RESUMEN SUPERVISIÓN EFECTIVA

Although, the mechanisms of pain in animals and humans are similar, pain in animals is difficult to understand and detect accurately. There have been many arguments about animal pain over past years.

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Animals lack speech and therefore for years, the dispute on “can animals feel pain” was on- going (Musk, 2013, Paul-Murphy et al., 2004). However, now it is almost universally accepted that animals do feel pain but the expression of pain varies in different species (Rutherford, 2002). The IASP (1979) suggested that the inability to communicate does not mean that the individual is not experiencing pain.

Pain detection and amelioration are therefore important components in animal care and welfare (Anil et al., 2005, Barnett, 1997). It is reported that animal and human pain are similar in terms of physiological, pathological and emotional components (Panksepp, 2005, Yaksh et al., 1999, Bennett and Xie, 1988, Berkowitz, 1983). Many of the pain management strategies for humans are based on animal models (Morton and Griffiths, 1985). This has been possible due to the similar neuronal pathways and neurotransmitter receptors in animals and humans (Livingston, 2010).

It has been suggested that new-born and young animals may experience pain more intensely than do older animals (Moss et al., 2007, Johnson et al., 2005, Mellor and Gregory, 2003). On the contrary it has been argued that the infants under the age of one year do not feel pain (Derbyshire, 2003).

According to the Animal Welfare Act (1999), a painful procedure is defined as any procedure that reasonably would be expected to cause more than slight and momentary pain or distress in a human being (AWIC, 2000).It has been argued that animals should receive the benefit of the doubt (Anil et al., 2005).

Many husbandry procedures in animals such as castration, tail docking, disbudding or destruction of the horn bud, dehorning, branding, debeaking and even management practices such as shackling, transport, milking, housing etc. may result in acute pain, (Sneddon and Gentle, 2000) compromising animal welfare (Grant, 2004).

In addition to the routine surgical and other practices, farmed animals tend to acquire injuries from fighting and various activities. The systemic conditions such as pneumonia, enteritis, arthritis, mastitis, foot rot etc. are also painful leading to acute or chronic pain (Molony and Kent, 1997). Acute pain is usually a short term pain associated with the development of protective mechanisms to prevent further processing of pain (Greisen et al., 1999). However,

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on-going acute pain which ultimately results in chronic pain is not beneficial. Chronic pain in farmed animals leads to poor appetite, poor growth and production (Molony et al., 1995, Dantzer and Mormède, 1983). Therefore, the welfare as well as production of the animals is compromised and in such conditions, analgesic treatment and proper animal care is warranted (Stafford and Mellor, 2005, Anil et al., 2005). The qualitative and/or quantitative assessment of pain in animals is essential for the management of painful conditions and welfare improvement (Fitzpatrick et al., 2006).

1.2.2.1 Pain in sheep

Sheep are susceptible to various diseases and either infectious or non-infectious diseases can compromise welfare of sheep by generating pain (Fitzpatrick et al., 2006).

1.2.2.1.1 Lameness

Sheep lameness is caused due to pain and this pain is associated with many conditions such as foot and mouth disease to footrot (Winter, 2008). However, 80 per cent of lameness in sheep is caused by footrot and interdigital dermatitis in UK (Kaler and Green, 2009). Also in many other countries of the world, lameness due to footrot is reported and lameness in sheep is global problem (FAW, 2011). Therefore, assessment of lameness and its treatment/management is a requirement for improving sheep welfare.

1.2.2.1.2 Footrot

Footrot is an acute, sub-acute or chronic disease of sheep which mainly affects sheep feet (Murnane, 1933). The causative agent of this disease is Dichelobacter nodosus,(D.nodosus) which is active after initial infection of the feet with Fusobacterium necroforum (F. necroforum) bacteria which causes interdigital infection followed by footrot lesions (Winter, 2008).

Pre-disposing factors for footrot are wet conditions (mud during winter, faeces), humidity (temperatures above 10°C) which deteriorate interdigital skin and provide favourable conditions to F. necroforum to proceed with further damage which allows entry of D. nodosus (Morck et al., 1994). The damp conditions are also responsible for the transmission of the disease between sheep (Green and George, 2008). Potentially the bacteria produce

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protease enzyme which acts on the hoof tissue and causes under-running hoof leading to virulent footrot (Winter, 2008). Another mild or benign footrot type is also developed by the similar causative agent but there is no damage to hoof as the strain of F. nodosus is not virulent and only inflammation of interdigital skin is observed (Egerton et al., 1969).

Samples from footrot lesions confirm the presence of both D. nodosus and F. necroforum

with several strains where D. nodosus with type IV fimbriae are responsible for virulence due to production of serine proteases (Kennan et al., 2011). General clinical signs observed in sheep during footrot are severe lameness, poor feed intake, isolation from the herd, loss of body condition and ultimately lowered growth and production (wool, meat) etc. causing impact on the welfare and economics (Bennett and Hickford, 2011).

Typical footrot treatment consists of parenteral antibiotics, foot baths of either formalin (2- 3%) or zinc sulphate (10-20%) solution, hoof trimming in very severely affected feet, isolation of the affected animals and provision of clean and dry environment to prevent the transmission of the disease within the herd (Winter, 2008). Also, vaccination for prevention of footrot is available. However, the presence of multiple strains of causative bacteria restricts the utility of these vaccines (Schwartzkoff et al., 1993).

Pain due to footrot can be managed with other treatment strategies such as use of analgesic (NSAIDs) drugs as they have demonstrated efficacy to minimise pain due to lameness (Welsh and Nolan, 1995).