grassland resilience to climate change . Mixed grazing of different livestock species at moderate levels promoted higher diversity and ecosystem multi-functionality . Soussana et al. , who accounted for greenhouse gas budgets at nine European grassland sites, found that grasslands have the potential to offset a significant proportion of global emissions of greenhouse gases as a result of livestock grazing. These findings have significant implications for achieving carbon neutrality and carbon peaking. Altogether, integrating grassland grazing into existing livestock farming systems in China will undoubtedly meet the increasing human demand for high-quality foods and valuable ecosystem services.Despite the potential positive contributions to humans, grassland-based ruminant farming systems in China still face severe problems, such as low production output , greenhouse gas emissions caused by ruminants due to low-quality forage feeding , and grassland degradation caused by overgrazing . We determined that the key reason for the emergence of these problems lies in the lack of knowledge and techniques for integration of nutrition manipulation and grazing manipulation. In grassland grazing systems, herbivore foraging behaviors are a central feature in the animaleplant interface . Herbivore foraging selection can directly influence plant community composition and diversity by changing competition among plants, affecting grassland ecological processes and ecosystem functions. Simultaneously, foraging selections of livestock under grazing conditions directly determine the nutrient supply resulting from grazing and forage resources, hydroponic dutch buckets which are essential for nutrition management decisions.
Therefore, accurately determining the diet selection of grazing ruminants relative to available herbage is necessary for future developments of these techniques. However, complex variables create significant challenges for accurately predicting the foraging selection behaviors of ruminants under grazing conditions, making predictions extremely difficult. The challenges we explore are not exhaustive but are focused on key factors in developing sustainable grassland-based ruminant farming systems.Animals may selectively adjust their dietary composition according to their individual experiences, nutritional status, and physiological status. Previous studies have shown that ruminants tend to choose specific plants and plant parts when grazing . Decisions about what to eat are based on expected rewards and previous experiences, affecting an animal’s food preferences . In utero and early life experiences of livestock may alter food preferences through elusive epigenetic effects that drive the voluntary forage intake of animals later in life . For instance, Chadwick et al. found that lambs exposed to salt bush in utero grew faster and handled greater salt loads than lambs born from ewes grazed on mono-cultures of introduced grasses. Wiedmeier et al. demonstrated that cattle exposed to high-fiber forages early in life showed higher nitrogen retention and greater abilities to digest fiber during adulthood than cattle reared on low-fiber diets. Available evidence has also suggested that ruminants selectively balance their diet according to their nutritional requirements. For instance, grazing ruminants maximize their energy intake through selective feeding on forages, during a day , or within a specific feeding schedule . Mineral-deficient cattle and sheep have been observed eating soil, licking urine patches, eating fecal matter, or eating dead rabbits, whereas animals without mineral deficiencies may sniff or lick these items but rarely consume them . Furthermore, ruminants may selectively feed based on their satiety and changing physiological needs, such as growth, lactation, pregnancy, parturition, and weaning .
Herbivores selectively consume individual plants based on their chemical composition, determined by secondary compounds, nutritional ingredients, and flavor substances. Typically, herbivores prefer to feed on plants containing only modest amounts of secondary metabolites. In small quantities, these compounds reduce bloating and improve protein utilization, immune responses, resistance to gastrointestinal nematodes, and reproductive efficiency . However, excessive volumes of secondary metabolites in grassland plant species limit the forage chosen for ingestion by grazing livestock. For example, goats selectively reduce their intake of forages with a greater composition of secondary compounds such as tannins . Lambs choose to reduce meal size and increase meal intervals when their diet is high in terpenes . Animals generally forage based on flavor profiles and nutrient content, especially when consuming different components of available plant anatomy . The spatial distribution of plant populations, plant species richness, and spatial relationships among different plant species in natural grasslands affect livestock foraging behaviors. Specifically, sheep increased consumption of high-preference species when low-preference species followed a clumped distribution rather than a random distribution . High plant species richness enhanced the frequency that animals switched diets and weakened the ability of herbivores to choose food, increasing foraging costs and interfering with the herbivore’s choice of foraging . Herbivores consumed the largest number of palatable plants when 3 plants species were segregated into 3 patches independent of each other. In contrast, the total forage intake of herbivores for all plant species was reduced when the 3 species were homogenously distributed through patches in a spatially equal neighbor relationship .
Local environments can influence dietary selections by grazing livestock. Extensive studies with pen-fed ruminants have shown that the ambient temperature affects feeding willingness ; however, very little empirical data is available describing the mechanisms affecting herbage intake in grazing ruminants under variable temperature management. Nonetheless, the physiological consequences of heat or cold stress may be similar for ruminants under housing or grazing. In beef cattle, feed intake increased at temperatures from 15 to 28 C but decreased at temperatures above 28 C . For grazing ruminants, behavioral responses amplified the effects of temperature stress on herbage intake under heat and cold stress . Studies examining the relationship between temperature stress and foraging willingness have primarily exhibited inconsistent results. Adams et al. observed significant reductions in the herbage intake of grazing cattle under acute cold stress, whereas Beverlin et al. found only minor changes in herbage intake for cows experiencing changing temperatures . Due to the inconsistent results, whether or not temperature stress affects forage intake in grazing ruminants remains ambiguous. The most relevant measurements to date are also relatively short-term, making it difficult to make recommendations on adjusting intake predictions. The effects of ambient temperature on forage intake may also be amplified by other environmental factors, like wind or precipitation conditions. For instance, wind velocity exacerbated the effects of low temperatures on grazing ruminants during winter but could help alleviate heat stress in summer . Previous studies also reported that rainfall events temporarily reduced the intake of grazing cattle by 10% to 30%, decreasing the cattle’s average daily gain . In addition, terrain plays a principal role in the forage selection of grazing livestock . When examining geographic and environmental factors affecting livestock feeding behaviors, cattle tended to avoid foraging on pastures with slopes greater than 10% inclines during grazing trials, and the number of grazing animals decreased as the slope increased. On slopes with a greater than 60% incline, almost no animals were found foraging . The location of water sources and social behaviors also affected foraging selection by grazing livestock .In addition to variable environmental factors, grazing regimes established by managers are also vital components of estimating forage intake in grazing animals.
Kitessa and Nicol found that cattle continuously co-grazed with sheep showed a lower herbage intake than those rotationally co-grazed with sheep. Perez-Ramirez et al. demonstrated that decreased grazing time of dairy cows strongly increased the pasture intake rate and decreased the foraging selectivity relative to available herbage. Congruently, dairy cows were more motivated to forage when receiving a low-supplement feeding regime. Furthermore, Savian et al. found that the sheep undergoing rotatinuous stocking exhibited an increase in daily herbage intake and improved bite rates compared to those under traditional rational stocking management, suggesting that rotatinuous stocking maximized the herbage intake and optimized the grazing time of sheep. Nevertheless, the factors influencing livestock dietary selections are also constantly changing ,bato bucket as grazing animals are foraging in a dynamic world. Herbage production, grassland community composition, and plant chemical composition fluctuate considerably in response to changing environmental and climatic conditions . This perspective has been supported by a longitudinal study of arid rangelands . Over the 37-year study period, herbage production varied annually between 4% and 307% of the median value. Simultaneously, temporalespatial variations in the herbage’s chemical composition, richness, evenness, and biomass led to heterogeneity. As a result of grazing, preferred plants and specific parts of the plant’s anatomy are removed from the landscape over time, leading to continuous changes in the plant community composition within pasture environments . The complex influencing factors, combined with continuously changing grassland herbage resources , make foraging selections of grazing ruminants extraordinarily complex and unpredictable.In the future, continued research is necessary to clarify and explore the mechanisms underlying foraging behavior, thereby helping us better predict grazing ruminants’ diet selection. Farmers, landowners, and livestock managers have an obligation to embrace vital agricultural and technological advances and establish new nutritional assessment methods for grazing ruminants. Implementation of nutritional intake assessments based on foraging selection behaviors assessment will allow stabilization and increased production in livestock agribusiness. Consequently, our knowledge regarding the nutritional requirements of grazing ruminants requires greater refinement. Many additional elements have been identified to affect the nutritional requirements of grazed ruminants , so knowledge gleaned from animals kept indoors cannot be extrapolated to ruminants in outdoor pasture environments. Further data collection and longitudinal studies are necessary to build mechanistic models of the nutritional requirements of grazing ruminants in terms of energy, protein, minerals, vitamins, and water. Continued research should focus on the critical factors controlling grassland ecological and productive functions.
Biodiversity has been identified as the primary determinant of grassland ecosystem services and functions . Experimental studies have shown that the stability and functionality of grassland ecosystems require high plant species diversity and multi-trophic species diversity for co-regulation like that of below ground soil microbial diversity and above ground community diversity . Improving grassland biodiversity by systematically managing grazing practices is critical for grassland ecological service advancement. Therefore, future studies should target identifying mechanisms of grassland biodiversity maintenance and grazing regulations on grassland biodiversity, offering a scientifically reproducible basis for guiding grazing manipulation practices . It has long been recognized within livestock production practices that rumen microbial communities play an essential role in improving ruminant production and health. The rumen microbiome, consisting of bacteria, protozoa, fungi, archaea, and viruses, composes a sophisticated symbiotic network essential to the maintenance, immune function, and overall production efficiency of the host ruminants . Digestion performed by the rumen microbial community accounts for up to 70% of the total dietary energy in ruminants. The symbiotic metabolic operation between a ruminant host and the rumen microbiome results in many end products critical to other biological processes, including developing the rumen epithelium and establishing the immune system . Ergo, improving our understanding of rumen microbial ecology in grazing ruminants promotes enhanced animal production efficiencies. Considering nutritional manipulation for grazing livestock should also be a management option to optimize rumen microbial communities. Ultimately, this in-depth examination of livestock grazing management and nutritional practices aims to provide a blueprint for developing sustainable, grassland-based ruminant farming systems by integrating animal behavior analysis, animal nutrition principles, and grassland ecology, to achieve “winewin” outcomes for grassland ecological/ecosystem functions and livestock production policies .