Get access to all handy features included in the IVIS website
- Get unlimited access to books, proceedings and journals.
- Get access to a global catalogue of meetings, on-site and online courses, webinars and educational videos.
- Bookmark your favorite articles in My Library for future reading.
- Save future meetings and courses in My Calendar and My e-Learning.
- Ask authors questions and read what others have to say.
Does local anaesthetic reduce pain in rubber ring castration of neonatal lambs?
Higgins, H.
Get access to all handy features included in the IVIS website
- Get unlimited access to books, proceedings and journals.
- Get access to a global catalogue of meetings, on-site and online courses, webinars and educational videos.
- Bookmark your favorite articles in My Library for future reading.
- Save future meetings and courses in My Calendar and My e-Learning.
- Ask authors questions and read what others have to say.
Read
PICO question
In lambs less than 7 days old undergoing castration with rubber rings does administration of local anaesthetic compared to no local anaesthetic result in a reduction of pain-related behaviours?
Appraisal, application and reflection
In the UK there is currently no legal requirement for local anaesthestic (LA) to be used when castrating lambs less than one week old with rubber rings.
The papers reviewed here covered a 30 year period of research into pain reduction for castration in lambs. Markers of pain used for outcomes were mostly plasma cortisol (Mellor & Murray, 1989) and behavioural expressions and postures which have been demonstrated to be sensitive markers of pain associated with castration in lambs (Mellor & Murray, 1989; Molony et al., 1993; and Molony et al., 2002). A method of assessing acute pain in lambs has been validated by Molony et al. (2002) and these observations formed the basis for behavioural measurements in many of the papers reviewed. Power calculations for sample size were not included in any of the papers and confidence intervals were rarely reported in the results.
Wood et al. (1991) concluded that lignocaine injected into the spermatic cords, scrotal neck and testes concurrently 15–20 minutes before castration resulted in the demonstration of fewer pain related behaviours and also diminished the increases in plasma cortisol in the immediate post-treatment period compared to those castrated without LA. The lambs receiving LA showed behavioural and cortisol responses close to those of the control group. This was, however, a study of small sample size that was not randomised or blinded, giving potential for bias in the results, therefore the power of the study is also unknown.
Thornton & Waterman-Pearson (1999) used the same LA protocol as Wood et al. (1991) in their study and also found that LA reduced plasma cortisol to similar levels to the control, and significantly reduced pain behaviours demonstated by lambs when compared with castration without LA. This study was the only one to assess scrotal pain as an outcome and found than LA significantly reduced the scrotal pain associated with rubber ring castration. This was a complex factorial study and although the sample size was larger than most of the other studies, only six lambs received each combination of treatments and outcome measures.
Whilst these studies (Thornton & Waterman-Pearson, 1999; and Wood et al., 1991) suggest that LA does significantly reduce the pain associated with rubber ring castration, in both cases the LA was administered 15 minutes before rubber ring application. On commercial sheep farms it may not be practical or efficient to handle each lamb twice and allow 15 minutes to elapse between injection of LA and application of the rubber ring. The other studies reviewed here investigate the effect of LA injected immediately before or after rubber ring application.
Studies conducted in Australia and New Zealand have demonstrated that lambs receiving LA immediately before or after rubber ring application showed fewer behaviours associated with pain in the first hour after castration (Jongmanet al., 2016; Small et al., 2020; and Stewart et al., 2014). However, as it is common in these countries to castrate lambs at ‘marking’ (marking being the gathering of lambs for the procedures of tail docking, castration of males, ear marking, ear tagging, vaccination, and drenching, often performed at between 6 and 12 weeks of age), rather than in the neonatal period, all of these studies used a population of lambs over four weeks old. The testes would be more developed, with a larger scrotal neck, than lambs less than seven days old being castrated in the UK, consequently the findings may not be directly applicable to the UK population.
In lambs less than 8 days old painful behaviours and plasma cortisol are significantly reduced if LA is administered at the time of rubber ring placement (Kent et al., 1998; Kent et al., 2004; Mellema et al., 2006; and Molony et al., 2012). LA was injected subcutaneously into the neck of the scrotum (in at least two sites in order to create a rubber ring block), the middle of the testes, into the spermatic cords or a combination of some or all of these sites, at the time of rubber ring application. All protocols gave similar results i.e. a significant reduction in pain related behaviours but not complete elimination. One study (Mellema et al., 2006) found that the subjective assessment of immediate pain was not significantly reduced, but other behavioural measurements based on the validated method were. In addition, the plasma cortisol did not significantly change compared to the control. These studies are mostly randomised controlled trials and provide strong evidence that pain is relieved by the use of LA at the time of rubber ring application, excluding the Kent et al. (1998) study which was not randomised.
Injecting LA at the time of castration is more time-efficient than injecting it 15 minutes before but there is still a time cost; rubber ring castration takes an average of 29 seconds and injection into the scrotal neck followed immediately by rubber ring castration takes an average of 68 seconds (Kent et al., 2004). Efforts have been made to further streamline the process by combining the LA injection and rubber ring application into one action using a preparatory device, Numnuts®, which delivers 1.5 ml lignocaine 2% into the dorsal midline of the scrotal neck immediately after the rubber ring is applied. Two studies investigating the effect of this precise method of LA injection were identified during the literature search (Jongman et al., 2016; and Small et al., 2020) but were excluded as both studies were conducted in Australia and the lambs were over four weeks old. These studies do suggest that LA administered in this way has a limited impact on pain but there is currently no evidence regarding its use in lambs less than seven days old.
With the exception of one paper that used procaine 5% (Molony et al., 2012) all LA intervention used lignocaine 2%, however, lignocaine 2% is not available for use in food producing animals in the UK. While no local anaesthetics are licensed for sheep in the UK, procaine may be prescribed under the cascade. Small et al. (2021) suggests that procaine may have a similar onset time to lignocaine but that the effect may last longer in lambs castrated by rubber rings.
In conclusion, LA administered into the scrotal neck, spermatic cord and testes of lambs 15 minutes before castration with rubber rings may virtually eliminate pain. However, where this is not possible, injection of 0.3 ml of lignocaine 2% into the scrotal neck or each testis of a neonatal lamb at the time of castration may aid reduction of pain.
Get access to all handy features included in the IVIS website
- Get unlimited access to books, proceedings and journals.
- Get access to a global catalogue of meetings, on-site and online courses, webinars and educational videos.
- Bookmark your favorite articles in My Library for future reading.
- Save future meetings and courses in My Calendar and My e-Learning.
- Ask authors questions and read what others have to say.
About
Affiliation of the authors at the time of publication
Harper Adams University, Newport, Shropshire TF10 8NB
Corresponding author email: [email protected]
Copyright Statement
© All text and images in this publication are copyright protected and cannot be reproduced or copied in any way.Related Content
Readers also viewed these publications
Subscribe
Veterinary Evidence is an online, open access, peer-reviewed journal owned and published by RCVS Knowledge. If you would like to receive updates on recent publications, you can register here. If you would like to submit an manuscript for publication in the Veterinary Evidence journal, you can consult the Guidelines for Authors.
Comments (0)
Ask the author
0 comments