Balancing the animal welfare, farm profitability, human health and environmental outcomes of sheep ectoparasite control in Scottish flocks

Available online at www.sciencedirect.com

Livestock Science 118 (2008) 20 – 33 www.elsevier.com/locate/livsci

Balancing the animal welfare, farm profitability, human health and environmental outcomes of sheep ectoparasite control in Scottish flocks Catherine E. Milne a,⁎, Graham E. Dalton b , Alistair W. Stott a a

Animal Health Economics Team, SAC, Kings Buildings, West Mains Road, Edinburgh, EH9 3JG United Kingdom b Nether Contlaw, Milltimber, Aberdeen, AB13 0ER, United Kingdom Received 29 June 2007; received in revised form 17 January 2008; accepted 19 January 2008

Abstract Controlling external parasites of sheep provides benefits for both animal welfare losses and productivity. However, as control is highly dependent upon the use of veterinary medicines, many of which have potential undesirable side effects for human health and/or the environment, control decisions require the balancing of expected benefits with potential costs. In this paper the decision problem is examined holistically. The method used is a multi-criteria analysis (MCA) in which different weights can be applied to each criterion that affects the decision. This enables an exploration of how changing priorities can influence the ‘best’ course of action. A Scottish context is used though the issues discussed are not unique to Scotland or to the production of sheep. The results highlight the need for a wider thinking and debate on how to identify and agree acceptable solutions to production decisions where undesirable side effects are unavoidable. In addition, the holistic approach provides insights that could be used to identify research priorities and areas where new technological solutions could be particularly valuable. © 2008 Elsevier B.V. All rights reserved. Keywords: Sheep ectoparasites; Regulations; Multi-criteria analysis

1. Introduction There is a diverse set of stakeholders with an interest in the control of external (ecto)parasites of sheep in Scotland. As well as farmers these included water users, wool processors, conservationists, health services, animal welfarists and food consumers. These stakeholders have different viewpoints and priorities. Their opportunities to influence the choice of actions taken by farmers are varied, some have considerable influence and regulations ⁎ Corresponding author. Tel.: +44 131 535 4481; fax: +44 131 535 4345. E-mail address: [email protected] (C.E. Milne). 1871-1413/$ - see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.livsci.2008.01.016

have been enacted supporting their viewpoint. Balancing the views of different stakeholders is problematic for flockmasters and society as a whole and there is no one solution that fully satisfies the goals of all. Sheep farmers have to think about the financial and non-financial sustainability of their business as well as the wider interests of other stakeholders and the biological uncertainties of the ectoparasites that affect their flock. Hitherto, the choices made by flockmasters were heavily influenced by one set of regulations that prescribed actions for the control of sheep scab, one of, if not the most important ectoparasite of sheep in Great Britain (van den Broek and Huntley, 2003). This was

C.E. Milne et al. / Livestock Science 118 (2008) 20–33

due in part to the fact that the prescribed veterinary medicines, which also dominated the market, were broad spectrum and controlled most of the ectoparasites commonly affecting flocks. Relaxation of these regulations in 1992 transferred a greater responsibility for the selection of sheep ectoparasite control measures to farmers. It also permitted a wider range of ectoparasite control medicines with different modes of action and therefore able to target different species of parasite more specifically to gain a share of the market. Many of the medicines that are essential to the control of sheep ectoparasites have the potential to cause harm to human health and/or the environment. In addition, the ectoparasites that can affect sheep include a range of species with distinctive lifecycles and effects on host animals. Hence farmers have had to evaluate the efficacy, likelihood of undesirable side effects and cost:benefit of many more medicines than previously. The ‘best’ medicine for their situation is thus difficult to identify and not always clear cut with the result that the most effective or efficient medicine may not be selected, i.e. there is risk. In this paper, multi-criteria analysis (MCA) is used to examine the problem of sheep ectoparasite control. This method permits alternative priorities for the four main decision criteria of farm profitability, animal welfare, human health and environmental protection to be explored. A holistic or systems approach is increasingly being used in studies to provide insights into likely responses that will occur in interactive situations. Such outcomes are important in setting policy and research priorities. This paper highlights the decision dilemmas faced by sheep farmers in undertaking a single operation on the farm. A Scottish context is assumed for estimation of productivity, flock size and ectoparasite prevalence in the analysis. The issues discussed are not unique to Scotland or to the production of sheep. Other decision choices where undesirable consequences or where risks are unavoidable can be identified in Great Britain and other countries. 2. Sheep ectoparasites and determining the ‘best’ control strategy in Scottish flocks The six ectoparasites of Scottish sheep flocks are scab (Psoroptes communis ovis), lice (mainly Bovicola ovis), keds (Melophagus ovinus), ticks (Ixodes ricinus), headfly (Hydrotoea irritans) and blowfly (Lucilia sericata) (Cawley, 1995; Henderson, 1990). Each has a distinctive lifecycle, affects its host in a different way and occurs independently, hence they can occur singly or in combination on a single host sheep. Detailed descriptions of the lifecycles of these parasites and their effect

21

on hosts have been provided by Urquhart et al. (1996) and Radostits et al. (1997). An understanding of the lifecycle is important as it affects the choice of an appropriate control regime. One important characteristic relevant to their control is whether they are obligate parasites (scab, lice and keds) or non-obligate parasites (ticks, blowfly and headfly). Obligate parasites affect flocks throughout the year and are primarily transmitted via direct contact with infested stock, hence they are most commonly introduced by replacement sheep entering the flock. Non-obligate parasites complete part of their lifecycle off-host, only affecting flocks seasonally from spring to autumn. The grazing environment is thus implicated in the risk of their occurrence. For all stakeholders the control of sheep ectoparasites is desirable for both economic and ethical reasons as they cause losses to both animal productivity and welfare. Effective control of all six ectoparasites is highly dependent upon the application of veterinary medicines (Taylor, 2001). For the obligate parasites, control also requires that only clean animals are transferred between flocks and treatments between neighbouring flocks are co-ordinated to prevent cycling of the disease. In the case of sheep scab all three of these actions have at some time been supported by policy through a series of regulations beginning in 1869 (Spence, 1951). In addition for a period in the late 20th century policy makers ‘approved’ the medicines to be used for scab control. The ‘approved’ medicines co-incidentally were highly effective in the control of many of the other common ectoparasites (Cawley, 1995; Lewis, 1997; VMD, 1999) and thus became the dominant treatments. As a consequence the choice of control strategy was relatively simple up to 1992 with a number of key decisions, or elements thereof, prescribed in the regulations. Since 1992 there has only been a requirement to treat and not to move visibly affected sheep within the regulations (MAFF, 1997). Medicines used to control ectoparasites must be licensed by the Veterinary Medicines Directorate in accordance with EU and UK legislation, but in the case of sheep scab they no longer need to be ‘approved’ and the range of ectoparasite control medicines has increased. Thus regulations now determine fewer of the key sheep ectoparasite control decisions. Over this time period farmers and the wider public have developed a greater awareness of and level of concern about the potential undesirable side-effects to human health and/or the environment of many of the medicines used to control sheep ectoparasites. Increasing sets of regulations have been enacted to protect human health and the environment (HMSO, 1998; HSE, 2002). These regulations have impacted upon sheep

22

C.E. Milne et al. / Livestock Science 118 (2008) 20–33

ectoparasite control decisions while focusing on single issues, as do the regulations that set out minimum standards for animal welfare (HMSO, 2000a,b). They thus provide little decision support to farmers because they fail to recognise the interactions between different medicines and their varying effects on animal welfare, human health and the environment. As a consequence individual farmers must weigh the risks and potential costs against the likely benefits of using any one medicine. These are not clear-cut and have interactive side effects. 3. A multi-criteria analysis of sheep ectoparasite control A holistic analysis of the effects of ectoparasite control decisions is necessary because of the existence of multiple outcomes for each alternative medicine. Decisions with multiple consequences or outcomes can be evaluated holistically by multi-criteria analysis (MCA) or multiattribute analysis (DTLR, 2003). MCA typically derives a performance matrix, where the decision criteria form the columns and the choice alternatives form the rows. Each criterion may be allocated a weight with regard to its importance to the final decision choice. The consequences, or performance outcomes, for each alternative are then appraised by criterion to provide qualitative or quantitative information within the matrix. Different scales may be used for each criterion and the performance outcomes may be recorded non-numerically, for example with regard to environmental harm. Converting the information gathered in the matrix into a single common scale allows the identification of the most preferred action across all criteria. Scores are allocated within a criterion to the performance of alternative options according to a strength of preference (i.e. alternatives are scores within a column). A total score can thus be derived for each alternative by summing the weighted scores for each criterion.

considered ‘fair’, and provides a baseline for comparison. • Case 2 represents a situation in which human health and the environment have a lower weighting than animal welfare and farm profitability. This case is indicative of the guidance given to farmers by regulations 15–20years ago in Great Britain when the required actions for the control of scab were greater and the human and/or environmental side-effects of ectoparasiticides were subject to fewer controls. For investigative purposes, as there was no objective data to indicate an appropriate level for the lower weightings, a weight of 0.5 has been adopted for human health and environmental criteria relative to 1.0 for the farm profitability and animal welfare criteria. Whilst a group of stakeholders could have been established and asked to state the weightings they considered appropriate, these would only have been applicable to this group and would not necessarily be representative of other groups or individuals. The alternative weightings that would then have been derived would thus have been no more or less appropriate than those chosen above to explore the problem of sheep ectoparasite control. 3.2. Alternative options

The four criteria identified as important in the selection of sheep ectoparasite control measures were farm profitability; animal welfare; human health; and the environment. The actual weight that should be given to each was not known and will vary across different groups in society. To test the overall acceptability of the respective control measures two possible sets of weights (cases) were used as defined below.

The alternative options for ectoparasite control strategies form the rows for the matrix. These were made up of a sequence of two treatments over the period of a production cycle, or one year. This is a simplification of the real situation but coincides with the peak periods when ectoparasites affect Scottish flocks. The target parasites were assumed to be scab, lice, ticks and blowfly. Keds were excluded because currently they are not widespread in the national flock, headfly are excluded as their control decision is normally separate from that of the other parasites for medicinal (treatment area, medicine efficacy and/or dosage) reasons (Henderson, 1990; VMD, 2000). The first treatment takes place in the autumn at the start of the production cycle. At this time the focus is on the obligate parasites, scab and lice, that may be introduced to the flock with replacements and ticks. The second treatment, applied in spring–summer, aims to control the non-obligate parasites occurring during this period, namely ticks and blowfly. Five alternative medicines have been selected for inclusion in the MCA:

• Case 1 demonstrates a situation in which each criterion has an equal weight, based on the assumption that no information exists. This might be

(i) Organophosphate (OP) based dip (diazinon) (ii) Synthetic pyrethroid (SP) based dip (High cis cypermethrin)

3.1. Decision criteria and relative weightings

C.E. Milne et al. / Livestock Science 118 (2008) 20–33

23

inferences should be drawn regarding medicines not included in this analysis other than that they were deemed to be outside the brief of this paper of balancing conflicting objectives. It should be noted that the individual products available to farmers change over time in response to technological developments, pesticide resistance, and product licenses in association with government interventions such as the temporary suspension of products from the market. This has happened twice in recent years, firstly with the temporary removal of organophosphate dips in 1999 and in 2006 with the temporary suspension of SP dips (Anderson, 2001; FitzGerald, 2006). Sheep production systems in Scotland are varied in nature and as shown previously by Milne et al. (2007) the profit maximising course of action may not be constant for all flocks. Two flock types/sizes were therefore investigated in this study; a 1000 ewe hill flock and 100 ewe lowground flock. The hill flock was assumed to be at risk of tick infestation whilst the lowground flock was not due to differences in their grazing environment. Productivity levels were assumed to be higher in the lowground flock by comparison to the hill flock. The two flock types/sizes used in this study represent the two extremes of Scottish sheep production systems encompassing a range of variables that may influence the decision choice on a particular farm.

(iii) Synthetic pyrethroid (SP) pour-on (cypermethrin) (iv) Insect growth regulator (IGR) pour-on (cyromazine) (v) Injectable macrocyclic lactone (ML) (doramectin) The spectrum of ectoparasites controlled by each of these five medicines is shown in Table 1. Their efficacy in practice for any individual flock is uncertain as it will vary with a number of factors including the efficacy of the medicine itself, how well it is applied, and climatic conditions during and subsequent to application. A precise and detailed estimate of medicine efficacy would not provide a greater insight into the problem of balancing multiple and conflicting objectives, which is the purpose of this paper. Moreover, the perception of many farmers is that scab medicines are of equal efficacy (Clark and Milne, 2003) and whilst this may be incorrect it is what influences their actual behaviour. Based on the medicine efficacy and target ectoparasites 16 alternative control strategies were identified as shown in Fig. 1. Medicine (iv), the insect growth regulator cyromazine, has not been included as an alternative at the autumn treatment since it is only effective for blowfly prevention and this is not one of the target parasites at this time period. Similarly while medicine (v), the injectable macrocyclic lactone doramectin is only effective against one of the target parasites, sheep scab, which only occurs in the autumn time period of the model it has been excluded as a spring/summer control alternative. The medicines selected for inclusion in this study incorporate a range of active ingredients and application methods that can determine the outcome. The method of application has important implications for labour and facilities and so the financial outcome. In the case of dips there is also ‘spent’ or waste dip to be disposed of and hence particular environmental implications. No

3.3. Scoring of alternatives A common scoring system was adopted in this study to permit a numeric holistic analysis of the 16 choice alternatives. A score of zero was given within each criterion for treatments where there was no expected loss/ potential harm to the environment or human health and the minimum loss to farm profitability and animal welfare. This was the alternative that maximises the

Table 1 Medicines authorised for the control of sheep ectoparasites in Great Britain Medicines

Scab

Lice

Keds

Ticks

Headfly

Blowfly control

Blowfly-Prevention

Dips: Organophosphate (OP) Synthetic pyrethroid (SP): High cis cypermethrin ⁎

✓ ✓

✓ ✓

✓ x

✓ ✓

x x

✓ ✓

✓ x

Pour-ons Synthetic pyrethroid (SP): Cypermethrin Insect growth regulator (IGR): Cyromazine

x x

✓ x

x x

✓ x

✓ x

✓ x

✓ ✓

Injectables Macrocyclic lactone (ML): Doramectin

✓

x

x

x

x

x

x

⁎In some formulations, blowfly strike will also be prevented. Note: All data are correct at the time of preparation to the best knowledge of the authors but product data should be checked prior to usage (VMD, 2005).

24

C.E. Milne et al. / Livestock Science 118 (2008) 20–33

Fig. 1. Alternative control strategies (adapted from Milne et al., 2007).

avoidable disease losses, as defined by McInerney (1996). The treatment that would give rise to the greatest expected losses/potential harm was allocated a score of − 1 with the remaining treatments scored relative to these two points. As each alternative control strategy consists of two treatments the final scale for each criterion was between zero to − 2. 3.3.1. Farm profitability scores Previously Milne et al. (2007) constructed a decisiontree model to determine the profit-maximising ectoparasite control strategy for different flock types in Scotland. This simplified representation of the decision problem

encompasses time and risk. Both of which are key to the expected financial outcome of alternative courses of action. The decision tree model was used to estimate the expected financial outcome of the alternative control strategies for the two flock types/sizes considered in this study. Each expected value was the sum of the probability weighted outcomes for a particular control strategy and so takes account of the chance or risk that an ectoparasite will affect the flock and be controlled by the medicine applied. The financial results are shown in Tables 2 and 3 for Case 1 and 2 respectively along with the relative scores that were derived from them. The expected financial results include estimated values of any disease

C.E. Milne et al. / Livestock Science 118 (2008) 20–33

25

Table 2 Case 1 1: Farm profitability scores for alternative control strategies including costs of compliance with regulations applicable in 2005 Control strategy

Autumn medicine

Spring/ summer medicine

1000-ewe hill flock

100-ewe lowground flock

Expected value £

Farm profitability score

Expected value £

Farm profitability score

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

OP dip OP dip OP dip OP dip SP dip SP dip SP dip SP dip SP pour-on SP pour-on SP pour-on SP pour-on ML injectable ML injectable ML injectable ML injectable

OP dip SP dip SP pour-on IGR pour-on OP dip SP dip SP pour-on IGR pour-on OP dip SP dip SP pour-on IGR pour- on OP dip SP dip SP pour-on IGR pour-on

−1438 −1818 −1878 −4868 −1852 −2232 −2292 −5282 −2628 −3008 −2759 −5749 −3726 −4106 −3857 −6847

0.00 −0.14 −0.16 −1.27 −0.15 −0.29 −0.32 −1.42 −0.44 −0.58 −0.49 −1.59 −0.85 −0.99 −0.89 −2.00

− 399 − 437 − 443 − 457 − 439 − 477 − 483 − 497 − 492 − 530 − 227 − 241 − 571 − 609 − 306 − 320

− 0.90 − 1.10 − 1.13 − 1.20 − 1.11 − 1.31 − 1.34 − 1.42 − 1.39 − 1.59 0.00 − 0.07 − 1.80 − 2.00 − 0.41 − 0.49

OP = Organophosphate. SP = Synthetic pyrethroid. IGR = Insect growth regulator. ML = Macrocyclic lactone. 1 Case 1: all criteria have an equal weighting.

losses as well as control costs including compliance with regulations, labour, medicines and fixed items such as dipping baths. 3.3.2. Animal welfare scores The irritation, pain and distress that ectoparasites can inflict upon host animals either directly, or, in the case of

ticks, as a consequence of the infectious diseases they transmit can be severe. Sheep scab has been cited as the greatest threat to sheep health and welfare in Great Britain (Lewis, 1997) and in Great Britain infestations must be controlled by law (MAFF, 1997). The mites that cause sheep scab are obligate parasites whose faeces set up an allergic reaction on the skin that causes extreme

Table 3 Case 2 2: Farm profitability scores for alternative control strategies, assuming regulatory conditions as applicable 15–20 years ago Control strategy

Autumn medicine

Spring/ summer medicine

1000-ewe hill flock Expected value £

Farm profitability score

Expected value £

Farm profitability score

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

OP dip OP dip OP dip OP dip SP dip SP dip SP dip SP dip SP pour-on SP pour-on SP pour-on SP pour-on ML injectable ML injectable ML injectable ML injectable

OP dip SP dip SP pour-on IGR pour-on OP dip SP dip SP pour-on IGR pour-on OP dip SP dip SP pour-on IGR pour-on OP dip SP dip SP pour-on IGR pour-on

−1281 −1661 −1721 − 4711 −1695 −2075 −2135 −5125 −2470 −2850 −2759 −5749 −3569 −3949 −3857 −6847

0.00 − 0.14 − 0.16 − 1.23 − 0.15 − 0.29 − 0.31 − 1.38 − 0.43 − 0.56 − 0.53 − 1.61 − 0.82 − 0.96 − 0.93 − 2.00

− 241 − 279 − 285 − 299 − 282 − 320 − 326 − 340 − 334 − 372 − 227 − 241 − 413 − 451 − 306 − 320

− 0.13 − 0.47 − 0.52 − 0.65 − 0.49 − 0.83 − 0.88 − 1.00 − 0.96 − 1.30 0.00 − 0.12 − 1.66 − 2.00 − 0.70 − 0.83

2

100-ewe lowground flock

Case 2: Animal welfare and farm profitability have a weighting of 0.5 whilst the environment and human health have weightings of 1.

26

C.E. Milne et al. / Livestock Science 118 (2008) 20–33

irritation. Affected stock scratch themselves on any available object, their appetite is suppressed and mortality is common, though typically caused by secondary infections, emaciation and dehydration (Bates, 1997, 1999; Corke and Broom, 1999; Parker et al., 1999). In a survey of Scottish farmers blowfly was identified as the second most important ectoparasite of sheep after scab (Milne et al., 2007). Adult females lay their eggs on the fleece of host sheep, the maggots which hatch 2–3days later secrete an enzyme that liquefies the skin and flesh of hosts, providing a ‘soup’ on which they can feed (Tellam and Bowles, 1997; Urquhart et al., 1996). As with scab, the pain and distress to affected stock is commonly severe and in England and Wales alone an estimate 12,000 sheep die from blowfly strike each year (French et al., 1995). In hill and upland areas ticks may also affect sheep. This parasite requires one blood meal per annum from a host animal and moist, sheltered vegetation to survive over the remainder of the year. Their importance is as disease vectors for although many ticks may infest a sheep, anaemia is rare. The diseases they transmit in Great Britain include louping-ill, tick-borne fever and tick pyaemia resulting in abscesses typically in joints, fevers, meningo-encephalomyelitis, and impairment of the host's immune system (Brodie et al., 1986; Henderson, 1990; Urquhart et al., 1996). Effective control measures for these three and other ectoparasites can thus provide great benefits to the welfare of sheep, particularly preventative measures as these will maximise animal welfare. There is no agreed measure for the welfare impact of sheep ectoparasites. In some studies it has been found that there is a close link between animal productivity

and the perceived welfare impact (Dwyer, 2003; Heath et al., 1987). Production losses, as estimated by the decision tree previously developed by Milne et al. (2007) were therefore used in this study as a proxy for welfare. The estimated production losses of alternative control strategies and the relative scores derived from them are given in Table 4. 3.3.3. Human health scores Whilst there are benefits to human health from the control of ticks as they transmit Lyme's disease which is zoonotic (Joss et al., 2003), human health may be seriously harmed by some of the veterinary medicines used to control sheep ectoparasites. Specifically organophosphate based dips may cause interference with the transmission of nervous impulses in mammals – including humans – as well as in insects (Swanston and Shaw, 1990). Over recent years the level of concern regarding and evidence of damage to human health from organophosphate products has grown. The effects include muscle twitching, cramps, vomiting, salivation and sweating, and in severe cases may cause failure of the muscles used for breathing. In addition chronic effects on cognitive skills have been detected (O'Malley, 1997; Steenland, 1996; Swanston and Shaw, 1990). Although the effects are potentially serious the likelihood of harm is variable. It can be reduced by, for example, the usage of protective clothing and following the discovery that in Great Britain handlers of concentrated sheep dip were at particular risk, packaging of organophosphate dips was modified to minimise operator contact (Anon, 2000; MAFF, 1999a,b). In

Table 4 Animal welfare scores for alternative control strategies estimated from production loss data reported by Milne et al. (2007) Control Strategy

Autumn medicine

Spring/ summer medicine

1000-ewe hill flock Losses £

Animal welfare score⁎

100-ewe lowground flock Losses £

Animal welfare score⁎

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

OP dip OP dip OP dip OP dip SP dip SP dip SP dip SP dip SP pour-on SP pour-on SP pour-on SP pour-on ML injectable ML injectable ML injectable ML injectable

OP dip SP dip SP pour-on IGR pour-on OP dip SP dip SP pour-on IGR pour-on OP dip SP dip SP pour-on IGR pour-on OP dip SP dip SP pour-on IGR pour-on

− 161 − 161 − 161 − 1586 − 173 − 173 − 173 − 1598 − 445 − 445 − 445 − 1870 − 1055 − 1055 − 1055 − 2480

− 0.13 − 0.13 − 0.13 − 1.28 − 0.14 − 0.14 − 0.14 − 1.29 − 0.36 − 0.36 − 0.36 − 1.51 − 0.85 − 0.85 − 0.85 − 2.00

− 14 − 14 − 14 − 14 − 16 − 16 − 16 − 16 − 63 − 63 − 63 − 63 − 136 − 136 − 136 − 136

−0.21 −0.21 −0.21 −0.21 −0.24 −0.24 −0.24 −0.24 −0.93 −0.93 −0.93 −0.93 −2.00 −2.00 −2.00 −2.00

C.E. Milne et al. / Livestock Science 118 (2008) 20–33

addition, in response to concerns about the effects of sheep dip on human health since 1994 purchasers of organophosphate based dips in Great Britain have been required to hold a Certificate of competence in the safe use of sheep dips. This Certificate of competence must now be held by users of any sheep dip (HSE et al., 1999) and a precautionary approach (prevent exposure rather than control exposure) is required under the Control of Substances Hazardous to Health (COSHH) Regulations 2002 (HSE, 2005). In the MCA a score of − 1 was therefore allocated for each treatment of an OP dip and a score of − 2 occurs where both the autumn and spring– summer treatments are OP dip. For the other medicines included in the analysis a score of 0 was given (no loss) at each treatment. 3.3.4. Environment scores Organophosphate, synthetic pyrethroid and macrocyclic lactone based medicines used in the control of sheep ectoparasites all act by interfering with the nervous system. The medicines also affect non-target species (Taylor, 2001), as noted above for OPs and human health. Damage in the aquatic environment, which includes killing of fish and invertebrates, has been the main focus of attention as can occur with the discharge into water courses of run off from the fleece after dipping as well as waste liquor from sheep dips and wool scours. There is a code of practice for sheep dipping and regulations set out minimum standards (SEPA, 2006). Furthermore the Scottish Environmental Protection Agency (SEPA) has a ‘Groundwater Protection Policy’ which adopts a precautionary approach to pollution and aims to ‘protect groundwater quality by minimising the risks posed by point and diffuse sources of pollution’ (SEPA, 2007). As for human health, environmental damage can only arise if contamination occurs, and the greatest risk of this is associated with dips (organophosphate and synthetic pyrethroid) where used, or ‘spent’, liquors need to be disposed of. This is typically done by spreading the dip liquor on land after dilution (Chatfield, 2001; Taylor, 2001). Most recently in Great Britain the severity of damage caused by environmental contamination by synthetic pyrethroid dips has led to their temporary suspension from the market (VMD, 2006). Damage is also known to be caused by contamination of the nonaquatic environment with macrocyclic lactones, which are administered intramuscularly and are excreted in the dung of treated animals (Taylor, 1999). Thus even when used according to recommended guidelines medicines used to control sheep ectoparasites can cause unintended damage. Table 5 shows the scores allocated to each medicine for the MCA and, for example, where SP dips were used at

27

both the autumn and spring–summer treatments a score of − 2 was allocated, that is two treatments with a value of − 1 per treatment. These scores are representative of the relative order of environmental harm that each medicine may cause as insufficient information was available to score them with greater refinement. 4. Results 4.1. Case 1: Each criterion has an equal weighting The MCA results for the hill flock of 1000 ewes, when each of the four criteria were given equal weighting, are shown graphically in Fig. 2. It can be seen from Fig. 2 that the total score varies between control strategies. Strategy 11 was the ‘best’ overall strategy in this MCA having the highest total score. The score of − 0.94 was made up of negative outcomes for animal welfare and farm profitability. Strategy 4 was the worst strategy overall with a total score of − 4.05 with undesirable outcomes across all four criteria. The profit-maximising solution for this flock type/size was Strategy 1 with an OP dip in the autumn and spring/summer that gave a total score of − 3.15. Whilst giving a better animal welfare outcome than Strategy 11, there was a greater potential for harm to both human health and the environment. Adopting Strategy 11, the ‘best’ overall control strategy, in preference to Strategy 1, the profit-maximising strategy, reduces the expected farm profit by £1321 calculated as − £2759 minus − £1438 (see Table 2) or over £1 per ewe. The MCA results shown in Fig. 2 also demonstrated that whilst control strategies can be equal in terms of overall score, they may consist of differing ‘bundles’ of goods. For example, Strategies 12 and 13 had similar total scores, but Strategy 12 incurred costs to farm profitability and animal welfare while Strategy 13 incurred costs across all four criteria. This demonstrates that additional farm profitability and animal welfare costs can be substituted for human health and environmental costs.

Table 5 Environmental scores for alternative medicines applied at each treatment Medicine

Environment score

OP dip SP dip SP pour-on IGR pour-on ML injectable

−0.5 −1 0 0 −0.25

28

C.E. Milne et al. / Livestock Science 118 (2008) 20–33

Fig. 2. Case 1: Total and individual criterion scores for a 1000-ewe hill flock, equal weighting for each consequence and the expected value outcome.

The results of the MCA for the lowground flock of 100 ewes, when each criterion was given an equal weighting, are illustrated in Fig. 3. For the lowground flock, the ‘best’ control strategies from both the private farm business profitability and overall optimal social standpoints concur in Strategy 11. However, Strategy 11 incurs greater animal welfare costs than some other strategies, demonstrating that animal welfare in some situations can be substituted for farm profit, as well as for human health and environmental protection. 4.1. Case 2: Human health and the environment criteria allocated lower weights than animal welfare and farm profitability criteria In this analysis the farm profitability scores given in Table 3.were used to take account of the lower regulatory

costs incurred by 15–20years ago. The results for a hill flock of 1000 ewes are shown in Fig. 4. The control strategies that generated the highest total score and greatest profit respectively were Strategies 11 and 1. This was consistent with the result for Case 1 demonstrating that the greater weighting applied to human health and the environment in this case did not alter the optimal control strategies. For the 1000 ewe hill flock a conflict between the ‘best’ control strategy from private and social standpoints was thus highlighted by the MCA for the two Cases investigated. The results for a 100-ewe lowground flock in the Case 2 scenario are shown in Fig. 5. Strategy 11 still generated the highest total score and farm profit as in Case 1. Thus the ‘best’ control strategy from private and social standpoints concurred with the sole cost being to animal welfare. The weighting adjustment did not alter the ranking of these preferences.

C.E. Milne et al. / Livestock Science 118 (2008) 20–33

29

Fig. 3. Case 1: Total and individual criterion scores for a lowground flock of 100 ewes, equal weighting for each consequence and the expected value outcome.

The rank order of alternative control strategies, according to their total score calculated in the MCA, for the two potential social preferences encompassed by Case 1 and 2, as described above, are summarised in Table 6. As can be seen from Table 6, Strategy 11 was the most preferred strategy across all four Cases: flock type/

sizes investigated indicating a robustness in this strategy. Furthermore it is notable that the two most preferred and two least preferred strategies remain constant by flock type/size across the two Cases. However, the rank order for most strategies does vary between Cases and flock type/size. Referring to Figs. 2–5 it can be seen that for a hill flock of 1000 ewes the

Fig. 4. Case 2: Total and individual criterion scores for a 1000-ewe hill flock, unequal criterion weighting.

30

C.E. Milne et al. / Livestock Science 118 (2008) 20–33

Fig. 5. Case 2: Total and individual criterion scores for a 100-ewe lowground flock, unequal criterion weighting.

tightening of regulations in recent years as illustrated by the different assumptions between Case 1 and 2 shows that Strategy 11 is now a more dominant strategy compared with the next best alternative — Strategy 7. For a lowground flock of 100 ewes the difference between the ‘best’ strategy from a social point of view and the next best strategy is small and has not changed with the revised assumptions. These results highlight that for the hill flock not only is there a conflict between the

Table 6 Rank order of alternative control strategies by flock type/size and Case Rank

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Control strategy number 1000-ewe hill flock

100-ewe lowground flock

Case 1

Case 2

Case 1

Case 2

11 7 15 3 10 9 6 2 5 14 1 12 13 8 16 4

11 7 3 10 6 2 9 5 1 15 14 13 12 8 4 16

11 12 15 16 7 8 3 4 10 6 2 9 5 1 14 13

11 12 3 4 7 8 1 2 5 6 9 15 10 16 13 14

Strategies are coded as per the key provided in Fig. 2.

‘best’ private and social alternative but under current conditions maximising the social benefits is dependent upon a single ectoparasite control strategy. The results demonstrate that there is more flexibility and stability with changing weightings for the lowground flock. 5. Discussion The multi-criteria analysis demonstrated the effect on rank order of alternative strategies from changing the weight allocated to each decision criterion. As noted earlier the actual weights reflecting society's current preferences have not been quantified. This highlights three points, firstly that it is important that agreed weights are established. Some evidence for the weights can be drawn from changes in regulations over time in so far as they have occurred following an informed debate where trade-offs between competing objectives have been balanced out. However, such evidence is of a historic nature and the relative weightings are not explicit. Further studies are necessary to facilitate the expression of preferences by a range of different stakeholders. Secondly that these need to be communicated to all stakeholders including government, consumers and farmers. Thirdly these weights should be incorporated into stakeholder decisions, including the design of policy interventions using the type of methodology advocated in this paper. Without these actions the outcomes of sheep ectoparasite control decisions will remain uncertain. Conflicts between private and social interests will then not be addressed. Moreover, farmers will continue to be faced with a

C.E. Milne et al. / Livestock Science 118 (2008) 20–33

decision choice where it is impossible to satisfy the demands of all external stakeholders and the needs of their business. The scores given to alternative medicines are also an important factor determining the most preferred strategies and their rank order. An understanding of the true impact of each medicine will require further scientific research into the efficacy (including resistance), animal welfare, human health and environmental consequences of ectoparasites and their control. Furthermore the assumed scores were based on the potential for harm if contamination occurs. As such they reflect a precautionary approach as promoted by legislation and legislative bodies in Scotland. It did not take into consideration risk moderating factors as can be present on individual farms, for example the use of protective clothing. Where such actions are implemented the expected harm may be very low and arguably this would be a more appropriate premise on which to evaluate the choice alternatives. For example, if dips did not receive a negative score for human health or the environment it can be seen from Figs. 2–5 that the total scores and preference order would alter considerably. Encouragingly, a number of research studies have recently been tendered that could proffer better information on the potential harmful impacts of medicines used in the control of sheep ectoparasites (DEFRA, 2007). A precautionary approach, which is justified by a lack of knowledge, assumes the worst outcome will occur and overestimates the undesirable impact(s) of an action (Perman et al., 2003). Thus the guidance given by regulations based on this principle is dominated by the worst events irrespective of their likelihood, resulting in sub-optimal choices. The MCA highlights that a risk assessment incorporating both the potential for harm and its likelihood for a range of circumstances is needed to develop the best policy approach and appropriate courses of action. The holistic approach presented in this paper has demonstrated the interactions between the four decision criteria. In doing so it has highlighted the decision dilemma faced by farmers since each solution investigated gives rise to some undesirable consequence(s), which is (are) not apparent if the problem is viewed from a single standpoint. Insights are thus gained into opportunities whereby the private and/or social outcomes of sheep ectoparasite control decisions could be improved. These include the development of new technologies, medicines and disease eradication, control systems including complimentary husbandry, some of which are already subject to current research. For example, research has been undertaken into non-chemical methods of ectopar-

31

asite control including the development of a sheep scab vaccine and reductions of blowfly populations through trapping (Moredun Institute, 2000; Wall et al., 1995). Industry led schemes aimed at reducing the prevalence of sheep scab (Hosie, 2003) have also been initiated with the hope of disease eradication over time, as has been achieved in New Zealand. Development of new veterinary medicines and application methods that are less harmful to human health and/or the environment whilst addressing the practical constraints of sheep farming in extensive systems, could also be of great benefit to the sheep industry and society as a whole. The holistic approach has also shown that trade-offs can be made between the outcomes for different criteria. For example a higher level of environmental protection can be achieved at the cost of animal welfare and farm profitability as shown in Fig. 2 when moving from strategy 1 to strategy 11. Similarly, a higher level of animal welfare can potentially be achieved by adopting a strategy that is more risky to human health as shown in Fig. 2 when moving from strategy 14 to strategy 1. If the precautionary principle is applied in a rigorous manner then trade-offs and more balanced overall solutions are ruled out. The policy approach to undesirable outcomes, potential and expected, thus requires careful and contextual consideration where there are multiple criteria affecting the decision choice. Furthermore, the results show the value of undertaking holistic analyses to fully evaluate the implications of pursuing improvements in any single issue. For example, the temporary suspension of OP dips from the market on human health grounds (VMD, 2001) was certain to have a negative impact on farm profit and animal welfare for a 1000 ewe hill flock (Fig. 2 and Tables 2 and 3), given the score assumptions used in this analysis. This may also be the situation if these medicines become unavailable in the future. Similarly the impact of the temporary suspension of SP dips from the market in 2006 (VMD, 2006) could be examined. A poorer animal welfare outcome is potentially important not only in its own right but due to the greater probability that minimum standards set out in regulations cannot be complied with. 7. Conclusions The final weighted scores generated for each alternative ectoparasite control strategy considered are just some of the possible outcomes from an analysis of the type undertaken here. In order for a realistic MCA to be completed with a degree of accuracy that would enable definitive choices to be made it is necessary that better societal weights are established for each criterion

32

C.E. Milne et al. / Livestock Science 118 (2008) 20–33

and scientifically supported scores for medicines. It should be noted however that criterion weights will change over time as societal preferences are dynamic. The completed MCA demonstrated that each solution incurs undesirable consequences or risks. Identifying and developing new solutions that improve the animal welfare, human health and/or environmental outcomes of sheep ectoparasite control without reducing farm profitability would therefore be highly beneficial. The approach taken has also provided insights into potential research priority areas. The holistic approach has demonstrated that for this decision type, regulations that focus on single issues and adopt the precautionary principle may not give rise to optimal choices for either private individuals or society as a whole. Furthermore the results demonstrate that the effectiveness of policy interventions can be particularly uncertain where a decision problem is multi-faceted, and may be subject to more than one policy measure. In addition, the MCAs have shown that the ‘bundle’ of benefits can vary, and that there can be conflict between outcomes. The ‘best’ course of action is dependent upon the priorities given to each criterion highlighting the need for a wider thinking and debate on how to identify and agree acceptable solutions to production decisions where undesirable side-effects are unavoidable. Finally, as can be seen from the holistic examination, the decision choice is highly complex. Compiling and evaluating all the necessary information is demanding. A decision support tool could therefore be of value, for instance a multi-criteria analysis decision model as developed in this paper. In addition there is a need for better decision support for highly complex decisions such as sheep ectoparasite control. Users will be able to identify other decision choices where trade-offs occur between conflicting outcomes and where a holistic analysis could provide new insights for decision-makers including researchers and policy. Acknowledgement The authors are grateful to SEERAD who sponsored this work and to colleagues at SAC for help and advice and to Prof. K. J. Thomson of Aberdeen University. References Anderson, R., 2001. VMD Annual Report and Accounts 2000/01. http://www.vmd.gov.uk/Publications/AnnReps/vmdanrep01.pdf. Access date 1/5/07. Anon, 2000. Relaunch for OP scab products. http://www.fwi.co.uk/ search.asp?fn=showArchive&redirect=http://www.fwi.co.uk/live/ fweekly/fw101688.htm. Access date 27/1/03.

Bates, P., 1997. The pathogenesis and ageing of sheep scab lesions — part 2. State Veterinary Journal 7, 13–16 MAFF. Bates, P., 1999. A practical guide to the control of sheep scab. The Moredun Foundation. Brodie, T.A., Holmes, P.H., Urquhart, G.M., 1986. Some aspects of tick borne diseases of British sheep. Veterinary Record 118, 415–418. Cawley, G.D., 1995. Ovine Ectoparasites found in the British Isles. The Moredun Foundation News Sheet 2. Chatfield, P., 2001. Sheep Dipping: (PPG12) Pollution prevention guidelines. http://www.environment-agency.gov.uk/commondata/ 105385/ppg12.pdf. Access date 26/9/01. Clark, S., Milne, C., 2003. Ectoparasite awareness in sheep. Veterinary Record 152, 271–272. Corke, M.J., Broom, D.M., 1999. The behaviour of sheep with sheep scab, psoroptes ovis infestation. Veterinary Parasitology 83, 291–300. DEFRA, 2007. Animal Health and Welfare. Research requirements 2008/9. http://www.defra.gov.uk/science/funding/competitions. htm.Access date 27/6/07. DTLR, 2003. DTLR multi-criteria analysis manual. DTLR, London. Dwyer, C., 2003. SAC Personal communication. Edinburgh. FitzGerald, J., 2006. VMD Annual Report and Accounts 2005/6. http://www.vmd.gov.uk/About/ARA0506web/vmdara0506.pdf. Access date1/5/07. French, N.P., Wall, R., Morgan, K.L., 1995. The seasonal pattern of sheep blowfly strike in England and Wales. Medical and Veterinary Entomology 9, 1–8. Heath, A.C.G., Bishop, D.M., Tenquist, J.D., 1987. The effects of artificially-induced fly-strike on food intake and liveweight gain in sheep. New Zealand Veterinary Journal 35, 50–52. Henderson, D.C., 1990. The veterinary book for sheep farmers. Ipswich Farming Press. HMSO, 1998. The Groundwater Regulations 1998. http://www.opsi. gov.uk/SI/si1998/19982746.htm. Access date 22/11/06. HMSO, 2000a. Statutory Instrument 2000 No. 1870: The Welfare of Farmed Animals (England) Regulations 2000. http://www.legislation.hmso.gov.uk/si/si2000/20001870.htm. Access date 14/10/02. HMSO, 2000b. The Welfare of Farmed Animals (Scotland) Regulations 2000. http://www.opsi.gov.uk/legislation/scotland/ssi2000/ 20000442.htm. Access date 22/5/06. Hosie, B., 2003. Scottish Sheep Scab Initiative. http://www1.sac.ac.uk/ vet/external//sheepscabinitiative/default.asp. Access date 10/1/05. HSE, 2002. Health and Safety Regulation: A Short Guide. http://www. hse.gov.uk/pubns/hsc13.htm Access date 14/10/07. HSE, 2005. COSHH: A brief guide to the Regulations (ING136 (rev3)). http://www.hse.gov.uk/pubns/indg136.pdf. Access date 22/5/07. HSE VMD, EA and SEPA, 1999. Sheep Dipping. http://www.hse.gov. uk/pubns/as29.htm. Access date 28/11/06. Joss, A.W.L., Davidson, M.M., Ho-Yen, D.O., Ludbrook, A., 2003. Lyme disease — what is the cost for Scotland? Public Health 117, 264–273. Lewis, C., 1997. Update on sheep scab. In Practice 558–564. MAFF, 1997. The Sheep Scab Order 1997. HMSO. MAFF, 1999a. Government announces four point plan on organophosphates. MAFF. MAFF, 1999b. Research published on effects of exposure to OP sheep dips. Press release. McInerney, J., 1996. Old economics for new problems — livestock disease: Presidential address. Journal of Agricultural Economics 47, 295–314.

C.E. Milne et al. / Livestock Science 118 (2008) 20–33 Milne, C.E., Dalton, G.E., Stott, A.W., 2007. Integrated control strategies for ectoparasites in Scottish sheep flocks. Livestock Science 106, 243–253. Moredun Institute, 2000. Moredun announces sheep scab vaccine hope. More from the Moredun, p. 1. O'Malley, M., 1997. Clinical evaluation of pesticide exposure and poisonings. The Lancet 349, 1161–1166. Parker, L.D., O'Brian, D.J., Bates, P.G., 1999. The use of moxidectin for the prevention and treatment of psoroptic mange (scab) in sheep. Veterinary Parasitology 83, 301–308. Perman, R., Ma, Y., McGilvray, J., Common, M., 2003. Chpt 8 Policy with imperfect information, Natural Resource and Environmental Economics, 3rd Ed. Pearson Education Limited, Harlow. Radostits, O.M., Blood, D.C., Gay, C.C., 1997. Veterinary medicine: a textbook of the diseases of cattle, sheep, pigs, goats and horses. Saunders, London. SEPA, 2006. Sheep dipping code of practice for Scottish farmers, crofters and contractors. http://www.sepa.org.uk/pdf/publications/ codes/sheep_dipping.pdf. Access date 28/11/06. SEPA, 2007. Groundwater: Legislation, Policy and Guidance. http:// www.sepa.org.uk/groundwater/lpg.htm. Access date 30/5/07. Spence, T., 1951. Control of sheep scab in Britain. The Australian Veterinary Journal 136–146. Steenland, K., 1996. Chronic neurological effects of organophosphate pesticides. BMJ 312, 1312–1313. Swanston, D., Shaw, I., 1990. Organophosphorus. The sheep farmer October 1990, pp. 31–33. Taylor, M.A., 2001. Recent developments in ectoparasiticides. The Veterinary Journal 161, 253–268.

33

Taylor, S.M., 1999. Sheep scab-environmental considerations of treatment with doramectin. Veterinary Parasitology 83, 309–317. Tellam, R.L., Bowles, V.M., 1997. Control of blowfly strike in sheep: current strategies and future prospects. International Journal for Parasitology 27, 261–273. Urquhart, G.M., Armour, J., Duncan, J.L., Dunn, A.M., Junnings, F.W., 1996. Veterinary Parasitology. Blackwell Science, London. van den Broek, A.H., Huntley, J.F., 2003. Sheep scab: the disease, pathogenesis and control. Journal of Comparative Pathology 128, 79–91. VMD, 1999. Veterinary medicinal products (dips, injectables, pour ons and sprays) available in the UK for use as ectoparasiticides in sheep. Veterinary Medicines Directorate, Addlestone. VMD, 2000. Compendium of data sheets for Veterinary Products 1999–2000. National Office of Animal Health, Middlesex. VMD, 2001. The Veterinary Medicines Directorate annual report and accounts 2000/01. VMD, Norwich. VMD, 2005. Veterinary medicinal products (dips, injectables, pour ons and sprays authorised in the UK for use against ectoparasites in sheep. Veterinary Medicines Directorate, Addlestone. VMD, 2006. Marketing Authorisations for Cypermethrin Sheep Dips are Suspended. http://www.vmd.gov.uk/General/Sheepdip/ 148836.htm. Access date 23/2/06. Wall, R., French, N.P., Morgan, K.L., 1995. Population suppression for control of the blowfly Lucilia sericata and sheep blowfly strike. Ecological Entomology 20, 91–97.