Effects of acute pain reduction methods on the chronic inflammatory lesions and behaviour of lambs castrated and tail docked with rubber rings at less than two days of age

The Neuroimmune Interface and Chronic Pain Through the Lens of Production Animals

Communication between the central nervous system (CNS) and the immune system has gained much attention for its fundamental role in the development of chronic and pathological pain in humans and rodent models. Following peripheral nerve injury, neuroimmune signaling within the CNS plays an important role in the pathophysiological changes in pain sensitivity that lead to chronic pain. In production animals, routine husbandry procedures such as tail docking and castration, often involve some degree of inflammation and peripheral nerve injury and consequently may lead to chronic pain. Our understanding of chronic pain in animals is limited by the difficulty in measuring this pathological pain state. In light of this, we have reviewed the current understanding of chronic pain in production animals. We discuss our ability to measure pain and the implications this has on animal welfare and production outcomes. Further research into the neuroimmune interface in production animals will improve our fundamental understanding of chronic pain and better inform human clinical pain management and animal husbandry practices and interventions.

Can Lambs in Pain Identify Medicated Feed?

Lambs in Australia undergo painful husbandry procedures as part of common husbandry. The magnitude and duration of pain are difficult to assess in lambs. Most currently used methods rely on behavioral expressions and physiological markers that may fail to detect the state of pain an animal experience. This study examined motivation of 12-week-old lambs experiencing chronic pain to self-medicate by consumption of feed containing an analgesic agent as an indicator of pain in lambs. In this study, 36 male Merino lambs were individually penned and acclimated to pelleted feed and two artificial odors: strawberry and banana. Once acclimated to odored feed, lambs were tested for their individual preference for the odors. Lambs were then assigned to one of two groups: Sham—sham handled day 0 and 7 or Ring—Ring castrated day 0 and tail docked day 7. To enable self-medication testing, lambs underwent a conditioning period (day 0–3) followed by the self-medication period (day 7–12). On day 0 lambs were castrated or sham handled, and then offered only medicated feed that contained an odor cue (either strawberry or banana). On day 7, lambs underwent tail-docking or sham handling and were offered both the conditioned medicated feed and non-medicated feed. Amount of each feed consumed was recorded 1 and 12 h after offer each day. Blood samples were taken for cortisol and white blood cell analysis and behavioral observations were recorded for 12 h following treatment. There was no difference in preference for medicated feed between Ring and Sham lambs during the self-medication phase (P = 0.18). Lambs in both groups displayed a significant preference for strawberry cued medicated feed during the self-medicated period when compared to the other testing periods (P = 0.05). Ring lambs displayed more active pain behaviors (mean = 15.1) than Sham (mean = 0.4, P < 0.05). Following castration, Ring lambs had a higher neutrophil/lymphocyte ratio at 6, 24, 48, and 72 h. This study was not able to demonstrate that lambs can self-medicate for a state of pain.

Local Anesthetic Delivered with a Dual Action Ring and Injection Applicator Reduces the Acute Pain Response of Lambs during Tail Docking

Simple Summary

Tail docking is a procedure practiced on millions of lambs all over the world. The objective is to prevent fecal soiling on the lower part of the tail, reduce soiling of the breech, and thereby lessen the risk of blowfly strike. Docking can be done with a knife or a clamp, but applying a latex ring round the tail, cutting off the blood supply so that the tail drops off a few weeks later, is the most popular method. All methods cause acute pain which diminishes substantially after the first hour. The present trial determined whether local anesthetic delivered by a prototype Numnuts^® device, a novel, dual-function applicator, would reduce this pain in two to four-week-old lambs. Comparison of lambs that were sham handled, lambs that underwent ring tail docking and a third group of lambs that underwent ring tail docking and that were injected with lignocaine using the dual function device was conducted. All lambs were returned to their pen with their mothers and videoed for three hours for behavioral signs of pain. Every five minutes for the first hour and then every ten minutes, each lamb’s posture, movement and feeding behavior was classified and quantified, and the data subjected to statistical analysis. It was concluded that applying lignocaine using the novel device greatly reduced the degree of pain observed.

Abstract

Docking the tail of lambs is a standard husbandry procedure and is achieved through several techniques including clamps, hot or cold knives and latex rings, the last of which is the most popular. All tail docking methods cause acute pain which can be reduced by application of local anesthetic, however precise anatomical injection for optimal efficacy requires considerable skill. This pen trial evaluated the ability of local anesthetic (LA) delivered with a dual function ring applicator/injector to alleviate acute tail docking pain. Thirty ewe lambs were assigned to one of three treatment groups (n = 10 per group): ring plus local anesthetic (Ring LA), ring only (Ring) and sham handled control (Sham). Lambs were videoed and their behavior categorized every five minutes for the first hour and every 10 min for the subsequent two hours after treatment. There was a significant effect (p < 0.001) of treatment on total active pain related behaviors in the first hour, with Ring lambs showing higher counts compared to Ring LA or Sham. Ring lambs also displayed a significantly higher count of combined abnormal postures (p < 0.001) than Ring LA or Sham lambs. Delivery of 1.5 mL of 2% lignocaine via the dual action device abolished abnormal behaviors and signs of pain in Ring LA lambs. However, lambs in the Ring LA group spent less time attempting to suckle compared to Ring and Sham lambs, suggesting that some residual discomfort remained.

Analgesia for Sheep in Commercial Production: Where to Next?

Simple Summary

Increasing societal and customer pressure to provide animals with ‘a life worth living’ continues to apply pressure on industry to alleviate pain associated with husbandry practices, injury and illness. Although a number of analgesic solutions are now available for sheep, providing some amelioration of the acute pain responses, this review has highlighted a number of potential areas for further research.

Abstract

Increasing societal and customer pressure to provide animals with ‘a life worth living’ continues to apply pressure on livestock production industries to alleviate pain associated with husbandry practices, injury and illness. Over the past 15–20 years, there has been considerable research effort to understand and develop mitigation strategies for painful husbandry procedures in sheep, leading to the successful launch of analgesic approaches specific to sheep in a number of countries. However, even with multi-modal approaches to analgesia, using both local anaesthetic and non-steroidal anti-inflammatory drugs (NSAID), pain is not obliterated, and the challenge of pain mitigation and phasing out of painful husbandry practices remains. It is timely to review and reflect on progress to date in order to strategically focus on the most important challenges, and the avenues which offer the greatest potential to be incorporated into industry practice in a process of continuous improvement. A structured, systematic literature search was carried out, incorporating peer-reviewed scientific literature in the period 2000–2019. An enormous volume of research is underway, testament to the fact that we have not solved the pain and analgesia challenge for any species, including our own. This review has highlighted a number of potential areas for further research.

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

Delivery of local anaesthetic at the time of castration and tail docking (marking) could improve welfare outcomes in lambs. This study examined pain responses in lambs marked using rubber rings, with or without local anaesthetic precision injected using the Numnuts® instrument. On each of two commercial farms, 150 prime lambs aged 4 to 10 weeks, balanced for sex, were randomly allocated to 3 treatments: handled in a lambing cradle (Sham), handled and marked with rubber rings (Ring) or handled and marked with rubber rings and treated with 30 mg lignocaine using the Numnuts® instrument (NNLA). Time to mother up (one trial site only), acute pain related behaviours at 5, 20, 35 and 50 min, and postures at 10 min intervals from 60 to 180 min were recorded. NNLA lambs tended to mother up more quickly than Ring lambs (P = 0.09), and more slowly (P = 0.07) than Sham lambs. Acute pain behaviours were significantly more frequent in Ring and NNLA than Sham (P < 0.001) from 5 to 50 min. NNLA was significantly lower than Ring at 5 min (P < 0.001) and 20 min (P = 0.001). Ring and NNLA did not differ at 35 or 50 min. Abnormal postures were higher in Ring and NNLA than Sham at 60, 70, 80, 90 and 150 min (P < 0.048). Ring and NNLA did not differ at any time point between 60 and 180 min. Delivery of lignocaine with the Numnuts® instrument improved welfare outcome of lambs during the acute pain response caused by castration and tail docking with rubber rings.

Preliminary Findings on a Novel Behavioural Approach for the Assessment of Pain and Analgesia in Lambs Subject to Routine Husbandry Procedures

Simple Summary

The identification and assessment of pain in sheep are important but, due to their stoic nature, are difficult. In the present study, we evaluated the use of qualitative behavioural assessment to assess pain in lambs caused by routine husbandry procedures performed at lamb marking (ear tagging, castration, mulesing, and tail docking). To do this, video footage of control lambs and of lambs subject to these procedures that were either administered analgesics (Tri-Solfen and meloxicam) or a placebo, was captured 1.5 h post-procedure and assessed by 19 observers. Results showed that the observers agreed in their assessment of the lambs and, as expected, the pain caused by the husbandry procedures altered the behavioural patterns and demeanour of the lambs in a way that was captured by observers using this approach. At the time of assessment, it also appears that the analgesics administered did not reduce the pain experienced by those lambs that received them. These results suggest that qualitative behavioural assessment may be useful in identifying pain in lambs; however further work is needed to test this methodology with lambs given effective analgesic pain relief.

Abstract

The identification and assessment of pain in sheep under field conditions are important, but, due to their stoic nature, are fraught with many challenges. In Australia, various husbandry procedures that are documented to cause pain are routinely performed at lamb marking, including ear tagging, castration, mulesing, and tail docking. This study evaluated the validity of a novel methodology to assess pain in lambs: qualitative behavioural assessment (QBA) was used to compare the behavioural expression of control lambs (CONTROL) with that of lambs subject to these procedures that received either a saline placebo 15 min before procedures (PLACEBO), or were administered meloxicam 15 min before procedures in addition to the standard analgesic Tri-Solfen at the time of procedures, as per the manufacturer’s recommendations (ANALGESIC TREATMENT; AT). In terms of behavioural expression, it was expected that: CONTROL ≠ PLACEBO, AT = CONTROL, and PLACEBO ≠ AT. Video footage of the 6−8-week-old lambs (n = 10 for each treatment) was captured approximately 1.5 h postprocedure and was presented, in a random order, to 19 observers for assessment using the Free-Choice Profiling (FCP) approach to QBA. There was significant consensus (p < 0.001) among the observers in their assessment of the lambs, with two main dimensions of behavioural expression explaining 69.2% of the variation. As expected, observers perceived differences in the demeanour of lambs in the first dimension, scoring all lambs subject to the routine husbandry procedures as significantly more ‘dull’ and ‘uneasy’ compared to the control lambs (p < 0.05). Contrary to expectations, the results also suggested that analgesic treatment did not provide relief at the time of observation. Further investigations to validate the relationship between behavioural expression scores and pain are necessary, but these results suggest that painful husbandry procedures alter the behavioural expression of lambs and these differences can be captured using QBA methodology.

Assessment and management of pain in small ruminants and camelids

Many disease processes and management procedures of small ruminants have the potential to result in painful or noxious stimuli. There are a variety of medications and interventions that can be used to minimize the long-term consequences of pain in these species. The first portion of this article focuses on the commonly used medications available for pain management of small ruminants and discusses the benefits and side effects to their use. The second portion of the article focuses on the management of pain associated with common diseases or procedures of these species.

Acute and chronic pain in calves after different methods of rubber-ring castration

The goal of the present study was to evaluate the effect of different methods of rubber-ring castration on acute and chronic pain in calves. Sixty-three 4-6 week-old calves were randomly and sequentially allocated to one of five groups: Group RR (traditional rubber ring castration); group BRR (combination of one rubber ring with Burdizzo); group Rcut (one rubber ring applied with the scrotal tissue and rubber ring removed on day 9); group 3RR (three rubber rings placed one above the other around the scrotal neck); and group CO (controls; sham-castrated). All calves received 0.2 mL/kg bodyweight lidocaine 2%, injected into the spermatic cords and around the scrotal neck 15 min before castration. The presence of acute and chronic pain was assessed using plasma cortisol concentrations, response to palpation of scrotal area, time from castration until complete wound healing, and behavioural signs. Calves of group 3RR showed severe swelling and inflammation, and licking of the scrotal area occurred significantly more often than in groups Rcut and CO. Technique 3RR was discontinued for welfare reasons before the end of the study. All castration groups had significantly more pain upon palpation than calves of group CO, but palpation elicited markedly less pain in group Rcut than in the other castration groups. The most rapid healing time and shortest duration of chronic pain after castration was achieved in group Rcut. For welfare reasons, the Rcut technique should be considered as a valuable alternative to traditional rubber ring castration of calves at 4-6 weeks of age.

Pain in lambs castrated at 2 days using novel smaller and tighter rubber rings without and with local anaesthetic

Without effective pain relief, rubber ring castration of lambs is acutely painful and can also produce chronic pain. The potential of novel, smaller rubber rings to reduce this pain substantially has been investigated. Three groups of eight 2-3 day old lambs, were castrated either with conventional rubber rings (cRR), or novel smaller rubber rings without (nRR) and with local anaesthetic treatment (nRR+La). Behavioural responses and chronic lesions indicative of pain were compared. No major reductions in behavioural responses were produced by castration with nRRs compared with cRRs, but injection of local anaesthetic did reduce these responses significantly. Lambs in all groups developed chronic inflammatory lesions but behavioural evidence of chronic pain was rarely seen. After 28 days, 6/8 necrotic scrotums had been shed by nRR+La; 4/8 by nRR and 2/8 by cRR lambs. The dimensions of rubber rings on necrotic scrotums, suggest that cRRs contracted to their un-stretched size before being shed, whereas nRRs did not. It is concluded that neither of these rubber rings exerted sufficient pressure on trapped nerves to produce anaesthesia rapidly and this may be explained by the physical properties of the tissues at the neck of the scrotum which support the ring.

Effect of age at castration on behavioural response to subsequent tail docking in lambs

OBJECTIVE

To investigate the effects of age at castration on the subsequent behavioural response to tail docking.

STUDY DESIGN

Randomised prospective blinded experimental study.

ANIMALS

Forty-five male lambs were admitted to the study at birth.

METHODS

The lambs were allocated into two groups for castration by rubber ring at 1 (1D, n = 20) or 10 (10D, n = 25) days of age. Following castration both groups of lambs were tail-docked by rubber ring at between 26 and 34 days of age. Their behavioural responses to tail docking were recorded by video for 30 minutes before (n = 11) and 30 minutes after (n = 45) tail docking. Statistical differences were tested using anova with Mann-Whitney post-hoc testing.

RESULTS

Two data sets were removed resulting in n = 19 and = 24 at 1D and 10D, respectively. A significant increase in the incidence of active and abnormal postural behaviour was seen in both groups after tail docking. Three behaviours were significantly different (p < 0.05) between the two groups. These behaviours were rolling, standing unsteadily and the total proportion of time standing with abnormal posture. These behaviours all had greater incidence in the lambs castrated at 1D of age.

CONCLUSIONS

Lambs castrated at 1D appeared to perceive a greater intensity of pain after subsequent tail docking than lambs castrated at 10D.

CLINICAL RELEVANCE

The timing of a single noxious stimulus in young animals can affect subsequent pain perception.

The assessment of emotional expression in dogs using a Free Choice Profiling methodology

This study explores the use of Free Choice Profiling (FCP) methodology for the qualitative behaviour assessment of emotional expression in the domestic dog (Canis familiaris). Qualitative behaviour assessment is based upon the integration of many pieces of information that in conventional quantitative approaches are recorded separately or not at all. Observers are asked to focus on an animal's interaction with its surrounding environment, and to describe the animal's expressive demeanor, or ‘body language’. A specific characteristic of FCP methodology is that it allows observers the freedom to devise their own descriptive terms, and then to use these personal terms to quantitatively score observed subjects. Application of FCP to qualitative behaviour assessment in animals was originally tested for pigs, and more recently for dairy cows, horses, and ponies. The goal of this study was to apply FCP to the domestic dog, and to investigate the inter-observer reliability of assessments of emotional expression in 10 individual Beagles by a group of 18 untrained observers. The data was analysed using Generalised Procrustes Analysis (GPA), a multivariate statistical technique associated with FCP. The observers achieved highly-significant agreement in their assessments of the dogs’ expressions, thereby establishing the applicability of this methodology for the first time in the domestic dog.

Castration of lambs: a welfare comparison of different castration techniques in lambs over 10 weeks of age

Seventy male lambs over 10 weeks of age were castrated using Burdizzo, rubber rings, or surgery to assess the acute and long-term effects of castration. All castrations were performed under local anaesthesia. The surgically castrated lambs were additionally sedated with xylazine and the sedation reversed with tolazoline. The frequency of abnormal postures and immediate behavioural responses indicated that surgically castrated lambs were most distressed; the lambs castrated using Burdizzo and rubber rings were not dissimilar to those of the control group. Between 1.5 and 9h after castration, signs of pain and distress were at a lower level in lambs anaesthetised with bupivacaine compared with those treated with lidocaine. Due to the markedly faster wound healing, Burdizzo castration seemed to be preferable (fewer signs of long-term pain) when compared to the rubber ring technique. It was concluded that local anaesthesia with bupivacaine, followed by the Burdizzo method is the preferable technique for the castration of lambs older than 10 weeks of age.

The welfare significance of the castration of cattle: a review

Castration is an ancient husbandry procedure used to produce docile cattle for draught work, to reduce unwanted breeding, and to modify carcass quality. All the physical methods used to castrate cattle have side-effects and cause pain. The plasma cortisol response to castration using Burdizzo clamps and, by inference, the acute pain experienced, is less than that caused by surgical, rubber-ring or latex-band castration. The cortisol response may be influenced by the age of the animal castrated, but this has not been well defined. Local anaesthesia virtually eliminates the cortisol response, and thus the acute pain, caused by rubber-ring or latex-band castration, but needs to be combined with a systemic analgesic such as the non-steroidal anti-inflammatory drug ketoprofen to eliminate the cortisol response to Burdizzo or surgical castration. When used alone, ketoprofen sometimes reduces the cortisol response to Burdizzo or surgical castration but may need to be accompanied by local anaesthesia to eliminate the pain-induced behaviour seen during the castration process itself. Thus, pharmacological methods are available to virtually eliminate the acute pain experienced by calves during the 12 h following castration. The use of these methods is an additional cost for farmers and may be limited by the availability of drugs for farmers to use and the scarcity of veterinarians in farm animal practice.

Influence of local anaesthesia on pain and distress induced by two bloodless castration methods in young lambs

To assess short- and long-term effects of bloodless castration methods with and without local anaesthesia, behavioural and cortisol responses of lambs were used as indicators of pain and distress. Seventy lambs, aged 2-7 days, were control-handled or castrated by Burdizzo or rubber ring methods with and without local anaesthesia. Either 5 mL of diluted lidocaine (4 mg/kg) or physiological sodium chloride solution was distributed in both spermatic cords and the scrotal neck. The serum cortisol response was monitored for 48 h, and behavioural and clinical traits were followed for three months. Local anaesthesia tended to reduce behavioural and cortisol responses after Burdizzo castration and provided a significant reduction after rubber ring castration. Prolonged pain after rubber ring castration with anaesthesia was not evident. If combined with local anaesthesia, both the rubber ring and the Burdizzo methods are acceptable methods for castration of lambs up to one week of age.

Differences in the acute pain responses of two breeds of lamb following castration and tail docking with the rubber ring method

Charolais × and Suffolk × Mule lambs of less than one week of age were castrated and tail docked using a standard rubber ring technique. After these procedures, their behaviour was monitored for I h. Their respiration rates and scrotal sac measurements were also recorded. Both breeds of lamb exhibited abnormal behaviour patterns following these procedures. The recumbent behaviour pattern of both breeds was remarkably similar but their standing behaviour differed markedly. The Charolais × lambs were significantly more active and had significantly higher respiration rates compared with the Suffolk × lambs. They also took a greater amount of time to recover to a normal posture. Their abnormal behavioural responses suggested that both breeds of lamb experienced acute pain following castration and tail docking, but the type of behaviour exhibited was breed-dependent. The findings suggest that different breeds of lamb may experience different levels of distress in response to the same husbandry procedure. Alternatively, they may simply reflect a difference in the character and temperament of the breeds studied.

Randomised, controlled field trial of two new techniques for the castration and tail docking of lambs less than two days of age

Two methods to reduce the pain associated with the castration and tail docking of lambs with rubber rings were tested by 10 shepherds, each using 60 housed lambs. In 20 of the lambs the innervation to the scrotum, testes and tail was crushed with a 'Big Nipper' bloodless castrator, and in 20 local anaesthetic (2 per cent lignocaine with adrenaline) was injected with a newly developed high-pressure jet injector under the rubber rings after they had been applied; 10 lambs were given a placebo treatment and 10 were treated by the shepherds' routine elastrator ring procedure. Both new methods significantly decreased the incidence of limb and tail movement by 78 per cent and the time spent by the lambs in abnormal postures, when compared with either the shepherds' routine treatment or the placebo treatment. An experienced observer and most of the shepherds also assessed that the lambs suffered signficantly less pain when treated by the two new methods than when they were treated with rubber rings alone. No detrimental long-term effects of the two new methods were observed. On average the new methods took 68 seconds to apply, compared with 29 seconds for the rubber rings; of the two new methods most shepherds preferred using the pressure jet injector.

Evaluation of a short duration behaviour-based post-operative pain scoring system in rats

We have recently demonstrated dose-related analgesic-induced reductions in the occurrence of 7 behavioural activities following midline laparotomy in rats. For these behaviours to be useful in evaluating pain in laboratory rats they must be shown to occur after different types of surgery, and frequently enough to allow rapid scoring of animals. Here, the relevant behaviours were used to test the analgesic efficacy of meloxicam with a variation of our previous laparotomy model. As part of an unrelated project, 57 male Fischer rats were divided into groups to receive either saline (0.2 ml/100g s.c.), meloxicam (0.5, 1 or 2 mg/kg s.c.) or carprofen (2.5, 5, or 10 mg/kg s.c.) 1h before surgery. Behaviour data were collected for 10 min following 25 min of recovery from isoflurane anaesthesia. The cumulative frequencies of back arching, fall/stagger, writhe and poor gait were used to compute a composite behaviour score. Irrespective of whether analyses included only 5 or all 10 min of the observation period, the relevant behaviours occurred significantly more often in rats given saline or low dose meloxicam than in those given 1 or 2 mg/kg of meloxicam, or any dose of carprofen. We conclude that this technique of quantifying post-surgery behaviour is an effective pain scoring method following abdominal surgery in rats, and that 1 mg/kg meloxicam significantly attenuates laparotomy induced pain. Since only a short observation period is required, this approach represents an important practical advance in assessing abdominal pain severity and clinical drug potency.

Evaluation of Welfare State Based on Interpretation of Multiple Indices

Welfare is a multidimensional construct and its quantification is of major scientific, societal and economic importance in veterinary medicine. The construction of indices that measure welfare validly and reliably remains a considerable challenge. A general methodology for constructing welfare indices can be adapted from human medicine (in particular, from methodologies to assess Quality of Life [QoL]) and modified to reflect the fact that all assessments of animal welfare must be observer-based. The methodology is based on the creation of individual, composite indices for distinct dimensions/domains of welfare such as pain, disease, or stress. The domains include behavioural, physiological and biochemical markers. We have established QoL methodologies in the assessment of acute and chronic pain in dogs and generalised this approach to farm animal welfare. We describe the development of a questionnaire with seven behavioural categories which are used to create a single pain score to assess acute pain in dogs. For chronic pain in dogs, a structured questionnaire with over 100 items has been devised, which the owner completes by indicating degree of agreement with each item using a seven-point Likert scale. The welfare measure includes pain as an integral component as well as husbandry, behavioural and physiological/biological measures. In each case, a profile of the individual indices can be studied and compared over time or among observers. These indices may also be combined to form a single composite welfare measure, should this be appropriate, using scaling models. In the welfare setting, we have both causal and indicator variables — and indeed, for farm animals, the causal variables may be sufficient cause for poor welfare (eg the presence of disease or inadequate husbandry).

Assessing Pain in Animals

Assessing the experience of pain in animals is a difficult task, yet one that is important in animal welfare research. Some approaches to pain assessment in animals are reviewed here. General qualities of pain scales and specific parameters suitable for clinical and experimental pain assessments are discussed. It is argued that pain assessment will progress through an integration of objective and subjective observations of behaviour coupled with multiple measures in various other areas. Such multidimensional pain scales allow an adequate characterisation of the complexity of an individual animal's pain experience to be made. This knowledge improves the recognition and treatment of pain and will allow informed moral debate on the acceptability of practices such as castration and tail-docking of lambs.