Keywords

7.1 Introduction

Extensive production systems can be defined as those systems in which animals have little contact with humans, including infrequent handling (Hodgson 1990). In contrast, in intensive animal production systems there is frequent interaction between animals and their managers. Herbivore species evolved to graze and browse in a variety of ecosystems, such as rangeland, grassland, and open pasture or shrubby and woody landscapes, and a variety of herbivores have been domesticated (cattle, buffalo, sheep, goats, and camels) to be used for production purposes. From the time of their domestication, herbivores have been mainly kept in extensive production systems. Today, there are about three billion animals managed in grazing systems, which use 3.4 billion hectares of land. That means 26 % of the earth’s ice-free land surface is used for animal production (FAO 2009). Developing countries use slightly more of their land mass (~30 %) than developed countries (20.5 %) for animal production. In principle, the welfare of herbivores kept in extensive grazing systems should be assisted by the fact that they have evolved to make the best use of such varied herbivorous environments. However, animals are not always kept where they evolved, and the unpredictability of environmental factors, coupled with the management of livestock by humans, is not always a match to the adaptive features of livestock. Consequently, these mismatches represent welfare problems for livestock kept in extensive systems.

7.2 Why Animal Welfare Is Compromised in Extensive Livestock Production Systems

A key aspect of animal welfare is the ability of an animal to cope with its environment (Broom 1986). Within this functional approach to animal welfare, it is essential to assess whether the biological systems of an animal are functioning in a satisfactory manner in response to environmental changes (Duncan and Fraser 1997). However, welfare not only depends on whether the animal can cope but also on whether coping attempts have negative consequences for the animal. Therefore, there is no simple relationship between challenge and response because multiple biological functions can be affected by a very specific challenge, such as variability in level or quality of nutrition (Blache et al. 2011). Consequently, a multidisciplinary assessment of animal welfare that measures behaviour, the level of productivity, physiology, health, and immunity is required (Gonyou 1986; Broom 1991; McGlone 2001). These multiple aspects of animal welfare are encompassed in the framework designed for animals kept in captive environments known as the ‘Five Freedoms’ (Farm Animal Welfare Council 1993), namely: (a) Freedom from thirst, hunger, and malnutrition, (b) Freedom from discomfort, (c) Freedom from pain, injury, and disease, (d) Freedom to express normal behaviour, and (e) Freedom from fear and distress. Initially the five freedoms framework might not be seen as directly applicable to livestock raised in extensive systems. As pointed out by Turner and Dwyer (2007), extensive systems should not compromise the expression of behaviour, compromise the health of the animals, or induce mental distress, since the animal is in a ‘free range’ or ‘natural’ environment. Thus, some hold the view that livestock in extensive production systems are not under our control and therefore we do not have a duty of care (Appleby 1996). Since these species have coevolved with the landscape to be able to cope with the degree of variability of the environment, how could the welfare of extensive livestock be compromised? The answer is twofold: (1) there is a potential mismatch between the coping capacity of the animals and the variability of the environment of extensive systems because, by controlling stocking density, the type of livestock, and landscape availability, managers control the animal distribution across time and space, and (2) animals kept in the environment they have evolved in can still face challenges from extreme variability in foods, habitats, and environmental conditions that exceed their capacity to cope. The second situation needs to be considered here because, although those factors are not ‘controlled’ by the manager, they represent a welfare challenge.

In the following sections, we will give examples of challenges faced by ruminant livestock either because of natural factors or managerial decisions such as stocking density, choice of species, breed, or timing of breeding. The direct and indirect consequences of each challenge on nutrition will be treated with particular attention since this is a focus of this book. In most codes of recommendations for the welfare of animals, adequate nutrition is one of the primary requirements to be satisfied (Farm Animal Welfare Council 1993; Kyriazakis and Savory 1997). For each challenge, the advantages and limitations of the adaptive behavioural and physiological responses of grazing animals will be presented. We then analyse the impact of these challenges and adaptations on animal welfare under the framework of the aforementioned Five Freedoms. The following challenges are most common and relevant to ruminants kept in extensive conditions: variability of the quality and availability of food and water, the impact of environmental toxicology, predator and fear effects on intake, and competition with conspecifics and non-livestock herbivores.

7.3 Challenge 1: Variability in the Availability and Quality of Food and Water

To fulfil the freedom from hunger and thirst, it is essential that livestock have access to feedstuffs of adequate quality and quantity to be able to meet their nutritional requirements. In extensive livestock production systems, both the quality and quantity of food and water available can be limited either by environmental or managerial factors.

Environmental factors, such as rainfall patterns, drive forage production especially in semiarid and arid systems (Campbell et al. 2006), and food resources can be both variable and unpredictable, and as a consequence, affect grazing productivity (McAllister 2012). Similarly, forage nutritive value can be affected by water availability, fertilisation, and disease because of their impact on plant development (Van Soest et al. 1978).

To optimise production, managers can adopt stocking rate strategies to compensate for the fluctuation in forage supply induced by changing environmental conditions, such as variable rainfall. They can opt for a conservative stocking strategy by maintaining a relatively constant, and low, stocking rate, which would be unlikely to exceed the carrying capacity even during dry years. This strategy aims to avoid vegetation degradation, livestock losses, and potential decreases in animal welfare caused by overstocking in dry years (Campbell et al. 2006). Low stocking rates (i.e. low number of animals on a given amount of land over a certain period of time) typically promote an increase in plant species diversity, although very low stocking rates may reduce plant diversity as a result of competitive exclusion (Grime 1979). At low stocking rates, grazing typically leads to the formation of patches of different forage quality and quantity. In these conditions, herbivores prefer to graze patches of high nutritive quality, which are generally those corresponding to the regrowth of previously grazed areas (i.e. patch grazing; Adler et al. 2001). This recurrent pattern of grazing contributes to the spatial heterogeneity of the vegetation generally observed in plant communities grazed at low stocking rates.

Alternatively to low stocking strategies, managers may adopt high and constant stocking rates, using supplemental feed to maintain high stocking rates during dry years (Campbell et al. 2006). The supplementation needs to be managed carefully because, when stocking rate exceeds the maximum number of animals that can be supported by a certain environment (i.e. carrying capacity), the biomass availability per animal declines and preferred plants (typically the most nutritive in a community) are subjected to a competitive disadvantage relative to non­preferred plants (typically less nutritive or more toxic). The biased grazing leads to changes in plant community structure and composition (Dumont et al. 2007) impacting on both the biomass and the nutritive quality of forage available for grazing (Walker 1995). Herbivores select plant and plant parts at different levels of stocking rates (Provenza and Villalba 2006). However, high animal densities increase competition for food resources and reduce selectivity (Bailey and Brown 2011). Additionally, the prevalence of non-preferred plants species in the context of high animal densities can increase the risk of consumption of poisonous plants (Pfister et al. 2002), which is a reduction in the freedom from disease.

In addition to the compromised freedom from hunger and disease, high animal densities may also induce social stress, meaning there is a decrease in freedom from stress by increased competition for resources. The increase in social stress leads to disturbed grazing patterns that can present some serious welfare issues since the grazing pattern and intensity ultimately affect growth rates in herbivores (Blanc and Theriez 1998).

Independent of climatic conditions, stocking density is one of the most important factors affecting forage availability and quality (Edwards 1980; Allison 1985; De Villiers et al. 1994). While high stocking rates can exacerbate the effects of drought on vegetation by increasing mortality of perennial grasses, negatively impacting on soils and thus contributing to range degradation (O’Connor 1995), conservative stocking rates lead to underuse of forage in wet years which may be inefficient, particularly as environmental conditions (e.g. rainfall across seasons) become more variable. Alternative to the extreme stocking densities listed above, an opportunistic strategy is to change stocking rates to match temporally variable forage supply, aiming to secure quality and quantity forage and therefore insure an adequate level of animal welfare. A variable stocking density strategy means that higher stocking rates are adopted in wet years and reduced stocking rates in dry years. This dynamic strategy aims to match grazing pressure to the existing vegetation in both wet and dry seasons and consequently avoid production losses, and potential declines in animal welfare in dry years (Campbell et al. 2006).

Ranchers now recognise that they not only need to manage to maximise animal production but to improve vegetation abundance and plant species composition and to enhance the ecological integrity of their operations (Grissom and Steffens 2013). Under this framework, they implement adaptive management strategies with variable timing, frequency and distribution of grazing with positive economic returns and benefits to animal welfare.

7.3.1 Adaptive Responses to Low Quantity and Quality Forage

To match nutrient intake to requirements, herbivores have developed adaptive responses to decreases in the amount and/or quality of food available. These adaptive strategies include modification of feeding behaviour such as diet selection, or changes in foraging time, or modification of social behaviour such as dispersion. However, in extreme cases the adoption of feeding strategies or changes in social behaviour can negatively impact on welfare.

7.3.2 Diet Selection

The selection of a feeding station by herbivores in a heterogeneous landscape has been described as a hierarchical decision process which takes place at different levels: the regional level, landscape, plant community, down to the individual plant and its parts (Senft et al. 1987). According to optimal foraging theory, when food availability changes in space and time, herbivores will focus on the most profitable foods if resources are abundant (MacArthur and Pianka 1966; Stephens and Krebs 1986), and broaden their diet when the availability of resources declines (e.g. dry season, drought, winter) (Owen-Smith and Novellie 1982; Stephens and Krebs 1986). In terms of habitat use, the selection process may lead to an ideal free distribution of grazing pressure among habitats of different qualities (Fretwell and Lucas 1970). Thus, optimality models suggest that as long as the stocking density is adequate, animals should not experience any form of malnutrition.

Most models used in optimal foraging theory use energy or protein as the currency to be maximised. Lambs and goats fed diets low in energy and protein prefer flavoured foods associated with intra-ruminal infusions of energy (starch, propionate, acetate) and nitrogen (urea, casein, gluten), respectively (Villalba and Provenza 1996, 1997a, b, c; Duncan and Young 2002). Thus, herbivores are able to associate different internal states with the ingestion, or lack thereof, of different nutrients (Egan 1980; Kyriazakis and Oldham 1993). Despite the importance of energy and nitrogen, foraging animals usually face a choice of a variety of habitats and they possess multiple nutrient requirements. Thus, models based on just one currency (e.g. energy) are poor predictors of habitat occupancy (Wallis de Vries and Schippers 1994). Complementary nutrients like phosphorous have improved those predictions in free-ranging cattle (Wallis de Vries and Schippers 1994). Consistent with this, lambs deficient in phosphorous and calcium increase preferences for flavours and supplements which provide those minerals (Villalba et al. 2006, 2008). Thus, a decrease in the diversity of foods and/or habitats may compromise animal welfare (Manteca et al. 2008; Villalba et al. 2011; Catanese et al. 2013). The inability to satisfy requirements for energy, protein, and minerals can lead to nutritionally unbalanced intake, health problems, and stress. In an unbalanced nutritional environment, animals may stop eating because their requirements for the nutrient in highest concentration are rapidly satisfied without reaching the requirements for nutrients in lower concentrations, a phenomenon known as incidental restriction (Raubenheimer 1992). Alternatively, the animal may continue foraging in order to satisfy the requirements for nutrients in lower concentrations, inevitably leading to overconsumption of the nutrient in highest concentration, a phenomenon known as incidental augmentation (Raubenheimer 1992). Excessive nitrogen concentrations can lead to ammonia build-up in the blood resulting in loss of appetite, infertility, and even death (Lobley and Milano 1997). In addition, the augmentation in nutrient-rich and homogeneous food environments will compromise animal welfare because excess nutrients can induce aversive behaviour (Provenza 1996). Lambs exposed to flavours associated with high doses of energy or nitrogen become averse to those flavours (Villalba and Provenza 1996, 1997a, b), suggesting that excesses of nutrients can be a source of stress. The provision of multiple alternatives regarding foods and habitats is necessary to reach the appropriate proportion of required nutrients (Bailey and Provenza 2008) and allow a ruminant to adjust its food selection to minimise the discomfort generated by several signals produced during the ingestive process, i.e. the supply of metabolisable energy, crude protein, and neutral-detergent fibre (Forbes 2007; Gregorini et al. 2015). In contrast, animals that cannot express their diet preferences may experience frustration (Rutter 2010) or negative postingestive feedback (Forbes 2007; Villalba et al. 2010b) and therefore have a compromised welfare.

7.3.3 Foraging Behaviour

Herbivores can vary greatly the time they spend feeding in response to pasture availability and quality. Ruminants adapt to poor forage conditions by modifying the biting rate (number of bites per unit time), bite weight (amount of food taken per bite), and total grazing time (Holmes 1989) to obtain the necessary daily herbage intake. On short overgrazed pasture, herbivores are not able to sustain the bite volume (Charcon and Stobbs 1976) and, because of the reduction in stratum bulk density (Burlison et al. 1991), the bite weight decreases relative to its optimal level (Arriaga-Jordan and Holmes 1986). Consequently, to maintain intake, grazing ruminants have to graze for longer periods as forage conditions deteriorate (Squires 1981; Arnold 1985a; Lu 1988). On good pastures, domestic ruminants graze between 4 and 9 h/day (Houpt 1991), whereas, on poor forage conditions, grazing times of up to 14 h have been recorded (Arnold and Dudzinski 1978). This increase in grazing time, which includes an increase in total jaw movements and walking, can lead to fatigue before nutritional requirements have been fulfilled (Williamson and Payne 1978; Birrell 1991). Consequently, daily energy requirements increase because animals walk more per unit of grazing time (Osuji 1974). For example, grazing ruminants require more energy than penned ruminants: 10–50 % for sheep (Holmes 1989) and 25 and 75 % for goats (NRC 1981).

The physical characteristics of the plant can also affect grazing time. The fibrousness of feed is positively correlated with total chewing time (Boever et al. 1990). It would be difficult to consider this parameter to assess the welfare of ruminants because chewing efficiency is also affected by age (older animals chew feed less efficiently than younger ones, Gill et al. 1966), body weight (larger animals eat faster than small ones, Deswysen 1986), pregnancy (pregnant animals need more chewing time per kg of dry matter than non-pregnant ones, Campling 1966), jaw force (Hooper and Welch 1983), number of chews per unit time (Grummer et al. 1987), percentage of true chewing (Deswysen et al. 1987), and tooth surface area (Welch and Smith 1970). On the other hand, animals can adapt to the physical characteristic of the forage by developing specific foraging skills (Flores et al. 1989a; Hodgson 1990). For example, lambs used to eating a particular kind of plant were more efficient at foraging from it than unfamiliar lambs (Flores et al. 1989b, c). It has to be noted that these specialised grazing techniques may be unsuitable for other types of plant communities (Arnold and Maller 1977) and could limit the feeding behaviour of animals moved between very different plant communities.

7.3.4 Dispersion

The degree of dispersion of grazing animals is measured as a function of the distance between individuals of the same group, mean group size, and the distance between groups (Arnold 1985b). Dispersion is a strategy that enables animals to find scattered pockets of forage and to avoid competition for food. As forage conditions deteriorate, animals tend to split into increasingly smaller subgroups, and the distance between these subgroups also increases (Dudzinski et al. 1978). Inter-individual distance depends mainly on the breed. In sheep, for example, the distance between nearest neighbours is much greater in hill breeds than in Merinos (Arnold 1985b). On poor pastures, Merino sheep remain as a single flock in most circumstances (Lynch 1974), whereas many other breeds form subgroups under almost all conditions (Arnold 1985b). Similar differences in dispersion strategy between breeds have been reported in cattle (Hall and Moore 1986). In breeds with limited dispersion the ability to feed on poor pastures becomes restricted (Kilgour et al. 1975). Dispersion is an effective adaptation to changes in pasture quality and availability; however, the welfare of gregarious animals could be compromised because when forage conditions deteriorate, dispersion may conflict with their natural social behaviour. Assessing the impact of dispersion on the social structure is not simple because some breeds can balance the need for social contact with the need to disperse. Hill sheep are highly social during winter, living in large subgroups influenced in their movements by other group members. In summer, however, there is a marked decrease in gregariousness, with a considerable reduction in subgroup size and reduced frequency of cohesive grazing behaviour. The summer behaviour corresponds with the growth of dispersed patches of grass (Hunter and Milner 1963; Lawrence and Wood-Gush 1987, 1988). In addition to breed, dispersion is also affected by other factors such as previous experience (Zimmerman 1980), maternal experience (Key and MacIver 1980), location of preferred feed such as specific plant communities (El Aich and Rittenhouse 1988) or feedblocks (Lawrence and Wood-Gush 1988), shade (Fowler 1984), and water source (Squires 1981).

7.3.5 Water Intake

Ruminants can go longer without food than they can without water, so their welfare is very much dependent on the ease of access to drinkable water. In intensive or semi-intensive animal production systems, livestock are either watered daily or allowed to drink whenever they like. In contrast, under pastoral conditions, livestock access watering points and develop rigorous watering regimes that vary from every 3 days in cattle and donkeys, through 5 days in sheep and goats, to 7–15 days in camels (Nicolson 1984). However, the frequency of drinking is affected by the level of humidity and ambient temperature. For example, in the Australian arid zone, Merinos drink every day and twice a day when ambient temperature exceeds 35 °C (Dawson et al. 1975).

Within species, breeds differ in their adaptation to water restriction. For example, Boran cattle have large intakes of water and the intake is faster than other breeds. Boran bulls can drink up to 105 L in 6 min without suffering water intoxication, whereas temperate cattle can only drink at a third of this rate safely (Nicolson 1984). In sheep, when the distance between food and water is short, Merinos and Border Leicesters drank twice per day, but when the distance exceeded 3.2 km, Merinos drank once per day while Border Leicesters continued drinking twice daily until the distance reached 4.8 km (Squires and Wilson 1971).

To access water, livestock may have to spend time walking long distances between watering points and grazing grounds (Squires 1981) that reduces time available for grazing (El Aich et al. 1991). The time spent travelling back and forth to the watering point depends on (1) the animal’s need for water, which itself depends on species, breed, climatic conditions, water content of the forage, and water quality, (2) the distance to travel, and (3) the walking speed. All of these factors should be taken into consideration when assessing the welfare of livestock kept in extensive systems.

7.4 Challenge 2: Variability in the Toxicological Environment

In extensive grazing systems, animals encounter a diversity of plants and many of those contain plant secondary compounds (PSC), especially if the animals are grazing native ‘unimproved’ pasture (Estell 2010). Plants produce secondary compounds for many reasons, mainly as a defence mechanism in response to herbivory and other environmental stressors such as disease and competition (Cowan 1999; Mazid et al. 2011). More than 200,000 chemical structures have been identified as PSC, including flavonoids, tannins, saponins, alkaloids, non-protein amino acids, cyanogenic glycosides, glucosinolates, and terpenes (Cowan 1999; Bernhoft 2010). The chemical diversity of PSC is the basis of the diversity of their actions on animal’s organs and systems, as well as on animal behaviour (Durmic and Blache 2012). A specific PSC can have both detrimental and/or beneficial effects on animal welfare depending on the form and the dose ingested, the duration of ingestion, and the species exposed (Greathead 2003; Bernhoft 2010). Plant secondary compounds can severely alter nutrient utilisation, digestive function, respiratory and cardiovascular function, immune function, as well as impacting on the nervous system and reproductive capacity (Vercoe et al. 2009).

Feed intake and feed efficiency can be reduced by PSC because they influence diet selection and grazing behaviour (Provenza and Villalba 2006). Plant secondary compounds can be bitter and often deter animals from eating the plant or interfere with the digestive and fermentation process and can directly affect host secondary metabolism. However, the dose and mix of PSC are critical. Ingestion of PSC can reduce feed conversion efficiency (Stienezen et al. 1996), while small quantities of some PSC can increase it (Carulla et al. 2005). Similarly, fibre digestion can be reduced (Patra and Saxena 2009), not affected (Wang et al. 2009), or stimulated (Hart et al. 2007) by PSC. The decrease in digestibility by PSCs is associated with the inhibition of ruminal protozoa, cellulolytic bacteria, and fungi (Ferme et al. 2004; Sivakumaran et al. 2004) and a general inhibition of microbial fermentation and microbial synthesis in the rumen (Oh et al. 1967, 1968; Nagy and Tengerdy 1968; Lu and Jorgensen 1987).

In addition to these specific impacts on intake and rumen function, PSC can affect all the components of the digestive system of herbivores, inducing gastroenteritis, ruminal atony (Aslani et al. 2004), lower viscosity of intestinal content (Mahgoub et al. 2008), and liver damage (Waghorn 2008), as well as bladder lesions (Sardon et al. 2005), renal disease, and kidney failure (see Durmic and Blache 2012).

It is not only the digestive system that is impacted by PSC as pointed out in a recent review by Durmic and Blache (2012). The respiratory system can also be dramatically affected after the ingestion of PSC, leading to serious health problems such as alveolar emphysema and pulmonary necrosis and edema in sheep and cattle (Wilson et al. 1977). Similarly, with the cardiovascular system, ingestion of PSC can lead to cardiac arrhythmia, haemorrhagic syndrome and cardiac necrosis, and haemolysis. Plant secondary compounds can act as foreign molecules and induce inflammation and reduced immune cell count and activity and cause anaemia, or act as anticoagulants. Photosensitisation and irritation can be common in animals consuming plants rich in some PSC, such as saponins and furanocoumarins (Revell and Revell 2007; Bernhoft 2010). The effects of PSC on the nervous system are often detrimental and can be lethal, for example, some alkaloids, cardiac glucosides, and cyanogenetic glucosides are powerful neurotoxics (Ingebrigtsen 2010).

The reproductive capacity of both males and females is also impacted by PSC, with some dramatic consequences on production and welfare [for review see Blache et al. (2008), Durmic and Blache (2012)]. PSC can stimulate the expression of male reproductive behaviours (Patel et al. 2011) but can also decrease sperm production and quality. In females, PSC that affect fertility can be grouped into plants with contraceptive, anti-implantation, and abortifacient activity (Kumar et al. 2012).

Although PSC, as described above, have a large range of negative impacts on health, welfare, and the productivity of livestock, ruminants have acquired adaptive features that allow them to cope with the presence of many PSC in pasture because of co-evolution. More importantly, managers of extensive livestock systems can also take advantage of the beneficial impacts of PSC on bodily function to improve both the quality of animal production and animal welfare without compromising productivity.

7.4.1 Herbivores Adaptations to Cope with PSC

The adaptive features that allow herbivores to cope with PSC include behavioural and metabolic adaptations (Foley et al. 1999). The main behavioural adaptation is the capacity of herbivores to develop food aversions when ingesting PSC, because some of these compounds induce nausea (Provenza 1996). These aversions restrict the intake of toxin-containing plants, an outcome that contributes to enhanced fitness of herbivores to a particular environment. The presence of PSC such as alkaloids (e.g., Delphinium spp.; Pfister et al. 1997), condensed tannins (e.g. Coleogyne ramosissima Torr.; Provenza et al. 1990), and terpenes (e.g., Artemisia tridentata Nutt.; Dziba et al. 2006; Juniperus spp. Utsumi et al. 2009) reduced feed intake in cattle, sheep, and goats. However, not all PSC cause food aversions (Pfister et al. 2010) and delayed toxic effects can limit the ability of herbivores to form food aversions. For instance, because horses do not develop a food aversion when illness is delayed they may be at risk for long-acting toxins like the alkaloids found in Senecio and Equisetum species (Houpt et al. 1990). Plant secondary compounds can also reduce forage digestibility and increase acidic burdens in consumers with negative impacts on intake and productivity (Foley et al. 1995, 1999).

The digestive system of herbivores has metabolic adaptations aimed at the detoxification of the ingested PSC (Freeland and Janzen 1974; Illius and Jessop 1995). However, detoxification comes with a substantial metabolic cost (Thomas et al. 1988; Sorensen et al. 2005) so adequate supplies of nutrients need to be available or provided by the livestock manager (Illius and Jessop 1995). The consumption of a diversity of PSC may reduce the overall toxic effect of the mix because (1) diluted mixtures are less toxic to herbivores as each individual PSC may be detoxified by a specific pathway (Freeland and Janzen 1974), thereby eliminating a risk of saturation of detoxification mechanisms, and (2) the formation of gastrointestinal complexes often reduces the absorption and activity of single compounds. For example, tannins and saponins chelate each other in the gastrointestinal tract. It has been shown that by appropriate diet selection, mice can choose a mix of feeds containing tannins and saponins in a way that nullifies the effect of each compound (Freeland et al. 1985). Likewise, goats have a greater feed intake when they are offered shrubs containing a combination of tannins and saponins, compared to when they are offered single shrubs (Rogosic et al. 2006).

7.4.2 PSC as Medicinal Compounds for Herbivores

As pointed out at the beginning of this section, plant secondary compounds can have positive effects on some bodily functions when they are ingested in the right quantity, for the right amount of time, or in the right combination. These medicinal effects of PSC have a great potential to improve both the health and welfare of ruminants kept in extensive systems, where the provision for animal health by managers is limited.

Internal parasites are one of the greatest disease problems in grazing livestock worldwide (Min and Hart 2003; Waller 2006). Failure to control gastrointestinal nematodes typically results in poor growth rates, ill-thrift, and death (Min et al. 2004). Considerable attention has been given recently to bioactive plants that affect internal parasite populations (Jackson and Miller 2006), such as plant-derived tannins, alkaloids, terpenes, saponins, and sesquiterpene lactones (Hoskin et al. 1999; Kayser et al. 2003; Hernández-Villegas et al. 2011). Several in vitro and in vivo studies have suggested that condensed tannins can have anthelmintic effects against ruminant nematode parasites. Livestock feeding on plants with tannins, such as sulla (Hedysarum coronarium) (Niezen et al. 1998, 2002), sainfoin (Onobrychis viciifolia; Paolini et al. 2003), Sericea lespedeza (Lespedeza cuneata; Shaik et al. 2006), heather (Calluna vulgaris; Osoro et al. 2007), a number of acacia species (for instance, Acacia cyanophylla; Akkari et al. 2008), and lentisk (Pistacia lentiscus; Landau et al. 2010), have lower faecal egg counts—an indirect measurement of parasitic burden—than those eating plants of similar quality, or the same rations without tannins. These actions result from several physiological mechanisms such as a direct anthelmintic effect (Athanasiadou et al. 2001), impaired larval establishment (Brunet et al. 2008), decreased parasitic nematodes fecundity in females (Martínez-Ortiz-de-Montellano et al. 2010), and increases in the supply of by-pass protein that enhances immune responses to intestinal parasites (Niezen et al. 2002; Min and Hart 2003). Recent results suggest that parasitised sheep and goats increase preferences for antiparasitic PSC when experiencing parasitic burdens relative to non-parasitised animals (Gradé et al. 2009; Osoro et al. 2007; Martínez-Ortiz-de-Montellano et al. 2010; Villalba et al. 2010b; Juhnke et al. 2012).

In addition to the control of gut pathogen load (Patra and Saxena 2009), PSC can facilitate rumination, prevent/cure bloating (Viegi et al. 2003), reduce acidosis (Hutton et al. 2010), reduce diarrhoea and constipation (McGaw and Eloff 2008), reduce kidney stones, and treat cystitis (Viegi et al. 2003). Moreover, some PSC can increase the protection of dietary proteins and reduce microbial proteolysis, peptidolysis, deamination, and degradation to ammonia, allowing nitrogen to escape to the duodenum and improve nitrogen utilisation and production (Waghorn 2008). The energy utilisation of feed can be increased by some PSC by reducing the amount of methane that is produced during fermentation (Bodas et al. 2008; Vercoe et al. 2009).

Some PSC have antitussive, emollient, and expectorant properties that improve lung function [for review see Durmic and Blache (2012)]. In the cardiovascular system, PSC can have positive impacts through hypotensive, cardioprotective, and vascular-stabilising actions (Svendsen et al. 2010). Consumption of PSC may also modify the immune system and blood composition. Some PSC stimulate the immune system because they enhance both innate and specific immunity via modulation of receptors, enzymes, and immune molecules and have anti-inflammatory properties (Provenza and Villalba 2010). At the skin level, PSC can help wound formation, reduce skin irritation, and be used to treat some skin diseases and ectoparasites. Some PSC have structural and functional similarity with benzodiazepines and have been exploited for their calmative and anxiolytic activity in livestock (Durmic and Blache 2012). While the mechanisms of action remain largely unknown, plants containing saponins, alkaloids, and tannins have been used in ethno-veterinary practices to improve the welfare of animals during, and around the time of, parturition by reducing dystocia, improving expulsion of the placenta, and recovery from difficult parturition (Viegi et al. 2003).

Overall, as long as the types and amounts of PSC can be managed, the medicinal properties of PSC described above hold exciting opportunities for the improvement of animal health and welfare and the productivity of large numbers of ruminants grazing poor quality (high fibre and low protein) diets while reducing ecological impact.

7.5 Challenge 3: Variability in the Thermal Environment

Animals are raised in extensive grazing systems located in very different climates, from temperate pastures (e.g. New Zealand), rangelands in extreme climatic zones (Texas, Patagonia, north-west Australia), Mediterranean grasslands (Western Australia, Israel, Uruguay), and tropical lowlands [Colombia; See part 3 of Hodgson and Illius (1996)]. Consequently, ruminant livestock can be exposed to temperatures varying from −20 to +50 °C. Ruminant species are generally well adapted to a range of ambient conditions; hence they can, through the process of thermoregulation, maintain homeostasis and the functioning of all physiological systems, over a broad range of temperatures. Thermostasis is important because most extensively managed livestock are mammals, and mammalian biochemical systems function optimally over a limited body temperature range. The range of ambient temperatures within which an endotherm can regulate its temperature without elevating its metabolic rate or evaporative water loss is called the thermoneutral zone (IUPS Thermal Commission 2001). The range of both the thermoneutral zone (the range of environmental temperatures where the cost of thermoregulation in minimal) and the thermoregulatory zone (the range of environmental temperatures where an animal has the capacity to maintain a stable core temperature) depends on the evolutionary history of a given species or breed (Table 7.1). The values for the thermoneutral range given in Table 7.1 are not absolute, as there are phenotypic and genetic differences within and between genotypes. For instance, there are differences in heat tolerance (e.g. estimated through panting score, tympanic temperature, respiration rate) between heat-tolerant, cold-intolerant Bos indicus cattle and heat-intolerant, cold-tolerant Bos Taurus (Hansen 2004; Gaughan et al. 2009). Livestock exposure to particular environments in high or low latitudes may lead to environmental adaptations that will also modify the thermoneutral ranges as animals adapt to local environments physiologically and behaviourally (Provenza 2008).

Table 7.1 Core temperature and thermoneutral range in different species [data from Brody (1945), Hahn (1999), Robertshaw (2004)]
Full size table

Extreme variations in temperature can compromise the welfare and the production of ruminants if the conditions exceed the limits of the breed/species to balance heat gain with heat loss to maintain a constant body temperature. Heat gain is the sum of metabolic heat produced by all exothermic biological reactions occurring in the body, including digestion and rumen fermentation, plus any environmental heat, such as solar radiant heat or convective heat gain when ambient temperature exceeds skin temperature. Heat loss from an animal occurs via four routes: conduction, convection, radiation, and evaporation (Jessen 2001).

7.5.1 Ruminants Coping with Thermal Stress

Since breeds and species of production animals are translocated to new grazing systems, such as highly productive dairy cattle transported to the tropics, the capacity of each breed to thermoregulate can be compromised when there is a mismatch between environmental conditions (humidity, maximum, and minimum temperature) and thermoneutral zone for the species or breed. Then animals are said to be heat or cold stressed when they are in an environment that is above or below the thermoneutral zone, respectively. Being heat or cold stressed does not mean that an animal’s welfare is compromised because endothermic animals (mammals and birds) have evolved physiological mechanisms and capacities that defend body temperature in the face of thermal stress. The adaptations of ruminants to temperature stresses involve physiological and behavioural mechanisms aiming at controlling the production or loss of heat.

7.5.2 Adaptive Control of Heat Production

During cold stress, when the environmental temperature is below the thermoneutral zone, an animal must increase heat production. Cold stress thus induces an appropriate increase in heat production through increased metabolic rate, including shivering. The elevated metabolic rate then requires a matching increase in energy intake if energy balance is to be maintained. However, the required increase in food intake is possible only if forage is readily available and of high digestibility, which is not always the case. For example, both parameters decrease dramatically when the ambient temperature reaches freezing (Adams et al. 1986; Adams 1987). The capacity of individuals to sustain the elevated metabolic rate required to achieve heat balance in the cold depends on other factors such as health status and energy stores. For example, significant mortality rates have been seen in sheep exposed to cold weather and deprived of shelter in the first few days after shearing (Lynch et al. 1980). Even in the absence of mortality, the maintenance requirement increases during cold stress, so there is less energy available within the animal for production or growth. Shelter during cold weather may be provided by long dry grass to sheep at low stocking rates. Nevertheless, the lower quality of the food resource will lead to increased grazing time relative to the absence of shelter (Arnold and Dudzinski 1978).

Since heat gain can be increased by environmental heat, such as solar radiant heat, animal exposed to high temperature will seek shade. For instance, cattle in hot weather actively seek shade, which may reduce the radiant heat load by at least 30 % (Blackshaw and Blackshaw 1994). Thus, the provision of trees and shrubs is an important source of shade for hot weather and can improve the welfare and productivity of ruminants during periods of low environmental temperatures as well.

During heat stress, ruminants can decrease heat production by reducing food intake and rumination time, because digestion is an exothermic process. In sheep, heat stress induces decreases in food intake, feed efficiency, and utilisation, a disturbance of enzymatic reactions, hormonal secretions, and blood metabolites, all of which modify water, protein, energy, and mineral balances (Marai et al. 2007).

7.5.3 Adaptive Control of Heat Loss

Mammals use a range of physiological and behavioural mechanisms to increase heat loss during exposure to heat, including increases in evaporative heat loss, adoption of specific behaviours and body postures, and changes in daily patterns of activity and social group dynamics. In extreme heat, mammals rely on the most powerful form of heat loss, evaporative water loss, via panting or sweating. While the evaporation of water from the respiratory tract or general skin surface can help to maintain core body temperature, it also creates osmotic strain, and as such the welfare implications of heat stress are context dependent. Hot and humid conditions are more stressful than hot and dry conditions, because evaporation requires a vapour pressure (humidity) gradient. High absolute humidity reduces the amount of heat that an animal can dissipate by evaporative water loss. To increase evaporative water loss, the animal exposed to heat stress needs to have access to drinking water to avoid dehydration.

In hot conditions, grazing animals adopt behaviours that promote passive heat loss by convection and radiation, preferring, for example, areas with high wind speed and shaded areas where they can avoid direct solar radiation. Cattle exposed to heat stress will prefer to stand instead of lying down, and sheep spread their hind legs thereby exposing the well-vascularised skin under the flanks and promoting convective heat loss (Campbell et al. 1969). During prolonged exposure to high temperatures, cattle, bison, goats, and sheep change their daily activity pattern, shifting grazing activity to the coolest hours of the day (evening) and even switching to nocturnal grazing (Vallentine 2000). In cattle, breed has a strong effect on the impact of hot conditions. Bos primigenius indicus cattle are well adapted to heat, and breeds of indicus cattle and those derived from crosses with European breeds (Brahman and Tuli for example) spend less time in the shade and more time grazing than European breeds such as Angus (Forbes et al. 1998).

Heat stress may have a greater impact on welfare than cold stress because the ‘safety margin’ between normal core temperature and lethal hyperthermia is smaller than that for lethal hypothermia. In addition to the impact on welfare, exposure to heat and cold stress causes a decrease in production, because thermoregulation, directly or indirectly, costs energy. For example, it has been estimated that thermal stress could account for an increase of about 40 % in the maintenance energy requirements of range beef cows (Ames 1985). While thermoregulatory costs are reflected in decreased productivity (Webster 1991), the maintenance requirements of ruminants increase linearly during cold stress but exponentially during heat stress (Ames and Ray 1983). In cattle in the Southern USA, fertility is reduced from around 50 % in winter to less than 15 % in the summer (Thatcher and Collier 1986). At the extremes of climatic conditions it is not just productivity that decreases, but the animals themselves can be at risk.

7.6 Challenge 4: Pressure from Environmental Fauna

In extensive systems, livestock share the environment with other animals that either compete for the same resources, prey on them, or parasitise them. In all cases, herbivores have adaptive responses, but these responses are not always optimal and can compromise both their welfare and productivity.

7.6.1 Competition for Resources

According to niche theory, all species differ to some extent in the resources they use (Prins and Fritz 2008). In mammalian herbivore assemblages, different species of herbivores can be classified into grazers, browsers, and mixed feeders because of differences in morphophysiological adaptations and ‘feeding types’ (Hofmann 1984, 1989). Therefore, cohabitation between two species with morphophysiological differences will not translate to an overlap among their diets. In contrast, if two or more herbivore species have similar morphophysiological adaptations, they will share food resources and, in periods of short supply, the performance of at least one of the species will decrease (Mishra et al. 2004). The intensity of resource competition is greater in areas of low productivity or during periods of low resource availability (e.g. in seasonal environments during the dry season). As an animal species gets outcompeted from preferred resources, it is likely that members will increase the consumption of less suitable forage (Gordon and Illius 1989), which in turn will negatively impact their nutrition and welfare. However, the presence of competitors can also have a positive effect on diet quality of livestock if the resources are abundant, a phenomena called facilitation. For example, the presence of wild ungulates depressed the food intake and performance of cattle during the dry season (competition), but their presence enhanced diet quality and performance of cattle during the wet season (facilitation; Odadi et al. 2011). In the Serengeti, buffalo and zebra feed on and trample taller and coarser grasses, clearing the way for smaller herbivores (e.g. gazelle) to feed on exposed plant parts of higher nutritional quality (Bell 1971). In extensive systems, it is possible that the feeding behaviours of one species improve the feeding efficiency of individuals of one or more coexisting species. Thus, some wild and domestic species may improve their welfare and nutrition through facilitative interactions (Prins and Fritz 2008; duToit 2011).

7.6.2 Cost of Predation

In addition to the obvious impacts of predators directly killing herbivores (i.e. lethal effects), predators have significant nonlethal impacts on their prey (Edwards 1983; Hernández and Laundré 2005). They may scare their prey, not just when they are about to attack (Brown et al. 1999), but they establish a ‘landscape of fear’ for herbivores with a topography determined by the level of perceived predation risk (Laundré et al. 2001). The response of herbivores to predator presence impacts on their feeding behaviour, nutritional status, and social structure, all potentially leading to decreased welfare. In the presence or perception of predators, herbivores sacrifice feeding effort and invest more time in vigilance and shift from riskier to safer feeding stations (Edwards 1983; Hernández and Laundré 2005). For example, in elk, the reintroduction of wolves into Yellowstone National Park has led to an increase in vigilance and a decrease in feeding rates (Laundré et al. 2001). The estimated 20 % decline in foraging effort by female elk compromised survival rates and led to a decrease in the birth mass of calves during the spring (Laundré et al. 2001).

Predator presence, or the perception of predator pressure, impacts on the quality of the forage consumed by herbivores. In the absence of predation, the prey selects the highest quality habitats, but in response to predators, the prey moves to poorer quality habitat, resulting in decreased diet quality (Edwards 1983). For instance, elk in Yellowstone National Park now use forest edge areas more than open meadows, although elk preferred open meadow areas before the release of wolves in the park (Hernández and Laundré 2005). Together the ‘lost opportunities’ to feed in profitable patches, which are presumably perceived as risky and the increase in time and effort invested in vigilance and apprehension, lead to an increase in the energy cost of predation by reducing nutrient intake and increasing energy expenditure. Even small changes in habitat may lead to large increases in the cost of predation (Brown and Kotler 2004). When the predation pressure increases so much that the animals are not able to meet their nutritional requirements, both productivity and welfare can be dramatically compromised. To assess and manage the impact of predation, in addition to accounting for the killing of animals, it is possible to measure the times at which herbivores quit eating a preferred forage, activity levels in time and space, and habitat distributions with and without perceived predation risk (Brown and Kotler 2004).

7.6.3 Parasitic Insects

In extensive systems, it is not possible to control for insect infestation, such as flies. The effect of insects can be direct, such as the Australian sheep blowfly (Lucilia cuprina) that is responsible for initiating most blowfly strikes, or indirect, such as flies causing continuous irritation that led to a reduction in grazing time and a decrease in nutrient intake (Lefcourt and Schmidtmann 1989). In bad seasons, sheep may lose a large amount of grazing time due to harassment by Oestrus ovis flies (Blood et al. 1983). Ungulates have adopted individual and group behaviours to reduce fly irritation. By lying down, animals reduce the exposure of body surfaces, decrease the production of some fly attractants (e.g. sweat and carbon dioxide), and dislodge fewer flies from foliage (Espmark and Langvatn 1979). When forage conditions are poor, animals need to increase their grazing time, walk more while grazing, and have difficulty to lie down and avoid fly irritation. Social grouping is also used as a means to reduce fly harassment. As groups become larger, each individual attracts fewer flies (e.g. Duncan and Vigne 1979). Social grouping creates a clear conflict with the increased dispersion of animals associated with poor forage conditions.

7.7 Knowledge Gaps

Within the Five Freedom framework, it is clear that a lack of nutrients and restriction in feed availability and quality, induced by either management decisions, pasture quality, environmental factors such as climate or interactions with other species, is a source of metabolic stress that compromises welfare. At the same time, the impact on welfare of unbalanced nutrition because of lack of diversity or the impact of PSC is unknown. It is also not clear whether incidental restriction and/or augmentation induce stress in livestock grazing on rangelands. Studies to answer this question will need to be able to assess the level of stress of large numbers of animals dispersed in large areas.

In this chapter, we have often said that livestock can be moved to an environment different from that in which they have evolved, thus creating a mismatch between the adaptive capacity and the environmental pressures. However, over the last 15 years numerous studies have shown that experience early in life can cause epigenetic changes that influence foraging behaviour, habitat selection, and animal health (Provenza 2008). For example, lambs exposed to a high-sodium-containing shrub during uterine life grow faster and handle a salt load better than lambs from mothers on pasture (Chadwick et al. 2009). Epigenetic effects suggest that future generations of livestock could be better adapted to the environment than their parents, and that experience has the potential to improve nutrition and welfare in the same habitat. To take full advantage of these rapid adaptive processes, we need to understand how important early life experiences are in the adaptation of an animal to low-quality diets and/or harsh environments. Should we change the environment in order to increase animal productivity and welfare, or shape an animal (i.e. through experiences in utero and early in life) to better fit its environment?

Livestock that graze in extensive systems are generalist herbivores, meaning that they evolved consuming diverse diets as opposed to monotonous pastures. Single foods generate orosensorial and postingestive signals that cause animals to satiate (Rolls 1986), and satiety may be aversive (Provenza 1996; Provenza and Villalba 2006). In addition, diverse diets increase the likelihood of ingesting beneficial chemicals that enhance the health and welfare of animals (Villalba et al. 2010a). However, the effects of exposure to low- vs. high-diversity diets on stress, health, and animal welfare are unknown.

The interactions between dispersion, increased grazing time, and the expression of other behaviours need to be explored to understand how grazing in extensive systems can decrease the richness and increase the metabolic cost of natural behaviours. For instance, courtship in free-ranging cattle involves a great deal of interaction between animals (Blockey 1976) that requires time and energy and, therefore, may increase stress and reduce production.

The impact of PSC on animal health, welfare, and productivity is receiving an increasing interest. However, only a few compounds have been studied and we do not know much about the optimal dosage, the efficiency of mixture, or even the amount that is consumed and how PSC are metabolised (Provenza and Villalba 2006). Research on the impact of detoxification pathways on diet selection and energetic costs conducted on possums (e.g. Marsh et al. 2006; Nersesian et al. 2011) and woodrats (e.g. Sorensen et al. 2005) is needed on ungulates grazing on rangelands. New studies should explore the effects of specific compounds, doses, and interactions, particularly in animals grazing in extensive systems where PSC are abundant and diverse. Then, we will be able to minimise the health risks and possibly improve the welfare and productivity of animals grazing in rangelands through better preparation and management of animals. To do so, we need to test and monitor novel plants and new plant varieties using bioassays and with animals under experimental conditions prior to them being introduced into grazing systems (Revell and Revell 2007). In addition to these direct effects of PSC on animal health, we need to quantify the metabolic cost associated with the neutralisation/detoxification of PSC by herbivores as well as to explore their ability to select diets that meet their nutritional requirements, while avoiding intoxication by PSC (Jensen et al. 2015).

While ambient conditions above and below the thermoneutral zone are described as heat and cold stress, the relationship between imposed thermal stress and animal welfare is more complex than simply assuming that thermal stress causes decreased welfare. The complexity of the adaptive response of herbivores to extreme temperature under extensive system conditions and the importance of breed on the long-term adaptation to climate change are poorly understood.

The long-term effects of a particular management regime need to be evaluated in order to better predict the nutrition and welfare of animals in the long run. For instance, supplementation programs at high stocking densities may be beneficial for animals in the short run. However, the negative long-term effects on rangelands due to overgrazing will certainly impact the nutrition and welfare of animals in the future.

7.8 Conclusions

Many of the challenges described in this chapter are rooted in the variability and unpredictability of the environment. Foods, habitats, and environmental conditions are not ‘provided’ by the manager, but they occur naturally. The challenge for managers is to provide the conditions and flexibility in their operations that allow animals to express their behaviour and cope with challenges in a way that production and welfare are maximised given the constraints imposed by the ever-changing environmental conditions.

The environmental challenges that animals experience in extensive conditions may represent a source of ‘positive stress’ if animals possess the experience and resources to effectively solve the problems with which they are presented (Meehan and Mench 2007). Thus, some of the challenges that herbivores experience in extensive conditions may become opportunities for managers to create innovative programs that provide animals the training and resources to rectify their states of unbalance, which will ultimately enrich the environment where animals live.