EC legislation requires the land to which free-range poultry have access to be ‘mainly covered with vegetation’, but the nature of this vegetation is not specified. In practice, most free-range land will be grass pasture. Modern poultry nutrition is a highly-developed science, and to house poultry in an environment in which they may consume an unknown quantity of vegetation, itself of unknown nutritive value, introduces uncertainty into a predictable system. In recent years the contribution of grazing to the nutrition of the birds has been considered negligible. However, birds on range appear to ingest a little grass, and therefore the quality of the pasture may affect their performance. If poultry consumed largely grass, then the nutritional value derived from it would be relatively poor. The grass would constitute a source of energy and fibre, but would make little contribution in terms of protein. The likely approach that poultry nutritionists would take is a precautionary one. They would need to know the full nutritive value of the pasture and the likely quantitative intake by the birds, and they would then make adjustments to feed formulations at what they considered to be a ‘safe’ level, in order to minimise the risks of impairing performance. A small (0–5) percentage contribution is probably the most that could be achieved, but given that feed accounts for about 70% of the variable costs of poultry production, such a contribution is economically important.

The domestic pig evolved from the omnivorous wild boar and has retained many natural foraging behaviour patterns. Although most modern commercial pigs are housed and fed concentrate diets, interest in the potential nutrient contribution from pasture has increased due to growth in outdoor and organic pig production systems. The energy requirements of outdoor pigs are increased by approximately 15% under Northern European conditions as a result of greater climatic energy demand and locomotory activity. The nutritional contribution made by pasture will depend on the availability, nutrient composition, grazing intake and digestive utilisation of herbage. Information on these topics is currently very sparse. Herbage availability is often low due to farm rotational policy or destructive foraging by the pigs. Herbage composition shows large varietal and seasonal differences, but the high fibre content reduces the efficiency of energy utilisation and may impair utilisation of other nutrients. Intake of grazed herbage varies widely between individuals, but is typically approximately 2.0 kg DM/d for dry sows fed restricted concentrate, and approximately 0.1 kg DM/d for growing pigs offered ad libitum concentrate. This intake can contribute 50% of the maintenance energy requirement and a high proportion of the amino acid, mineral and trace element requirements of dry sows, but <5% of requirements of growing pigs. Whilst the potential to increase nutrient intakes from grazing exists, this process requires better understanding of herbage intake and digestion, and development of better systems for paddock management.

The main factors affecting the accumulation of potentially-toxic metals (PTM) by grazing animals are the presence of the metal, its concentration in herbage and at the soil surface, and the duration of exposure to the contaminated pasture and soil. In addition, the elapsed time between the contamination of the pasture and grazing, the quantity of soil ingested together with herbage, the mechanism of absorption of the metal into blood and the presence or absence of antagonistic metals can interact to influence the rate and extent of accumulation of heavy metals in edible body tissues. Models of the accumulation of metals by grazing animals may be used to determine the statutory limits of radionuclides and PTM in soils under grazed pastures. Meta-analysis of existing data, using a random-effects model, is a useful approach to understanding the factors affecting the accumulation of some metals, e.g. Cd. The target edible body tissues for the accumulation of most PTM are the liver and kidneys, with the exception of radiocaesium, which accumulates in muscle to a greater extent than in other tissues. The livers and kidneys of mature livestock that have been grazed on areas of pasture at the legal limit of contamination by Cd for more than one grazing season should be removed from the human food chain in order to reduce the risk of intake of Cd by the human population.

Plant secondary metabolites are a natural resource that is largely unexploited in ‘conventional’ animal production systems. They have in the past been generally considered as a source of anti-nutritional factors, and not as a source of exploitable performance-enhancing compounds. Recent and continuing changes to legislation controlling the use of animal feed additives have stimulated interest in bioactive secondary metabolites as alternative performance enhancers. They are broadly compatible with current thinking on the future of agriculture and food in Europe, and with consumer opinion. Interest has been largely on their manipulative role in the digestive and absorptive processes of the hindgut. The present paper will review the use of plants and their extracts to manipulate the rumen microbial ecosystem to improve the efficiency of rumen metabolism. The bioavailability of secondary metabolites and their actions on peripheral metabolism will be considered with a view to improving animal performance. The challenge of delivering plants and their extracts to animals outdoors in a controlled manner will be discussed. Much of what is known about the beneficial roles of plant secondary metabolites on animal performance is circumstantial and is based on tenuous data. In order to more fully exploit their bioactive properties for the benefit of animal performance, modes of action need to be understood. Uptake will be dependent on proven efficacy and consumer acceptance of assurances relating to safety, welfare and the environment.

The constraints to high levels of milk production imposed by a high-quality-pasture diet, and development of feeding strategies to overcome these limitations, were examined by modelling the nutritional status of New Zealand Friesian and North American Holstein–Friesian dairy cows grazing high-quality pasture. The Cornell Net Carbohydrate and Protein System (CNCPS) was used to predict sensitivity of milk production to a 10 % change in the composition of pasture nutrients. The rate at which fibre and protein were degraded in the rumen and the value given to effective fibre and lignin content significantly affected the supply of metabolisable energy and protein, and the profile of amino acid supply. The first limiting factor in milk production when only high-quality pasture was fed was metabolisable energy supply, while specific amino acids, particularly methionine and lysine, limited milk production when > 20 g/kg diet consisted of a grain supplement. Compared with cows fed a total mixed ration in confinement, North American Holstein–Friesians grazing all pasture produced less milk (29.6 v. 44.1 kg/d). Of the difference in milk production 61 % could be attributed to a lower DM intake (19 kg/d v. 23.4 kg/d). Predictions using the CNCPS indicated that supply of metabolisable energy was the first-limiting factor for milk production from high-quality pasture (251 g crude protein (N× 6.25)/kg, 432 g neutraldetergent fibre/kg, 77 % in vitro DM digestibility), rather than metabolisable protein or amino acids. In addition, these nutritional limitations imposed by pasture diets will be greater for dairy cow genotypes that have not been selected for high performance within a pasture system.

Feed formulation to meet nutritional requirements of livestock is becoming increasingly challenging. Regulations have banned the use of traditional high-quality protein supplements such as meat-and-bone meal, pollution from animal excreta of N and P is an issue and antibiotics are no longer available as insurance against the impact of enteric infection and feed anti-nutritional factors. The improved genetic potential of livestock is increasing daily requirement for energy and protein (essential amino acids). To benefit from the enhanced growth potential of livestock diets with high nutrient density are needed that can be formulated from crops without increased cost. Genetic modification of commodity crops used to manufacture animal feed in order to improve the density and quality of available nutrients is a potential solution to some of these problems. Furthermore, crops may be used as biofactories to produce molecules and products used in animal feed with considerable reductions in manufacturing fixed costs. Nevertheless, there are considerable not insurmountable challenges, such as the creation of sufficient economic value to deliver benefit to all members in the feed production chain, which is an essential element of identity preserving and delivering the technology to livestock producers. Individual output traits in the major commodity crops may not provide sufficient value to adequately compensate all the members of the feed production chain. Successful adoption of output traits may rely on inserting combinations of agronomic input traits with specific quality traits or increasing the value proposition by inserting combinations of output traits.

The urgency generated by drug-resistant strains of malaria has accelerated anti-malarial drug research over the last two decades. While synthetic pharmaceutical agents continue to dominate research, attention increasingly has been directed to natural products. The present paper explores the larger context in which plant use occurs and considers how the selection of medicinal plants has evolved over millennia as part of the larger human effort to mediate illness. First attention is directed to indigenous medicinal plants whose anti-malarial activity is based on an oxidant mode of action, by which intracellular constituents lose electrons (become more electropositive). Next, parallels are drawn between these plant substances and a suite of malaria-protective genetic traits: glucose-6-phosphate dehydrogenase deficiency; haemoglobins S, C and E; α- and β-thalassemias. These erythrocyte anomalies are classic examples of Darwinian evolution, occurring in high frequency in populations who have experienced considerable selective pressure from malaria. Characterized by discrete loci and pathophysiologies, they are united through the phenomenon of increased erythrocyte oxidation. In this model, then, oxidant anti-malarial plants are culturally constructed analogues, and molecular mimics, of these genetic adaptations. To further reinforce the scheme, it is noted that the anti-malarial action of pharmaceutical agents such as chloroquine and mefloquine duplicates both the genetic anomalies and the folk therapeutic models based in oxidant plants. This discussion coheres around a theoretical foundation that relates plant secondary metabolites (oxidants) to plasmodial biochemistry and human biological and cultural adaptations to malaria. Co-evolution provides a theoretical link that illuminates how medical cultures manage the relationships among humans, plants, herbivores and their respective pathogens.

Conjugated linoleic acids (CLA) have been shown to have anti-carcinogenic, anti-obesity, anti-atherogenic and immunomodulatory functions. The basis for these effects has not been fully explained, but probably involves effects of CLA on eicosanoid metabolism, cytokine production and\or gene expression. The predominant isomer (85–90%) in the natural sources of CLA has the cis-9, trans-11 configuration. As interest in CLA grew and synthetic forms became available, the number of studies examining the effects of dietary CLA in rodents, human subjects and livestock has increased greatly. In the late 1990 s the observation that CLA had anti-obesity effects was reported. Subsequently, it was determined that this effect in mice could be attributed to the trans-10, cw-12 isomer that, along with the cis-9,trans-11 isomer, predominates in the synthetic forms of CLA. The santi-obesity response varies in magnitude depending on species, and has not been consistent in non-rodents. In general, the response is greatest in mice and less or absent in other species. The basis for this lack of consistency is not clear and is unlikely to be accounted for by differences in the source of CLA. In the pig variation in body fat of animals may account for differences in responsiveness. There is no direct evidence of an anti-carcinogenic effect of CLA in human subjects or livestock. Indirect evidence from in vitro studies with cell lines, as well as epidemiological studies, suggest that CLA may be relevant as a natural anti-carcinogen. The immunomodulatory effects of CLA may have application in livestock production as an alternative to the use of feed antibiotics, or as a means of improving the response to vaccination and conferring disease resistance. The recent literature on the effects of CLA, with emphasis on its anti-obesity effects, is reviewed.

The declining consumption of ruminant products has been partly associated with their high proportion (but not necessarily content) of saturated fatty acids. Recent studies have focused on the less prominent fact that they are also important sources of beneficial fatty acids, including n-3 fatty acids and conjugated linoleic acids. α-Linolenic acid (18: 3n-3) is of particular interest because it also contributes to improved flavour of beef and lamb. Many recent studies showed large effects of special concentrates on levels of fatty acids in milk and meat. However, the ‘rumen protection’ treatments, needed to ensure a worthwhile level of fatty acid in products, are expensive. Herbage lipids are the cheapest and safest source of these fatty acids and so breeding to increase delivery of fatty acids from plants into ruminant products is an important long-term strategy. Plant lipids usually contain high levels of polyunsaturated fatty acids, particularly 18: 2n-6 and 18:3n-3 which are the precursors of beneficial fatty acids. Whilst some plants are particularly rich in individual fatty acids (e.g. 18:3n-3 in linseed), there are also useful levels in grass and clover (Trifolium Spp.). Levels of fatty acids in forages in relation to species and varieties are considered, as well as management and conservation methods. Relationships between levels of fatty acids and existing traits and genetic markers are identified. The effects of forage treatments on the fatty acid content of ruminant products are reviewed. The higher levels of polyunsaturated fatty acids in milk from cows fed clover silages show that the level of fatty acids in herbage is not the only factor affecting levels of fatty acids in ruminant products. Further effort is needed to characterise susceptibility of unsaturated fatty acids to oxidative loss during field wilting and biohydrogenation losses in the rumen, and the relative importance of plant and microbial processes in these losses. The pathways of lipolysis and lipid oxidation are reviewed and other plant factors which offer potential to breed for reduced losses are considered.

Meat quality is a term used to describe a range of attributes of meat. Consumer research suggests that tenderness is a very important element of eating quality and that variations in tenderness affect the decision to repurchase. The present paper highlights recent information on the factors that affect tenderness. While the precise aetiology is not fully understood, a number of factors have been shown to affect tenderness. Of these factors, postmortem factors, particularly temperature, sarcomere length and proteolysis, which affect the conversion of muscle to meat, appear most important. However, it is now becoming clear that variation in other factors such as the muscle fibre type composition and the buffering capacity of the muscle together with the breed and nutritional status of the animals may also contribute to the observed variation in meat tenderness.

Over the last 30 years it has become apparent that specific dietary fatty acids are capable of regulating, either directly or indirectly through various signal pathways, the expression of numerous genes, either positively or negatively. Such nutrient-gene interactions have important effects on cell metabolism, differentiation and growth, and ultimately on disease processes. The present review describes some of the more important fatty acid-gene interactions in relation to health and disease in mammalian species, and focuses on the underlying cell signal mechanisms, including various transcription factors, affected by fatty acids and some of their oxygenated derivatives, e.g. the eicosanoids. The review also attempts to clarify some of the complexities of the effects of fatty acids by suggesting a possible overriding regulation by the redox status of the cell. The latter will at least stimulate controversy in this exciting area of lipid research.

Host-parasite interactions are often seen as an arms race, with parasites attempting to overcome host resistance to infection. Herbivory is a common route of transmission of parasites that represents the most pervasive challenge to mammalian growth and reproduction. The present paper reviews the foraging skills of mammalian herbivores in relation to their ability to exploit plant properties to combat parasites. The starting point is that foraging behaviour may ameliorate the impact of parasitism in three ways; hosts could: (1) avoid foraging in areas contaminated with parasites; (2) select diets which increase their resistance to parasites; (3) select for foods containing anti-parasitic properties (self-medication). Details are given of the pre-requisite skills needed by herbivores if they are to combat parasitism via behaviour, i.e. herbivores are able to: (a) determine their parasitic state and alter their behaviour in relation to that state (behaviours 1, 2 and 3); (b) determine the environmental distribution of parasites (behaviour 1); (c) distinguish plant species or plant parts that increase their resistance to parasites (behaviour 2) or have anti-parasitic properties (behaviour 3). Mammalian herbivores cannot detect the presence of the parasites themselves and must rely on cues such as faeces. Despite the use of these cues contacting parasites may be inevitable and so mechanisms to combat parasitism are necessary. Mammalian herbivores have the foraging skills needed to exploit the heterogeneous distributions of nutrients and parasites in complex foraging environments in order to avoid, and increase their resistance to, parasites. Current evidence for the use of plant secondary metabolites (PSM) by herbivores for self-medication purposes remains equivocal. PSM have both positive (anti-parasitic) and negative (toxic) effects on herbivores. Here details are given of an experimental approach using tri-trophic (plant-herbivore-parasite) interactions that could be used to demonstrate self-medication in animals. There is strong evidence suggesting that herbivore hosts have developed the foraging skills needed to take advantage of plant properties to combat parasites and thus use behaviour as a weapon in the host-parasite arms race.

Early in the co-evolution of plant-animal relationships, some arthropod species began to utilize the chemical defences of plants to protect themselves from their own predators and parasites. It is likely, therefore, that the origins of herbal medicine have their roots deep within the animal kingdom. From prehistoric times man has looked to wild and domestic animals for sources of herbal remedies. Both folklore and living examples provide accounts of how medicinal plants were obtained by observing the behaviour of animals. Animals too learn about the details of self-medication by watching each other. To date, perhaps the most striking scientific studies of animal self-medication have been made on the African great apes. The great ape diet is often rich in plants containing secondary compounds of non-nutritional, sometimes toxic, value that suggest medicinal benefit from their ingestion. Chimpanzees (Pan troglodytes), bonobos (Pan paniscus) and gorillas (Gorilla gorilla) are known to swallow whole and defecate intact leaves. The habit has been shown to be a physical means of purging intestinal parasites. Chimpanzees and man co-existing in sub-Saharan Africa are also known to ingest the bitter pith of Vernonia amygdalina for the control of intestinal nematode infections. Phytochemical studies have demonstrated a wide array of biologically-active properties in this medicinal plant species. In light of the growing resistance of parasites and pathogens to synthetic drugs, the study of animal self-medication and ethno-medicine offers a novel line of investigation to provide ecologically-sound methods for the treatment of parasites using plant-based medicines in populations and their livestock living in the tropics.

Plant phenolic compounds are diverse in structure but are characterised by hydroxylated aromatic rings (e.g. flavan-3-ols). They are categorised as secondary metabolites, and their function in plants is often poorly understood. Many plant phenolic compounds are polymerised into larger molecules such as the proanthocyanidins (PA; condensed tannins) and lignins. Only the lignins, PA, oestrogenic compounds and hydrolysable tannins will be considered here. Lignins slow the physical and microbial degradation of ingested feed, because of resilient covalent bonding with hemicellulose and cellulose, rather than any direct effects on the rumen per se. The PA are prevalent in browse and are expressed in the foliage of some legumes (e.g. Lotus spp.), but rarely in grasses. They reduce the nutritive value of poor-quality diets, but can also have substantial benefits for ruminant productivity and health when improved temperate forages are fed. Beneficial effects are dependent on the chemical and physical structure, and concentration of the PA in the diet, but they have been shown to improve live-weight gain, milk yield and protein concentration, and ovulation rate. They prevent bloat in cattle, reduce gastrointestinal nematode numbers, flystrike and CILt production. Some phenolic compounds (e.g. coumestans) cause temporary infertility, whilst those produced by Fusarium fungi found in pasture, silage or stored grains can cause permanent infertility. The HT may be toxic because products of their metabolism can cause liver damage and other metabolic disorders.

There are now concerns that dietary Se intake is inadequate for the population in the UK and parts of Europe. Many different methods can be proposed to deal with this problem. Experience from Finland suggests that the addition of Se to fertiliser is a safe and effective means of increasing the intake of the micronutrient in the human population. However, careful consideration needs to be given to the potential consequences of increasing Se intake. It is important to understand the biochemical and physiological changes that may occur with any increase in Se intake within the UK population. Se is an essential component of at least twenty functional proteins within mammals. These proteins are essential for a range of metabolic functions, including antioxidant activity, thyroid hormone synthesis and immune function. Thus, any increase in Se intake has the potential to influence in a wide range of factors that may impinge on the incidence of chronic disease. Treatment of soil with Se-supplemented fertiliser will certainly increase total Se in food products derived from areas where this treatment is in place. Consumption of such foods will increase Se status in many populations where the existing intake does not meet requirements. If the increases in Se intake are not toxic the overall consequences have the potential to be beneficial.

Micronutrient deficiencies are a major problem throughout the world and hundreds of millions of the world's population are affected by micronutrient deficiency disorders. In Europe the prevalence of clinical micronutrient deficiency disorders is less than that in the Third World. However, marginal deficiency of some of the micronutrients might be involved in the aetiology of many of the so-called lifestyle diseases, e.g. cancer, cardiovascular diseases, diabetes, osteoporosis. Supplementing domestic animals with micronutrients in excess of their needs could be one strategy to increase the intake and, thereby, status of micronutrients in the human population. This approach should, however, be considered carefully, in relation to both animal and human welfare. Many micronutrients that may accumulate in animal foods are toxic in high doses. It would also be unethical to expose animals to doses that might have deleterious effects on their health, and concentrations in animal products that might have adverse effects when consumed by man should be avoided. Furthermore, food quality should not be impaired by the supplement. On the other hand, to be relevant in relation to human nutrition, the given micronutrient should accumulate in animal tissue in concentrations that make an important contribution to total intake. Finally, the micronutrient should be incorporated in a way and in a form that is bioavailable to man, i.e. is well absorbed and utilized.

Can commonly-eaten food staple crops be developed that fortify their seeds with essential minerals and vitamins? Can farmers be induced to grow such varieties? If so, would this result in a marked improvement in human nutrition at a lower cost than existing nutrition interventions? An interdisciplinary international effort is underway to breed for mineral- and vitamin-dense varieties of rice, wheat, maize, beans and cassava for release to farmers in developing countries. The biofortification strategy seeks to take advantage of the consistent daily consumption of large amounts of food staples by all family members, including women and children as they are most at risk for micronutrient malnutrition. As a consequence of the predominance of food staples in the diets of the poor, this strategy implicitly targets low-income households. After the one-time investment is made to develop seeds that fortify themselves, recurrent costs are low and germplasm may be shared internationally. It is this multiplier aspect of plant breeding across time and distance that makes it so cost-effective. Once in place, the biofortified crop system is highly sustainable. Nutritionally-improved varieties will continue to be grown and consumed year after year, even if government attention and international funding for micronutrient issues fades. Biofortification provides a truly feasible means of reaching malnourished populations in relatively remote rural areas, delivering naturally-fortified foods to population groups with limited access to commercially-marketed fortified foods that are more readily available in urban areas. Biofortification and commercial fortification are, therefore, highly complementary. Breeding for higher trace mineral density in seeds will not incur a yield penalty. Mineral-packed seeds sell themselves to farmers because, as recent research has shown, these trace minerals are essential in helping plants resist disease and other environmental stresses. More seedlings survive and initial growth is more rapid. Ultimately, yields are higher, particularly in trace mineral-‘deficient’ soils in arid regions.

For many nutrients, a systematic determination of the effects of high intakes over extended periods of time has not been conducted. Governments and scientific bodies have just begun to establish the methodology for, and to conduct, nutrient risk assessments for setting ‘tolerable upper levels of intake’ (UL) for nutrients. Nutrient risk assessment provides the framework for using available information to evaluate the safety of nutrients when added to foods or when consumed as supplements, in order to minimize the risks from over-consumption. When intakes are inadequate, food fortification may be the appropriate choice for some nutrients, while in other situations, when requirements are markedly higher for some population subgroups than for the general population, supplements may be the most appropriate intervention. The present paper will present some examples of how to use the UL along with food consumption data to assess the appropriateness of food fortification v. supplementation strategies and to assess their impact on nutrient intakes of the population. The important steps to be followed when evaluating which approach is best are: (a) establishing need, i.e. assessing the gap between current and desired intakes; (b) assessing safety, i.e. consider the margin of safety between requirement and UL as well as the severity and reversibility of the adverse effect that was used to establish the UL; (c) estimating exposure through statistical modelling, in which population-based estimates of intakes before and after the intervention are compared; (d) monitoring the impact of the intervention to ensure that the desired benefits are achieved and that excessive intakes are minimized. This approach can optimize the public health benefits of food fortification or supplement use while minimizing the risks due to excessive intakes.

Uncoupling proteins (UCP) 1 and 2 are members of the subfamily of inner mitochondrial membrane carriers. UCP1 is specific to brown adipose tissue (BAT), where it is responsible for the rapid production of heat at birth. In fetal sheep UCP1 is first detectable at approximately 900d of gestation; its abundance increases with gestational age and peaks at the time of birth. The mRNA and protein for both the long and short form of the prolactin (PRL) receptor (PRLR) are also highly abundant in BAT. Enhanced PRLR abundance in late gestation is associated with an increase in the abundance of UCP1. This relationship between PRLR and UCP is not only present in BAT. Similar findings are now reported in the pregnant ovine uterus, where PRLR abundance reaches a maximum just before that of UCP2. However, the role of PRLR in BAT remains undetermined. Rat studies have shown that PRL administration throughout pregnancy results in offspring with increased UCP1 at birth. Studies in newborn lambs have shown that administration of PRL (20mg/d) causes an acute response, increasing colonic temperature in the first hour by 1°. This increased colonic temperature is maintained for the first 240h of life, in conjunction with enhanced lipolysis. After 70d of treatment there is no difference in the abundance of UCP1 but an increase in UCP1 activity; this effect may be mediated by an increase in lipolysis. Taken together these findings suggest that PRL could be an important endocrine factor during pregnancy and early postnatal life.

Vitamin C is an essential micronutrient. Absence from the diet will result in the deficiency disease scurvy, typically characterised by weakening of collagenous structures. High intakes of vitamin C have been associated with decreased incidence or severity of a number of diseases, including cancer and cardiovascular disease. These beneficial effects may be attributed to its antioxidant properties, although the exact mechanisms of action remain elusive. It is also unclear what intake levels are required for optimal health benefits. The task of defining optimal intakes is hindered by the lack of a reliable functional marker of tissue vitamin C status in man. Many different pathways have been investigated, but none of them have measurable outcome variables relating directly to scorbutic changes. The bone-collagen formation pathway has the potential to provide a functional index of tissue vitamin C adequacy. Vitamin C acts as a cofactor for the enzyme lysyl hydroxylase, which is required for the hydroxylation of lysine residues in procollagen chains. Pyridinoline is a mature collagen cross-link formed from three hydroxylysine residues, deoxypyridinoline is formed from two hydroxylysine and one lysine residue. Guinea-pig studies have shown an alteration in the pyridinium cross-link ratios in response to graded vitamin C intakes ‘Tsuchiya & Bates, 1998’. In order to investigate whether these changes can be seen in a human population group, a study was carried out in rural Gambia, where there is a marked seasonal variation in dietary vitamin C. The present review discusses the rationale behind the study and presents some preliminary results.