Tail docking and castrating lambs: does the administration of local anaesthetic or meloxicam reduce the pain response exhibited?

a Knowledge Summary by

Evangeline Dunthorne BVMSci (Hons)MRCVS ^1*

¹The University of Surrey School of Veterinary Medicine, Daphne Jackson Road, Guildford, GU2 7AL
^*Corresponding Author (edunthorne13@gmail.com)

Clinical scenario

You are a veterinarian who has been called for advice from a sheep farmer. The farmer is planning on performing all their castrates and tail docking themselves using rubber rings. They noticed last year many sheep exhibited behavioural and physical signs of pain after the procedures. They have asked whether they should use meloxicam or local anaesthesia to reduce this occurrence. Due to lack of licensing in the UK for either of these drugs for this purpose you are unsure which one to recommend (BVA, 2020).

The evidence

Four studies were found to be relevant to the PICO question, three of these were randomised and blinded (Kells et al., 2019; Smalls et al., 2014; and Smalls et al., 2020) reducing levels of selection and observer bias. The variables measured included; time spent performing different behaviours (Kells et al., 2019; Small et al., 2014; Kent et al., 1998) and time taken to ‘mother-up’, meaning time taken for lamb and mother to relocate each other after separation(Small et al., 2014; and Small et al., 2020). Within the behaviour category, acute pain related behaviour was observed alongside postures such as lying and standing. Included in the outcomes measured were parameters less relevant to the PICO such as cortisol levels (Kent et al., 1998) and wound development (Small et al., 2014) and therefore these were disregarded.

There was one study that contained both meloxicam and lidocaine and therefore fulfilled the inclusion criteria in its entirety; Kells et al. (2019). Additional to a control, groups were given either lidocaine subcutaneously (SC) or meloxicam intramuscularly (IM) or alternatively, given them both in combination. The group given both forms of analgesia was not important to this summary as it does not compare their efficacy. Meloxicam was given intramuscularly in the aforementioned study and buccally in the Small et al. (2014) study, whilst Kent et al. (1998) and Small et al. (2020) looked at the effect of lidocaine. All studies differed in route of administration of said anaesthesia and as such are difficult to directly compare.

It can be concluded from these studies that both types reduce pain responses post-marking but at different times, with meloxicam unsurprisingly providing more longer-term pain relief and lidocaine benefiting acutely. More evidence is required to directly compare the methods of anaesthesia/analgesia and decide which would be more efficacious in a clinical scenario.

Summary of the evidence

Appraisal, application and reflection

According to The Mutilations Regulations 2007 (The Mutilations Act, 2007), if a lamb is aged 3 months or older at the time of tail docking or castration an anaesthetic must be used. Tail docking is routinely carried out to prevent faecal or urine contamination around the tail which can lead to flystrike and in worse case scenarios death. Castrations are carried out to reduce aggressive behaviours making animal handling easier and prevent unwanted pregnancies of ewes (BVA., 2020). This paper looks at the current anaesthesia and analgesia used in lambs during these procedures and compares their efficacy in the hope of encouraging its widespread implementation.

The strongest evidence for this PICO lies in Kells et al. (2019); it contains both meloxicam and lidocaine administration and compares their benefits. This study demonstrates a conventional method of lidocaine infusion subcutaneously (SC) into the scrotal neck, spermatic cord and tail, but the method of meloxicam administration intramuscularly (IM) precastration/docking is not highly reported. In a study based on meloxicam efficacy in sheep, it is advised that a dose of 1 mg/kg be given IM (Woodland et al., 2019), whereas, in Kells et al. (2019) the dose worked out at 20 mg/ml making it is more than double the required amount. Alongside this; length of time needed for both medications to take effect was not allowed as they were given just before the procedure. It has been demonstrated that 10–15 minutes should be permitted after LA administration for it to take effect (Wood et al., 1991). In addition, IM meloxicam reaches peak plasma concentration (Tmax) at 2–3 hours post administration (Woodland et al., 2019), therefore longer observation of pain behaviours would have been beneficial. In this study pain related behaviour including reduced time spent lying normally and increased time spent standing/walking abnormally was still seen after 5 hours observation. Kells et al. (2019) states no difference between the meloxicam group and the group that did not receive analgesia, but this may be due to the route of administration, time outcome was measured or onset of action. Moreover, no p-value was given for these results and so their significance is unknown. There is limited literature about onset of action time for meloxicam in sheep in the UK due to it being given on the cascade. Meloxicam was given buccally in Small et al. (2014) with its Tmax time stated as 2.6 hours for oral administration, despite this it was given immediately before the procedure similarly to Kells et al. (2019).

The route of administration also differed between studies for lidocaine. In the studies Kells et al. (2019) and Kent et al. (1998) it was given SC into the scrotal neck, spermatic cord and tail, in the latter, it was sometimes given via a high-pressure needleless injection. In Small et al. (2020) it was given by a piece of equipment called Numnuts® that injects at the time of castration, it can be argued that the aim of this study was more about the efficacy of the Numnuts® device rather than the benefits of lidocaine at marking. Numnuts® is for application in 4–8 week old lambs weighing 10–20 kgs and the active ingredient NumOcaine® is approved in Australia and New Zealand but not the UK. Additionally, lambs tend to be castrated before 4–8 weeks old in the UK and so their use in the UK is limited (Numnuts., n.d.). In Kent et al. (1998) it was not stated who received which method of lidocaine administration, for example who received high-pressure needleless injection or conventional SC injection and where this injection was given; either intratesticular or in the spermatic cord/neck of the scrotum. This makes the evidence weaker due to little control over the variables. The study later states that there was no significant difference between responses to route of administration, but this is hard to support with such a reduced sample size after subdividing them. Additionally, lidocaine was used with adrenalin increasing its duration of action and reducing its use in this PICO. Overall, the paper provides insufficient evidence as there were too many protocols being tested with little confirmation on groupings, method used or clearly stated aims.

Timing of measuring outcomes in all instances played a large part in what information was gathered. It could be said that for Kent et al. (2019) longer than 4 hours may have given more information on meloxicam and the delay of measurement at 15 minutes could have restricted what outcomes from lidocaine were seen. Lidocaine has a variable duration of action in sheep of about 90 minutes and a short onset of action of 2–5 minutes (Depenbrock, 2017) so any data collected between 0–30 minutes is imperative. Similarly, in Small et al. (2020) the behaviours were observed in 1 minute blocks rather than continuously allowing large windows for missing key signs. However, the best timetable for measurements was in both Small et al. (2014) and Small et al. (2020) which studied pain behaviours at 5, 20, 35, 50 minutes for lidocaine and for 8 hours and then again at 24 hours for meloxicam.

It may be difficult to compare the results between the studies due to the range of marking protocols used. Kells et al. (2019) used a rubber ring for castration and hot iron for docking, Small et al. (2014) used a knife for castration and hot iron for docking, Kent et al. (1998) and Small et al. (2020) used rubber rings for both procedures which was sometimes followed by a bloodless castrator (Kent et al., 1998). It has been shown that the method affects levels of stress and therefore can have an impact on behavioural responses (Molony et al., 1993), influencing the results in the trials. All except Kent et al. (1998) were randomised and blinded, reducing bias at selection and observation. Despite stating that the observer was blinded to treatment groups, in Kell et al. (2019) lambs in the SHAM group were distinguishable from the treated group, but this has little bearing on our review as a comparison is only needed between lambs that were castrated/docked with or without analgesia.

Most of the studies have an adequate sample size with the smallest being 60 lambs (Small et al., 2014). A smaller sample reduces the power of the study directly impacting the studies ability to demonstrate a statistical difference. Statistical significance depends on sample size and effect size, so even if the effect size is large if the sample size is small the results are not significant (Sullivan & Feinn, 2012), hence the data in Kent et al. (1998) being of reduced value once the groups had been designated. Three of the studies are based outside of the UK making their transferability more difficult. Kent et al. (1998) was based in Scotland but this paper is of least use. A difference created by location is the breeds examined, which may affect the stoic nature of the lambs. In the UK most lambs are ringed before 7 days old to conform to UK legislation, in Australia and New Zealand lambs are typically marked between 4–6weeks old. This is demonstrated in these studies whereby the populations of lambs outside the UK exceed 7 days. Many lambs in Australia and New Zealand are born outdoors and require gathering up for marking which is why it is difficult to perform the task in under 7 days (Numnuts, n.d.). This means that these studies have a greater resonance with UK farmers with hill sheep flocks.

Discouraging the non-randomised trial due to its weaknesses outlined above, the other three all show an improvement in aberrant behaviour. Lidocaine showed an acute effect after the procedure for example a significant reduction in pain behaviours at 5 (P<0.001) and 20 minutes (P = 0.001) were observed (Small et al., 2020). Meloxicam showed longer-term effects (Small et al., 2014), at 8 hours after marking there was a statistically significant reduction in combined abnormal behaviours (P<0.001) from 5.2% in the placebo group to 0.7% in the meloxicam group. Kent et al. (2019) demonstrated that in combination they proved more advantageous, showing a reduction in twisted lying, hindlimb stretching and tail lifting but the p-value was not stated and as such its significance cannot be determined. In Small et al. (2014) it was stated that 0.1>P>0.05 still indicates a tendency towards significance but typically P>0.05 supports evidence for the null hypothesis and so results including meloxicam increasing time spent grazing, lying and suckling can be disputed.

In conclusion, more evidence is required to compare the benefits of meloxicam to lidocaine when given before castration or tail docking. In the meantime, for lambs over the age of 3 months old anaesthesia must be used. Despite meloxicam having conflicting evidence, the use of LA or non-steroidal anti-inflammatories (NSAIDs) have their part to play in reducing pain post-procedure. Buccal meloxicam will cause delayed analgesia and SC lidocaine provides acute pain relief; they remain strong methods of pain control and current research is taking place for Numnuts® to be introduced in the UK. Using both an NSAID and local anaesthesia in combination requires more research to prove its efficacy and safety and is not covered by this PICO. As a result of the studies being taken from Australian and New Zealand flocks, the studies appraised in this paper will have more relevance to UK hill flocks and those castrating/docking late. Additionally, lidocaine does not have a maximum residue level (MRL), and both lidocaine and meloxicam are not licensed in the UK for this purpose. Subsequently, these papers are limited for practical application in the UK.

Methodology Section

Search Strategy
Databases searched and dates covered:	CAB Abstracts on OVID interface (1973– Oct 2020) PubMed on the NCBI website (1958 – Oct 2020)
Search strategy:	CAB Abstracts and PubMed: (lamb* or sheep) (castrat* or tail docking or marking) (meloxicam or local anaesthesia or analgesia or lidocaine or lignocaine) 1 AND 2 AND 3
Dates searches performed:	6 Oct 2020

Exclusion / Inclusion Criteria
Exclusion:	Paper not available in English Paper cannot be accessed Paper was a review or conference paper The study: Was not relevant to the PICO Did not contain meloxicam or local anaesthesia Use of a different NSAID Use of different local anaesthetic to lidocaine Did not look at pain response Lidocaine given topically rather than injected Looking at mulesing lambs instead of castration or tail docking The study was on sheep not lambs Incorrect species
Inclusion:	Any relevant primary research paper which compared the pain response with meloxicam or topical anaesthesia

Search Outcome
Database	Number of results	Excluded – Not relevant to the PICO	Excluded – Inaccessible	Excluded – Conference paper	Excluded – Review	Total relevant papers
CAB Abstracts	23	13	2	3	2	3
PubMed	44	33	3	0	4	4
Total relevant papers when duplicates removed						4

The author declares no conflicts of interest.

1. British Veterinary Association. (2020). Sheep castration, tail docking, and pain management. 1–7. Available at: https://www.bva.co.uk/media/3364/sheep-castration-tail-docking-and-pain-management-final.pdf [Accessed 1 November 2020]
2. Depenbrock, S. (2017). Ruminant Field Anaesthesia and Analgesia. Penn Conference. 1–5.
3. Kells, N.J., Beausoleil, N.J., Godfrey, A.J.R., Littlewood, K.E., Ward, R.N. & Johnson, C.B. (2019). Effect of analgesic strategies on pain behaviour associated with combined ring castration and hot iron tail docking in Merino lambs. Applied Animal Behaviour Science. 222. DOI: http://dx.doi.org/10.1016/j.applanim.2019.104914
4. Kent, J.E., Molony, V. & Graham, M.J. (1998). Comparison of methods for the reduction of acute pain produced by rubber ring castration or tail docking of week-old lambs. The Veterinary Journal. 155(1), 39–51. DOI: https://doi.org/10.1016/S1090-0233(98)80033-6
5. Molony, V., Kent, J.E. & Robertson, I.S. (1993). Behavioural responses of lambs of three ages in the first three hours after three methods castration and tail docking. Research in Veterinary Science. 55(2), 236–245. DOI: http://dx.doi.org/10.1016/0034-5288(93)90087-V
6. (n. d.). Numnuts® availability in the UK. Available at: https://numnuts.store/is-numnuts-available-in-the-uk/ [Accessed 27 December 2020]
7. Small, A., Belson, S., Holm, M. & Colditz, I.G. (2014). Efficacy of a buccal meloxicam formulation for pain relief in Merino lambs undergoing knife castration and tail docking in a randomized field trial. Australian Veterinary Journal. 92(10), 318–388. DOI: http://dx.doi.org/10.1111/avj.12241
8. Small, A.H., Jongman, E.C., Niemeyer, D., Lee, C. & Colditz, I.G. (2020). Efficacy of precisely injected single local bolus of lignocaine for alleviation of behavioural responses to pain during tail docking and castration of lambs with rubber rings. Research in Veterinary Science. 133, 210–218. DOI: http://dx.doi.org/10.1016/j.rvsc.2020.09.025
9. Sullivan, G.M. & Feinn, R. (2012). Using Effect Size – or Why the P Value Is Not Enough. Journal of Graduate Medical Education. 4(3), 279–282. DOI: https://dx.doi.org/10.4300%2FJGME-D-12-00156.1
10. (2007). The Mutilations (Permitted Procedures) (England) Regulations 2007. Available at: https://www.legislation.gov.uk/ukdsi/2007/9780110757797/contents/data.html [Accessed 1 November 2020]
11. Wood, G.N., MoLony, V., Fleetwood-Walker, S.M., Hodgson, J.C. & Mellor, D.J. (1991). Effects of local anaesthesia and intravenous naloxone on the changes in behaviour and plasma concentrations of cortisol produced by castration and tail docking with tight rubber rings in young lambs. Research in Veterinary Science. 51(2), 193–199. DOI: http://dx.doi.org/10.1016/0034-5288(91)90013-E
12. Woodland, A.N., Van der Saag, D., Kimble, B., White, P.J., Govendir, M. & Lomax, S. (2019). Plasma pharmacokinetic profile and efficacy of meloxicam administered subcutaneously and intramuscularly to sheep. PLOS ONE. DOI: http://dx.doi.org/10.1371/journal.pone.0215842