Clasificación de indisciplina

Trimming or paring of hoof horn is frequently used as both a control and treatment measure to reduce the prevalence of FR and lameness in UK sheep flocks (Morgan, 1987). Until 2002 foot trimming was recommended as both a control and treatment measure for FR in UK flocks (Morgan, 1987; Winter, 1998). Unsurprisingly therefore, results from two stratified random UK postal surveys reported that routine foot trimming was used as a control measure by 87% and 76% of farmers in 1994 and 2004 (Grogono-Thomas and Johnston, 1997; Kaler and Green, 2009). Similarly, therapeutic foot trimming was reported to be the most frequently used treatment for FR, carried out by >90% of farmers in the UK in 2000 and 2004 (Wassink et al., 2003a; Kaler, 2008). However, despite widespread and popular use, there are no randomised controlled trials evaluating the role of foot trimming as a control measure and none as a treatment measure until 2010 (Kaler et al., 2010a). In addition, there have been a number of studies published that raise considerable doubts about their efficacy and there has been some debate in the UK whether or not they should be used.

In 1983 Skerman et al. raised doubts about the use of therapeutic foot trimming prior to foot bathing. In a series of controlled experiments the authors demonstrated that foot trimming prior to foot bathing, in either formalin or zinc sulphate solutions, did not significantly benefit the therapeutic effect of foot

bathing. In 1994, a UK stratified random postal survey published by Grogono- Thomas and Johnston (1997) reported a positive association between high levels of FR and routine foot trimming. This finding was reproduced by Wassink et al. (2003a) who reported an association between higher prevalence of FR and ID (Wassink et al., 2004) on farms where routine foot trimming was practiced more than once a year; in a retrospective study of 251 farmers that compared management and prevalence of FR and ID in 2000. The study also reported a positive association between the prevalence of FR and therapeutic foot trimming (Wassink et al., 2003a). These authors raised questions on the use of routine foot trimming as an effective control measure. They hypothesised that the trimming of healthy and diseased hooves increased transmission via two potential routes: Firstly, through environmental contamination, i.e. as a result of the higher stocking density during gathering and penning. Secondly through increased susceptibility of sheep to disease either via excessive trimming, where the sensitive tissues of the foot are exposed or, where knives or foot shears are not disinfected between sheep and feet, direct inoculation of D. nodosus. They recommended that further studies be conducted. Their findings were however criticised by Abbott et al. (2003) because the study design was observational and retrospective, and Abbott et al. (2003) stated that the authors could not infer a causal relationship (although Wassink et al. (2003a) had in fact raised hypotheses). Abbott et al. (2003) proposed an alternative explanation that high levels of FR in a flock could lead to farmers trimming more regularly. Wassink et al. (2003b) responded with a follow up study with 80 of the farmers from their

Chapter 2 Page 24 earlier was strengthened by the fact that the majority of the farmers followed up (77%) had not changed their practices for more than 5 years.

In 2002 a longitudinal study was carried out on one farm by Green et al. (2007a). Results from this study reinforced the negative association previously reported between routine foot trimming and an increased incidence of ID and FR by earlier studies. Although, converse to Wassink et al. (2003a; 2004) a negative association between therapeutic foot trimming and the incidence of ID and FR was also reported. A second hypothesis was generated by these authors: that foot trimming (whether routine or therapeutic) was detrimental to foot health.

Further weight to this hypothesis was added by Kaler and Green (2009) from a stratified random postal survey with 809 English sheep farmer respondents carried out in 2004. The results again suggested that routine foot trimming was significantly associated with a higher prevalence of ID, FR and lameness. Furthermore that routine foot trimming just once a year was associated with an increased risk. This was slightly more extreme than the associated risk reported by Wassink et al. (2003a; 2004) as only being significant when routine foot trimming was carried out twice or more per annum. Wassink et al. (2003a; 2004) did not report or analyse the number and percent of farms that routinely foot trimmed ‘once’ or ‘never’ separately in their publication; neither did they report why these categories were combined. It may have been that there were too few farms in the ‘once’ or ‘never’ category for data to be analysed separately, and the data combined produced misleading results. Wassink et al. (2003a; 2004) had 251 respondents, their target population selected from a compliant group of farmers who had expressed interested in taking part in further research after the 1994

survey by Grogono-Thomas and Johnston, and therefore were not randomly selected. In comparison Kaler and Green (2009) had 809 respondents from a random sample of sheep farmers stratified by region and flock size within region, obtained from EBLEX (the organisation for the English beef and sheep meat industry). It is therefore proposed that more weight should be given to the findings of Kaler and Green (2009).

In 2007 a randomised factorial-design clinical trial was conducted by Kaler et al. (2010a) on one farm in England to examine time to recovery using 6 treatments, that included therapeutic foot trimming used alone and in combination with other antibacterials. Results showed that therapeutic foot trimming delayed recovery regardless of whether or not it was combined with topical or parenteral antibiotics. The authors concluded that therapeutic foot trimming, even when it did not cause bleeding, was in fact detrimental and should not be recommended. The study did not however involve any non-lame sheep and the effect of routine foot trimming in a randomised clinical trial has still not been investigated. Kaler et al. (2010a) did, however, propose a third hypothesis: that routine foot trimming might have an indirectly causal relationship where farmers use routine foot trimming as a control measure but then neglect to treat individual lame sheep i.e. choosing to use whole flock control measures rather than treat lame individuals (Kaler and Green, 2009; Kaler et al., 2010a). This hypothesis is entirely plausible given that farmers who do not treat individual lame sheep (and therefore use whole flock control measures) have a higher prevalence of lameness (Kaler and Green, 2009) and that routine foot trimming is also associated with a higher prevalence of lameness (Grogono-Thomas and Johnston, 1997; Wassink et al., 2003a; 2003b; 2004; Green et al., 2007a; Kaler and Green, 2009).

Chapter 2 Page 26 By 2009 advice given to farmers by veterinary practitioners was still somewhat varied, a few still recommended rigorous trimming of the horn at diagnosis (Duncanson, 2009). An increasing majority (>50%) recommended hoof horn should be trimmed carefully only after lesions were healing and 5 days after treatment (Winter, 2004b; EBLEX, 2008a). However these recommendations were not based on any scientific evidence. Furthermore, in 2010 Wassink et al. (2010b) reported results of a farmer satisfaction poll with regard to current and ideal management practices. Up to five current management practices used to prevent FR were listed by 161 farmers in 2006. Therapeutic foot trimming of lame sheep was listed as the most popular management practice (66% of farmers) and routine foot trimming listed as the least popular (39% of farmers) of farmers top five management practices. Of those that routinely foot trimmed, 22% trimmed all the feet of all their ewes and 16% trimmed more than half of their ewes’ feet. While it was not drawn attention to by the authors, of concern is that 99 (62%) of the farmers in this survey carried out therapeutic foot trimming to treat ID. The aetiology of ID and FR is linked (see Chapter 1). Foot trimming sheep with ID is likely to lead to increased recovery time, particularly if the sensitive tissues of the foot are exposed; as well as increasing transmission of D. nodosus via direct inoculation from shears/knives. The study highlighted that foot trimming the feet of all ewes more than once a year was associated with famers feeling unsatisfied with their use of time and that whole flock control measures (such as routine foot trimming) were associated with higher prevalence of lameness (>5 cf. ≤5%). These authors proposed that if foot trimming was demonstrated to be detrimental or ineffective these results would be easily accepted by farmers and that further research was needed.

Foot trimming is a skilled procedure, which requires a sharp paring tool (usually a knife or foot shears) and ‘adequate restraint’ for the sheep (Morgan, 1987). Care and attention is required in order to avoid damage to hooves that can result in lameness (Hosie, 2004) or, hypothetically, give causative agents a site to colonise the hoof (Wassink et al., 2003a; 2004). Sheep at pasture have a hoof horn growth rate of 3.6mm per month (Shelton et al., 2012), perhaps less in colder months (Wheeler et al., 1972) and hoof horn growth may vary by age (Dekker et al., 2005), diet (Butler and Hintz, 1977; Buffa et al., 1992; Smith et al., 1999), environment (Vokey et al., 2001) and breed (Shelton et al., 2012). Consequently, if a farmer trims a hoof to expose just 5mm of sensitive tissue it could take >6 weeks to re-grow leaving the foot susceptible to infection for this period. Conversely if a foot is trimmed once per year it will have grown ~ 43mm by the next foot trim, and so sheep hoof horn would either be very overgrown or have worn away. It is also well documented that foot trimming that results in bleeding or damage to the sensitive tissues of the foot causes pain and can lead to the formation of toe granulomas (Morgan, 1987; Hosie, 2004; Winter, 2004a; 2004b), persistent lameness (Morgan, 1987; Winter, 2004a) and these sheep may be more likely to develop footrot (Kaler et al., 2010b), either because of increased susceptibility to a new infection or recrudescence of existing infection.

There is very little literature on the standard to which foot trimming is carried out by sheep farmers. Grogono-Thomas and Johnston (1997) visited 30 farmers in a follow up to their 1994 postal survey. They reported that 50% of the farmers visited did not have a good technique; 10% of these were considered to have extremely bad technique that could in fact attribute to increased levels of lameness on these farms. Furthermore, none of the farmers visited disinfected trimming

Chapter 2 Page 28 apparatus between infected and healthy feet; although, Abbott et al. (2003) suggests that this practice is unimportant where sheep have been co-grazing beforehand. Wassink et al., (2005) reported that 50% of farmers trimmed to either reshape the foot or to remove overgrowth. To the author’s knowledge, there is no further research on foot trimming technique. Given that at least 66% of farms have sheep with toe granulomas (Kaler and Green, 2008a) and that one reason toe granulomas develop is as a result of damage to the sensitive tissue of the dermis through excessive trimming it is probable that poor foot trimming technique is quite widespread.

Finally, farmers indicated that it takes on average 1 hour to foot trim 15 sheep (Wassink et al., 2005). Consequently, if foot trimming was proved to be either detrimental or not beneficial to the control of lameness, a farmer’s time would be better spent on implementing an alternative treatment and control programme(s) that has proved to be cost and time effective.

2.1.1

Study aims

The aims of this study were to use a within farm stratified random control clinical trial to examine the effect of routine foot trimming compared with no routine foot trimming on lameness in sheep.

2.1.2

Study hypotheses

Four alternative hypotheses concerning routine foot trimming were tested:

1. Routine foot trimming is detrimental.

3. Routine foot trimming instead of treatment results in a high prevalence of lameness.

4. The technique of routine foot trimming is important.