Insights into assessment of the welfare of laying hens in Australia

I. INTRODUCTION

In Australia, the National Animal Welfare Research Development and Extension (RD&E) Strategy is a cross-sectoral strategy under the National Agricultural RD&E Framework. Each of the livestock industries in Australia, including the egg industry, is represented by this National Strategy, which is active in identifying the key areas of importance for the welfare of livestock. Over the last four to five years, in particular, this National Strategy has consistently identified assessment of animal welfare as a critical area of research pursuit. This includes laying hens. Therefore, the focus of this review will be the development of the means to assess the welfare of laying hens.

II. THE IMPORTANCE OF ASSESSING ANIMAL WELFARE

A robust and practical means of assessing animal welfare is paramount in order to develop the means to improve welfare and to demonstrate this improvement. These are now accepted objectives of the livestock industries globally which are striving to continuously improve the welfare of their animals. This is a direct result of increased public awareness and concern over animal welfare. The livelihoods of producers and processors can be dramatically and catastrophically altered by rapid social media-induced changes in consumer behaviour. The significance of this risk is very real. Indeed, a recent economic appraisal of the Australian red meat industries showed that there is no greater risk currently facing the red meat industries in Australia than that of not engaging in animal welfare research and development (MISP, 2015). A similar economic appraisal has not been conducted for the poultry industries; nonetheless, it is clear that the need to demonstrate acceptable levels of welfare, at least, is necessary for community acceptance of egg and chicken meat production.

In addition to the demand of society to improve welfare, there is often a general acceptance that improving animal welfare will improve productivity from animals but there is remarkably little quantitative evidence to demonstrate a causal relationship between welfare and level and quality of productivity. There are many examples in the literature where there are relationships between various measures of welfare and productivity but the causal element is frequently inconclusive or absent and the benefits of improving welfare in economic terms have rarely been addressed. Nevertheless, in a recent comprehensive review it was clearly articulated that there are financial benefits of good animal welfare (Dawkins, 2016). Furthermore, we demonstrated that optimizing floor space and the design features of pens for sows improves welfare with likely improvement in productivity (Hemsworth et al., 2013; Hemsworth et al., 2015).

Certainly, if welfare is poor, productivity can be impacted and this may well be reason alone to ensure that there is appropriate investment to improve animal welfare. A pertinent example of this is feather pecking in laying hens, which is a major negative welfare situation (Glatz, 2000; Ru and Glatz, 2000; Glatz, 2001; Glatz, 2005; Cronin et al., 2014). Feather pecking can result in pain and threats to pecked birds and can result in decreased feed conversion leading to poor feathering (Glatz, 2001). This can result in an increase of 7-12% in the cost of egg production (Glatz, 2001). Furthermore, if the feather pecking develops into cannibalism it can lead to mortalities as high a 25-30% of the flock (Glatz 2001; Cronin et al. 2014). The application of beak trimming can reduce this with savings of up to $AUD240,000 for a flock of 100,000 birds (Glatz and Hinch, 2008) but beak trimming itself presents as a controversial welfare issue (Glatz, 2000; Ru and Glatz, 2000; Glatz, 2005; Cronin et al., 2014). This is clearly an area requiring further investigation.

Irrespective of the relationships or otherwise between improved welfare and productivity, it is clear that the Australian egg industry, like other livestock industries in Australia, must strive to improve the welfare of their hens to ensure protection of the market and a social licence to operate. This requires the robust and practical means to assess the welfare of hens.

III. THE NEED TO DEFINE ANIMAL WELFARE

A universally accepted definition of animal welfare is essential in order to develop methods to assess the welfare of animals. The acceptance of such a definition has proved a major challenge in animal welfare science. Various approaches have been presented to define the welfare of animals including, although not limited to, the “five domains” model (Mellor and Reid, 1994; Fraser et al., 2013; Beausoleil and Mellor, 2015; Beausoleil and Mellor, 2015; Mellor, 2016), the “two question” approach to defining good welfare (Dawkins, 2008, 2016), the Welfare Quality Project (European Union; http://www.animalwelfareplatform.eu/Welfare-Quality-project.php), the biological functioning, affective states and natural living frameworks of animal welfare and the concept that animals have “lives worth living” (Green and Mellor, 2011; Mellor, 2016). Of the definitions developed, we have contended that the most useful in terms of understanding, and thereby assessing, animal welfare are the biological functioning and affective states frameworks (Hemsworth et al., 2015; Tilbrook and Ralph, 2017a,b). The biological functioning framework refers to biological activity that is required to allow an animal to cope with a challenge and adapt to its environment. The biological activity can be extensive, involving many physiological systems and behavioural responses. The affective states framework considers the capacity of an animal to have emotional experiences and how these influence its welfare.

The biological functioning and affective states frameworks each have limitations (for details see Hemsworth et al., 2015) especially if considered in isolation of each other. Consequently, we have suggested that the biological functioning and affective states frameworks should be integrated (Hemsworth et al., 2015) and we have discussed the value of integrating these frameworks in understanding the welfare of group-housed sows (Hemsworth et al., 2015). There is now opportunity to extend this approach to assessment of the welfare of hens. This will require determining how these frameworks are related and where they intersect with respect to the welfare of hens.

IV. THE CONTINUUM OF ANIMAL WELFARE

Since the assessment of animal welfare cannot afford to deal with the biological functioning and affective states in isolation, the development of practical measures of physiological, behavioural and emotional functioning is essential. Importantly, there is a continuum of levels of welfare of animals that ranges from negative to positive (Mellor, 2012; Fraser et al., 2013; Hemsworth et al., 2015; Mellor, 2015, 2016; Tilbrook and Ralph, 2017a) so methods of assessment of animal welfare must be able to provide critical information about the welfare of animals throughout this continuum of welfare. It is now recognised that the continuous improvement of animal welfare requires the ability to move animals from the negative to the positive regions of the welfare continuum. In other words, the ultimate goal is to provide animals with positive states of welfare. This includes laying hens.

V. ASSESSING HEN WELFARE

The continuous improvement of the welfare of hens is dependent on the ability to rigorously assess their welfare in the field. This includes all housing systems in which hens are kept, including cages, barns and free-range systems. As indicated, an assessment tool, or index of welfare, will necessarily be comprised of a range of physiological, behavioural and affective parameters. Presently, no welfare assessment tool exists for laying hens and there is a need to identify the relevant parameters, or biomarkers, of welfare. This is required before it will be possible to implement strategies to improve the welfare of laying hens in the field. This is an area requiring a substantial research effort.

We have recently extensively reviewed the assessment of animal welfare with a focus on mammalian livestock species (Hemsworth et al., 2015; Ralph and Tilbrook, 2016; Tilbrook and Ralph, 2017a,b). Development of the methods of assessment of animal welfare requires the use of multiple indicators from multiple disciplines (Hemsworth et al., 2015; Ralph and Tilbrook, 2016; Tilbrook and Ralph, 2017a,b). Consequently, our approach in mammals is to take a multidisciplinary approach to develop the means to understand both the biological functioning (physiology and behaviour) and affective (emotional) states of animals throughout the supply chain (Tilbrook and Ralph, 2017a). In addition to a scientific approach, we believe that a critical feature to achieving improved animal welfare is to engage with the entire value chain, which includes the public, consumers, processors, retailors, producers and accreditors (Tilbrook and Ralph, 2017a). Our research with cattle, sheep and pigs utilizes novel scientific and technological approaches to provide the practical means to assess physiological, behavioural and emotional functioning under extensive and intensive conditions. The ultimate objective is to develop a suite of measures that will provide a robust and repeatable means to assess animal welfare in practice (Tilbrook and Ralph, 2017a). We believe that a similar approach is required for laying hens. This approach must include practical measures of both biological functioning and affective states as well as an integration of these measures. Below, we briefly outline some of the measures being considered in mammals and challenge that a similar research pursuit be undertaken in laying hens.

a) Biological functioning

Assessment of biological functioning involves quantifying biological activity. Many measures have been undertaken to understand biological functioning, such as measures of the physiological systems that are activated to allow an animal to adapt to, and cope with, its environment. These include body repair systems, immunological defences and physiological stress responses, as well as a variety of behavioural responses (Tilbrook and Ralph, 2017a,b). A large range of behavioural measures have been used in many species, including laying hens, that include stereotypies, redirected behaviours, fearfulness, aggression and displacement activities, amongst others (Hemsworth et al., 2015). One of the most common approaches to assessing biological functioning is quantification of front-line physiological stress systems, such as the hypothalamo-pituitary adrenal (HPA) axis. Recently, we have critically assessed a range of measures used to assess biological functioning, including the HPA axis, in terms of their value in assessing animal welfare (Ralph and Tilbrook, 2016; Tilbrook and Ralph, 2017a,b). It is clear that the physiological responses to challenges are complex and varied, which can make interpretations of the impact of these responses on animal welfare difficult (Ralph and Tilbrook, 2016; Tilbrook and Ralph, 2017a,b).

With respect to stress responses, it is appreciated that there is not always a clear relationship between acute stress and welfare (Ralph and Tilbrook, 2016; Tilbrook and Ralph, 2017). Nevertheless, the reality is that chronic stress, or repeated ongoing stress, almost always has detrimental effects on the normal functioning of animals (Turner et al., 2011; Ralph and Tilbrook, 2016; Tilbrook and Ralph, 2017b) thereby impacting their welfare. Consequently, the development of indexes of welfare must include quantification of stress responses in addition to a range of other physiological, behavioural and affective (see below) measures. Importantly, for these measures to be useful in the assessment of welfare they need to reflect sustained changes over time because chronic activation of stress systems, such as the HPA axis, is when welfare is most likely to be impacted. In mammals, measurement of stress hormones, such as the glucocorticoid cortisol, in hair and wool provide a chronic date stamp of adrenal activity (Burnard et al., 2017) which can be useful in developing an index of welfare when combined with other measures of biological functioning and affective state. In hens, an obvious medium to consider to obtain chronic measures of HPA axis activity is the feather. Indeed, measurement of the principal glucocorticoid in avian species, corticosterone, has been shown to provide a long-term integrated measure of stress physiology in red-legged partridges (Bortolotti et al., 2008), Clark’s nutrackers (Fairhurst et al., 2011) and broilers (Carbajal et al., 2014). Moreover, administration of corticosterone to European starlings resulted in increased concentrations in feathers (Lattin et al., 2011). Studies such as these are lacking in the laying hen, although recently we have been investigating the value of measuring corticosterone in secretions of the uropygial gland (C. de Koning, K. Drake, R. Barekatain, C. Ralph and R Hughes, unpublished) and excreta (C. de Koning, E. Narayan, R. Barekatain, R Hughes and C Ralph, unpublished) from chickens.

It is important to re-emphasise that chronic measures of stress need to be put into the appropriate context when attempting to assess the welfare of hens. On their own, they may be of little value and it is crucial that they are integrated with other physiological (as mentioned above) and behavioural measures, as well as with measures of affective states.

b) Affective states

In comparison to biological functioning, it was long considered that assessing emotions was virtually impossible but this belief is now uncommon and a variety of approaches has been undertaken to quantify affective states. Most of these have been behavioural approaches, with one of the most common being research that investigates the choices that animals make for a chosen environmental option or motivation to perform a type of behaviour (for review see Hemsworth et al., 2015). The premise underlying this approach is that animals will make choices that are in their best interest (Fraser and Nicol, 2011). Other approaches to assessing affective states include measures of behaviour and cognitive bias (Boissy et al., 2007; Mendl et al., 2009) and Qualitative Behavioural Assessment, which uses the intuitive perception of human observers (Wemelsfelder and Mullan, 2014). As intimated above, many of these measures are limited by not taking account of biological functioning. Furthermore, most approaches to measure emotions have focussed on assessing negative affective states and there is a need to be able to measure positive affective states, consistent with the desire to not simply mitigate against poor animal welfare, but to strive for positive animal welfare. In other words, to move animals along the welfare continuum.

Recently, we emphasised the importance of the brain in controlling affective states and proposed that an understanding can be gained from biomedical science to help understand affective function in animals (Tilbrook and Ralph, 2017a). It has been shown, primarily with rodents, sheep and primates, that there are measurable changes in defined regions of the brain that indicate the affective state of an animal (Bergholm et al., 1984). While there have been various studies on regions of the brain and neurophysiological systems in various avian species (e.g. O'Connell and Hofmann, 2011, 2012; Riters et al., 2014; Cordes et al., 2015) there have not been specific attempts to identify these in laying hens with respect to affective states that may impact welfare. This is an area requiring research.

Our recent review detailed the regions of the brain, and the key neural pathways and neurotransmitters that regulate positive and negative affective states (Tilbrook and Ralph, 2017a). The knowledge on this in mammals is extensive. The research effort that has been undertaken in mammalian livestock is now required in laying hens in order to understand affective states to the point where they can be manipulated to induce positive affective states. A primary objective must be to develop procedures to assess the welfare of hens by identifying the neural pathways that generate key emotions, such as reward, fear and pain, and then by developing the means to determine the activity of these pathways.

We have put forward the thesis that candidates for biomarkers of central neuronal activity, among others, may be specific micro RNA’s (miRNAs) that are expressed in response to the activation of various neuronal systems (Tilbrook and Ralph, 2017a). In various mammalian species, these miRNA’s have been measured as signals (biomarkers) of the activation of regions of the brain and neurophysiological systems associated with various affective states (Tilbrook and Ralph 2017a). We are currently undertaking research in this in pigs (L. Marsh, A. Tilbrook, S. Hiendleder and C Ralph, unpublished). It is unknown if miRNAs may also be a biomarker of affective states in hens, but the possibility that they may be surely makes this an enticing area to pursue.

VI. PRACTICAL ASSESSMENT OF HEN WELFARE

Fundamental research is required to develop a suite of measures that can be used to develop a comprehensive assessment of the welfare of hens in practice, both on farm and when spent. Currently, there is insufficient knowledge to develop such an index of the welfare of hens. Biomarkers of biological functioning and affective states are required that can be easily applied in the field. There are clearly some promising candidates for assessing biological functioning, such as targeted measures from feathers (see above). Candidates to assess affective states in laying hens are less obvious and this underscores the need for research in this area. While miRNA’s appear promising candidates in this domain in mammals, the opportunities in laying hens are unexplored. Ultimately, there is requirement for the identification and development of biomarkers of affective state in laying hens that can be applied in the field. This is will be a challenging but important area of research.

VII. CONCLUSION

There is a need to develop reliable practical means to assess the welfare of animals, including hens. This is crucial in order to improve welfare and to demonstrate this improvement, a need that has been largely driven by increased public awareness and concern over animal welfare. While addressing this concern should be a priority of the Australian egg industry, improving animal welfare will likely result in increased consumer recognition of the industry, increased ethical production of high quality safe eggs, market protection and, in some cases, improved production.

Research is necessary to develop a suite of measures that will provide robust and repeatable measures of the welfare of hens. The approach must be multidisciplinary and multifaceted and must encompass measures of physiology, neurophysiology, behaviour and emotions (affect). The assessment of the welfare of hens must extend throughout the supply chain and the research effort should include engagement with the entire value chain, which includes the public, consumers, processors, retailers, producers and accreditors.

Presented at the 29th Annual Australian Poultry Science Symposium 2018. For information on the latest and future editions, click here.