Livestock production system management responses to thermal challenges

The adaptive capabilities of animals and livestock production systems have been emphasized in this report. Biometeorology has a key role in rational management to meet the challenges of thermal environments. While the focus is primarily on cattle in warm or hot climates, the importance of dynamic animal responses to environmental challenges applies to all species and climates. Methods used to mitigate environmental challenges focus on heat loss/heat production balance. Under cold stress, reduction of heat loss is the key. Under heat stress, reduction of heat load or increasing heat loss are the primary management tools, although heat-tolerant animals are also available. In general, livestock with health problems and the most productive animals (e.g., highest growth rate or milk production) are at greatest risk of heat stress, thereby requiring the most attention. Risk management, by considering perceived thermal challenges, then assessing the potential consequences and acting accordingly, will reduce the impact of such challenges. Appropriate actions include: shade, sprinkling, air movement, or active cooling. Summarizing, the most important element of proactive environmental management to reduce risk is preparation: be informed, develop a strategic plan, observe and recognize animals in distress, and take appropriate tactical action.     

Adaptation to hot climate and strategies to alleviate heat stress in livestock production

Despite many challenges faced by animal producers, including environmental problems, diseases, economic pressure, and feed availability, it is still predicted that animal production in developing countries will continue to sustain the future growth of the world's meat production. In these areas, livestock performance is generally lower than those obtained in Western Europe and North America. Although many factors can be involved, climatic factors are among the first and crucial limiting factors of the development of animal production in warm regions. In addition, global warming will further accentuate heat stress-related problems. The objective of this paper was to review the effective strategies to alleviate heat stress in the context of tropical livestock production systems. These strategies can be classified into three groups: those increasing feed intake or decreasing metabolic heat production, those enhancing heat-loss capacities, and those involving genetic selection for heat tolerance. Under heat stress, improved production should be possible through modifications of diet composition that either promotes a higher intake or compensates the low feed consumption. In addition, altering feeding management such as a change in feeding time and/or frequency, are efficient tools to avoid excessive heat load and improve survival rate, especially in poultry. Methods to enhance heat exchange between the environment and the animal and those changing the environment to prevent or limit heat stress can be used to improve performance under hot climatic conditions. Although differences in thermal tolerance exist between livestock species (ruminants > monogastrics), there are also large differences between breeds of a species and within each breed. Consequently, the opportunity may exist to improve thermal tolerance of the animals using genetic tools. However, further research is required to quantify the genetic antagonism between adaptation and production traits to evaluate the potential selection response. With the development of molecular biotechnologies, new opportunities are available to characterize gene expression and identify key cellular responses to heat stress. These new tools will enable scientists to improve the accuracy and the efficiency of selection for heat tolerance. Epigenetic regulation of gene expression and thermal imprinting of the genome could also be an efficient method to improve thermal tolerance. Such techniques (e.g. perinatal heat acclimation) are currently being experimented in chicken.     

A generalised additive model to characterise dairy cows’ responses to heat stress

Heat stress is one of the most critical issues jeopardising animal welfare and productivity during the warm season in dairy cattle farms. The global trend of increase in average and peak temperatures is making the problem more and more serious. Many devices have been introduced in livestock farms to monitor and control temperature-humidity index, as well as animal behaviour and production parameters. The consequent availability of collected databases has increasingly enhanced the research aimed to understand the consequences of heat stress in cattle, in relation to genetic, reproductive, productive and behavioural features. Moreover, these investigations laid the foundations for the development, calibration, validation and test of numerical models quantifying the individual responses to heat stress conditions. In this work, a generalised additive model with mixed effects has been developed to analyse the relationship between milk production, animal behaviour and environmental parameters based on data surveyed in 2016 in an Italian dairy farm. Each cow has been characterised in terms of her response to heat conditions, and the results led to define three classes of susceptibility to heat stress within the herd. These attributes have then been related to the various phenotypic parameters collected by the precision livestock farming devices used in the farm. The study provides a model to understand the effects of heat stress conditions on individual animals in relation to the main parameters describing their rearing conditions; moreover, the results contribute to improve the herd management by lending indications to define targeted treatments according to the cow’s characteristics.     

Dynamic changes in blood immune cell composition and function in Holstein and Jersey steers in response to heat stress

Heat stress has detrimental effects on livestock via diverse immune and physiological changes; heat-stressed animals are rendered susceptible to diverse diseases. However, there is relatively little information available regarding the altered immune responses of domestic animals in heat stress environments, particularly in cattle steers. This study aimed to determine the changes in the immune responses of Holstein and Jersey steers under heat stress. We assessed blood immune cells and their functions in the steers of two breeds under normal and heat stress conditions and found that immune cell proportions and functions were altered in response to different environmental conditions. Heat stress notably reduced the proportions of CD21⁺MHCII⁺ B cell populations in both breeds. We also observed breed-specific differences. Under heat stress, in Holstein steers, the expression of myeloperoxidase was reduced in the polymorphonuclear cells, whereas heat stress reduced the WC1⁺ γδ T cell populations in Jersey steers. Breed-specific changes were also detected based on gene expression. In response to heat stress, the expression of IL-10 and IL-17A increased in Holstein steers alone, whereas that of IL-6 increased in Jersey steers. Moreover, the mRNA expression pattern of heat shock protein genes such as Hsp70 and Hsp90 was significantly increased in only Holstein steers. Collectively, these results indicate that altered blood immunological profiles may provide a potential explanation for the enhanced susceptibility of heat-stressed steers to disease. The findings of this study provide important information that will contribute to developing new strategies to alleviate the detrimental effects of heat stress on steers.     

Melatonin, an underestimated natural substance with great potential for agricultural application

Melatonin (MEL) was thought to be only a neurotransmitter found in vertebrates until its detection in other organisms including plants. Although the number of publications on MEL function in plants is expanding, the knowledge of this subject is still insufficient. Among many functions which MEL performs in plants, its role as an antioxidant and a growth promoter is most supported by experimental evidence. This compound is an independent plant growth regulator and it may mediate the activities of other plant growth regulators. Due to its antioxidant properties MEL may also stabilize cell redox status and protect tissues against reactive oxygen and nitrogen species which accumulated under stressful environment. Some researchers propose that MEL could be used to improve the phytoremediation efficiency of plants against different pollutants. In this paper we show that exogenous MEL applied into the seeds could be a good biostimulator improving not only seed germination, seedling/plant growth but also crop production especially under stress conditions. We also believe that this compound can increase food quality (the aspect of functional food) and may improve human health. Since MEL is inexpensive and safe for animals and humans its application as a biostimulator could be a good, feasible and cost-effective method useful in agriculture.     

Stress biomarkers and proteomics alteration to thermal stress in ruminants: A review

Heat stress may adversely affect physiochemical and immune responses of livestock and alter biological functions. The comfort or thermoneutral zone for livestock, which has long been a subject of research, mainly depends on species, breed, and health. Heat stress is associated with impaired livestock productivity due to reductions in feed intake, growth rates and immunity and changes in blood constituents and biological pathways. In ruminants, elevated temperatures have deleterious consequences on protein synthesis. Exposure of ruminant animals to elevated temperatures may induce release of heat shock proteins (HSPs); HSPs usually enter the blood circulation during tissue damage and causes cell necrosis or death. Additionally, hyperthermia is associated with augmented production of cellular reactive oxygen species (ROS), which cause protein degradation and further decrease protein synthesis by preventing protein translation. Moreover, it has been suggested that high environmental temperatures lead to increased inflammatory signalling in tissues via activation of the nuclear factor kappa B (NF-κB) and tumor necrosis factor alpha (TNF-α) pathways as well as via alteration of skin colour gene (melanocortin 1 receptor (MC1R) and premelanosome protein (PMEL)) expression. Previous proteomics analyses have suggested that heat stress can reduce adenosine triphosphate (ATP) synthesis, alter gluconeogenesis precursor supply, and induce lipid accumulation in the liver with subsequent disturbance of liver structure. This review focuses on the scientific evidence regarding the impact of heat stress on immune and inflammatory responses, antioxidant status, stress biomarkers, skin colour gene (PMEL and MC1R) expression and proteomic profiles in ruminants.     

抗热应激添加剂对奶牛产奶量、生理及血液指标的影响

为研制一种有效的奶牛抗热应激添加剂,将50头健康荷斯坦奶牛随机分为5组,对照组饲喂基础日粮,4个试验组饲喂基础日粮添加不同抗热应激添加剂,连续饲喂30d,测定产奶量、生理及血液指标。结果显示：中草药组、中草药＋纤维素酶组、中草药＋缓冲盐组、中草药＋缓冲盐＋纤维素酶组比对照组产奶量分别提高24．8％、27．9％、37．2％、39．5％;中草药剂和缓冲盐可减缓热应激奶牛的体温（P〉0．05）、呼吸和心率（P〈0．05）的升高,缓解外周血中自细胞数（WBC）、淋巴细胞数（LYM）、单核细胞数（MXD）、淋巴细胞百分比（LYM％）和单核细胞百分比（MXD％）（P〈0．05）的变化;添加中草药剂组肾上腺皮质醇（Cort）、促肾上腺皮质激素（ACTH）、三碘甲状腺原氨酸（T3）和甲状腺素（T4）水平基本稳定（P〉0．05）;使用中草药添加剂组谷胱甘肽过氧化物酶（GSH—Px）活性比对照组下降较慢（P〈0．05）,添加中草药加缓冲盐组GSH—Px活性可基本保持稳定（P〉0．05）。试验表明中草药剂可明显增强奶牛抗热应激力,和瘤胃缓冲盐同用效果更好,和纤维素酶同用作用不明显。     

Transgenic technology and applications in swine.

The introduction of foreign DNA into the genome of livestock and its stable integration into the germ line has been a major technical advance in agriculture. Production of transgenic livestock provides a method to rapidly introduce "new" genes into cattle, swine, sheep and goats without crossbreeding. It is a more extreme methodology, but in essence, not really different from crossbreeding or genetic selection in its result. Several recent developments will profoundly impact the use of transgenic technology in livestock production. These developments are: 1) the ability to isolate and maintain in vitro embryonic stem (ES) cells from preimplantation embryos, embryonic germ (EG) and somatic cells from fetuses; and somatic cells from adults, and 2) the ability to use these embryonic and somatic cells as nuclei donors in nuclear transfer or "cloning" strategies. Cell based (ES, EG, and somatic cells) strategies have several distinct advantages for use in the production of transgenic livestock that cannot be attained using pronuclear injection of DNA. There are many potential applications of transgenic methodology to develop new and improved strains of livestock. Practical applications of transgenesis in livestock production include enhanced prolificacy and reproductive performance, increased feed utilization and growth rate, improved carcass composition, improved milk production and/or composition and increased disease resistance. Development of transgenic farm animals will allow more flexibility in direct genetic manipulation of livestock.     

Breeding for robustness: the role of cortisol

Robustness in farm animals was defined by Knap as 'the ability to combine a high production potential with resilience to stressors, allowing for unproblematic expression of a high production potential in a wide variety of environmental conditions'. The importance of robustness-related traits in breeding objectives is progressively increasing towards the production of animals with a high production level in a wide range of climatic conditions and production systems, together with a high level of animal welfare. Current strategies to increase robustness include selection for 'functional traits', such as skeletal and cardiovascular integrity, disease resistance and mortality in various stages. It is also possible to use global evaluation of sensitivity to the environment (e.g. reaction norm analysis or canalization), but these techniques are difficult to implement in practice. The hypothalamic-pituitary-adrenocortical (HPA) axis is the most important stress-responsive neuroendocrine system. Cortisol (or corticosterone) released by the adrenal cortices exerts a large range of effects on metabolism, the immune system, inflammatory processes and brain function, for example. Large individual variations have been described in the HPA axis activity with important physiopathological consequences. In terms of animal production, higher cortisol levels have negative effects on growth rate and feed efficiency and increase the fat/lean ratio of carcasses. On the contrary, cortisol has positive effects on traits related to robustness and adaptation. For instance, newborn survival was shown to be directly related to plasma cortisol levels at birth, resistance to bacteria and parasites are increased in animals selected for a higher HPA axis response to stress, and tolerance to heat stress is better in those animals that are able to mount a strong stress response. Intense selection for lean tissue growth during the last decades has concomitantly reduced cortisol production, which may be responsible for the negative effects of selection on piglet survival. One strategy to improve robustness is to select animals with higher HPA axis activity. Several sources of genetic polymorphism have been described in the HPA axis. Hormone production by the adrenal cortices under stimulation by adrenocorticotropin hormone is a major source of individual differences. Several candidate genes have been identified by genomic studies and are currently under investigation. Bioavailability of hormones as well as receptor and post-receptor mechanisms are also subject to individual variation. Integration of these different sources of genetic variability will allow the development of a model for marker-assisted selection to improve animal robustness without negative side effects on production traits.     

Integrated models of livestock systems for climate change studies. 2. Intensive systems

The potential impact of climate change by the year 2050 on intensive livestock systems in Britain is assessed through the use of simulation models of farming systems. The submodels comprise livestock feeding, livestock thermal balance and the thermal balance of controlled environment buildings and a stochastic weather generator. These are integrated to form system models for growing pigs and broiler chickens. They are applied to scenarios typical of SE England, which is the warmest region of the country and represents the worst case. For both species the frequency of severe heat stress is substantially increased, with a consequent risk of mortality. To offset this, it would be necessary to reduce stocking densities considerably, or to invest in improved ventilation or cooling equipment. Other effects on production are likely to be small.     

Adverse impact of heat stress on embryo production: causes and strategies for mitigation

The production of embryos by superovulation is often reduced in periods of heat stress. The associated reduction in the number of transferable embryos is due to reduced superovulatory response, lower fertilization rate, and reduced embryo quality. There are also reports that success of in vitro fertilization procedures is reduced during warm periods of the year. Heat stress can compromise the reproductive events required for embryo production by decreasing expression of estrus behavior, altering follicular development, compromising oocyte competence, and inhibiting embryonic development. While preventing effects of heat stress can be difficult, several strategies exist to improve embryo production during heat stress. Among these strategies are changing animal housing to reduce the magnitude of heat stress, utilization of cows with increased resistance to heat stress (i.e., cows with lower milk yield or from thermally-adapted breeds), and manipulation of physiological and cellular function to overcome deleterious consequences of heat stress. Effects of heat stress on estrus behavior can be mitigated by use of estrus detection aids or utilization of ovulation synchronization treatments to allow timed embryo transfer. There is some evidence that embryonic survival can be improved by antioxidant administration and that pharmacological treatments can be developed that reduce the degree of hyperthermia experienced by cows exposed to heat stress.     

Book of Abstracts

A widespread occurrence of melatonin (MEL) in plant kingdom has been reported. MEL is a highly conserved molecule occurring in evolutionary distant organisms. Its role in plants seems to be similar to that in animals. Although MEL function in plants is not well known, yet a hypothesis can be put forward that it probably functions as a night signal, coordinating responses to diurnal and photoperiodic environmental cues. It has also been suggested that MEL is an independent plant growth regulator, probably its action is analogous to IAA and it may mediate the actions of other plant growth regulators. Due to its antioxidant properties MEL may also stabilize cell red-ox status and protect them against reactive oxygen species (ROS) and other harmful environmental influence.     

Aspirin-induced heat stress resistance in chicken myocardial cells can be suppressed by BAPTA-AM in vitro

Our recent studies have displayed the protective functions of aspirin against heat stress (HS) in chicken myocardial cells, and it may be associated with heat shock proteins (HSPs). In this study, we further investigated the potential role of HSPs in the aspirin-induced heat stress resistance. Four of the most important HSPs including HspB1 (Hsp27), Hsp60, Hsp70, and Hsp90 were induced by aspirin pretreatment and were suppressed by BAPTA-AM. When HSPs were induced by aspirin, much slighter HS injury was detected. But more serious damages were observed when HSPs were suppressed by BAPTA-AM than those cells exposed to HS without BAPTA-AM, even the myocardial cells have been treated with aspirin in prior. Comparing to other HSPs, HspB1 presented the largest increase after aspirin treatments, 86-fold higher than the baseline (the level before HS). These findings suggested that multiple HSPs participated in aspirin’s anti-heat stress function but HspB1 may contribute the most. Interestingly, during the experiments, we also found that apoptosis rate as well as the oxidative stress indicators (T-SOD and MDA) was not consistently responding to heat stress injury as expected. By selecting from a series of candidates, myocardial cell damage-related enzymes (CK-MB and LDH), cytopathological tests, and necrosis rate (measured by flow cytometry assays) are believed to be reliable indicators to evaluate heat stress injury in chicken’s myocardial cells and they will be used in our further investigations.     

Metabolic and hormonal acclimation to heat stress in domesticated ruminants

Environmentally induced periods of heat stress decrease productivity with devastating economic consequences to global animal agriculture. Heat stress can be defined as a physiological condition when the core body temperature of a given species exceeds its range specified for normal activity, which results from a total heat load (internal production and environment) exceeding the capacity for heat dissipation and this prompts physiological and behavioral responses to reduce the strain. The ability of ruminants to regulate body temperature is species- and breed-dependent. Dairy breeds are typically more sensitive to heat stress than meat breeds, and higher-producing animals are more susceptible to heat stress because they generate more metabolic heat. During heat stress, ruminants, like other homeothermic animals, increase avenues of heat loss and reduce heat production in an attempt to maintain euthermia. The immediate responses to heat load are increased respiration rates, decreased feed intake and increased water intake. Acclimatization is a process by which animals adapt to environmental conditions and engage behavioral, hormonal and metabolic changes that are characteristics of either acclimatory homeostasis or homeorhetic mechanisms used by the animals to survive in a new 'physiological state'. For example, alterations in the hormonal profile are mainly characterized by a decline and increase in anabolic and catabolic hormones, respectively. The response to heat load and the heat-induced change in homeorhetic modifiers alters post-absorptive energy, lipid and protein metabolism, impairs liver function, causes oxidative stress, jeopardizes the immune response and decreases reproductive performance. These physiological modifications alter nutrient partitioning and may prevent heat-stressed lactating cows from recruiting glucose-sparing mechanisms (despite the reduced nutrient intake). This might explain, in large part, why decreased feed intake only accounts for a minor portion of the reduced milk yield from environmentally induced hyperthermic cows. How these metabolic changes are initiated and regulated is not known. It also remains unclear how these changes differ between short-term v. long-term heat acclimation to impact animal productivity and well-being. A better understanding of the adaptations enlisted by ruminants during heat stress is necessary to enhance the likelihood of developing strategies to simultaneously improve heat tolerance and increase productivity.     

Future consequences and challenges for dairy cow production systems arising from climate change in Central Europe – a review

It is well documented that global warming is unequivocal. Dairy production systems are considered as important sources of greenhouse gas emissions; however, little is known about the sensitivity and vulnerability of these production systems themselves to climate warming. This review brings different aspects of dairy cow production in Central Europe into focus, with a holistic approach to emphasize potential future consequences and challenges arising from climate change. With the current understanding of the effects of climate change, it is expected that yield of forage per hectare will be influenced positively, whereas quality will mainly depend on water availability and soil characteristics. Thus, the botanical composition of future grassland should include species that are able to withstand the changing conditions (e.g. lucerne and bird's foot trefoil). Changes in nutrient concentration of forage plants, elevated heat loads and altered feeding patterns of animals may influence rumen physiology. Several promising nutritional strategies are available to lower potential negative impacts of climate change on dairy cow nutrition and performance. Adjustment of feeding and drinking regimes, diet composition and additive supplementation can contribute to the maintenance of adequate dairy cow nutrition and performance. Provision of adequate shade and cooling will reduce the direct effects of heat stress. As estimated genetic parameters are promising, heat stress tolerance as a functional trait may be included into breeding programmes. Indirect effects of global warming on the health and welfare of animals seem to be more complicated and thus are less predictable. As the epidemiology of certain gastrointestinal nematodes and liver fluke is favourably influenced by increased temperature and humidity, relations between climate change and disease dynamics should be followed closely. Under current conditions, climate change associated economic impacts are estimated to be neutral if some form of adaptation is integrated. Therefore, it is essential to establish and adopt mitigation strategies covering available tools from management, nutrition, health and plant and animal breeding to cope with the future consequences of climate change on dairy farming.     

Heat stress,a serious threat to reproductive function in animals and humans

Global warming represents a major stressful environmental condition that compromises the reproductive efficiency of animals and humans via a rise of body temperature above its physiological homeothermic point (heat stress [HS]). The injuries caused by HS on reproductive function involves both male and female components, fertilization mechanisms as well as the early and late stages of embryo‐fetal development. This occurrence causes great economic damage in livestock, and, in wild animals creates selective pressure towards the advantages of better‐adapted genotypes to the detriment of others. Humans undergo several types of stress, including heat, and these represent putative causes of ongoing progressive decay in procreation; an increasing number of remedies in the form of antioxidant preparations are now being proposed to counteract the effects of stress. This review aims to describe the results of the most recent studies that aimed to highlight these effects and to draw information on the mechanisms acting as the basis of this problem from a comparative analysis.     

Development of novel strategies to control foot-and-mouth disease: Marker vaccines and antivirals

Foot-and-mouth disease (FMD) is economically the most important viral-induced livestock disease worldwide. The disease is highly contagious and FMD virus (FMDV) replicates and spreads extremely rapidly. Outbreaks in previously FMD-free countries, including Taiwan, the United Kingdom, and Uruguay, and the potential use of FMDV by terrorist groups have demonstrated the vulnerability of countries and the need to develop control strategies that can rapidly inhibit or limit disease spread. The current vaccine, an inactivated whole virus preparation, has a number of limitations for use in outbreaks in disease-free countries. We have developed an alternative approach using a genetically engineered FMD subunit vaccine that only contains the portions of the viral genome required for virus capsid assembly and lacks the coding region for most of the viral nonstructural (NS) proteins including the highly immunogenic 3D protein. Thus, animals inoculated with this marker vaccine can readily be differentiated from infected animals using diagnostic assays employing the NS proteins not present in the vaccine and production of this vaccine, which does not contain infectious FMDV, does not require expensive high-containment manufacturing facilities. One inoculation of this subunit vaccine delivered in a replication-defective human adenovirus vector can induce rapid, within 7 days, and relatively long-lasting protection in swine. Similarly cattle inoculated with one dose of this recombinant vector are rapidly protected from direct and contact exposure to virulent virus. Furthermore, cattle given two doses of this vaccine developed high levels of FMDV-specific neutralizing antibodies, but did not develop antibodies against viral NS proteins demonstrating the ability of FMD subunit vaccinated animals to be differentiated from infected animals. To stimulate early protection prior to the vaccine-induced adaptive immune response we inoculated swine with the antiviral agent, type I interferon, and induced complete protection within 1 day. Protection can last for 3-5 days. The combination of the FMD marker vaccine and type I interferon can induce immediate, within 1 day, and long-lasting protection against FMD. Thus, this combination approach successfully addresses a number of concerns of FMD-free countries with the current disease control plan. By rapidly limiting virus replication and spread this strategy may reduce the number of animals that need to be slaughtered during an outbreak.     

Oligonucleotide-mediated gene modification and its promise for animal agriculture

One of the great aspirations in modern biology is the ability to utilise the expanding knowledge of the genetic basis of phenotypic diversity through the purposeful tailoring of the mammalian genome. A number of technologies are emerging which have the capacity to modify genes in their chromosomal context. Not surprisingly, the major thrust in this area has come from the evaluation of gene therapy applications to correct mutations implicated in human genetic diseases. The recent development of somatic cell nuclear transfer (SCNT) provides access to these technologies for the purposeful modification of livestock animals. The enormous phenotypic variety existent in contemporary livestock animals has in many cases been linked to quantitative trait loci (QTL) and their underlying point mutations, often referred to as single-nucleotide polymorphisms (SNPs). Thus, the ability for the targeted genetic modification of livestock animals constitutes an attractive opportunity for future agricultural applications. In this review, we will summarize attempts and approaches for oligonucleotide-mediated gene modification (OGM) strategies for the site-specific modification of the genome, with an emphasis on chimeric RNA-DNA oligonucleotides (RDOs) and single-stranded oligonucletides (ssODNs). The potential of this approach for the directed genetic improvement of livestock animals is illustrated through examples, outlining the effects of point mutations on important traits, including meat and milk production, reproductive performance, disease resistance and superior models of human diseases. Current technological hurdles and potential strategies that might remove these barriers in the future are discussed.     

The potential influence of plant-based feed supplements on sperm quantity and quality in livestock: a review

The reproductive performance of male livestock is of economic importance, and improving semen quantity and quality, especially for artificial insemination, additionally helps to avoid the loss of valuable genotypes. The review focuses on the impact of oxidative stress on sperm production and quality in livestock, and the potential role of plant based anti-oxidants to control this impact. From scientific reports dealing with livestock, the paper compiles evidence on effective dietary measures affecting sperm production and quality. Where little or no data are available on livestock, it refers to sources regarding other mammals, including man. The review concentrates on the use of distinct plants as feed supplements rather than on ways to treat deficiencies and imbalances in energy or macro- and micronutrients. Feeding of maca (Lepidium meyenii) and khat (Catha edulis) has been shown to positively affect sperm production and quality in animals. Some evidence points to favourable effects of leucaena (Leucaena leucocephala and Leucaena pallida), sesbania (Sesbania sesban), pomegranate (Punica granatum), tomato (Solanum lycopersicum) and amaranth (Amaranthus hypochondriacus) as well, but studies are either superficial or results are partially contradictory. Finally, the review considers the potential usefulness of medicinal herbs. The list of such plants includes Chinese herbs such as Lycium barbarum, Astralagus membranaceus, Acanthopanacis senticosi, Magnolia officinalis, Cornus officinalis and Psoralea corylifolia and the Indonesian plant Eurycoma longifolia. European candidate plants are Tribulus terrestris and Pendulum murex. Future research should include the screening of other plants, concentrating on the large number of plants rich in metabolites because of their presumed effectiveness. The modes of action often require clarification for the plants with demonstrated effects.