Pain Control26 July 2013
A thorough review of the anaesthetic and analgesic options currently available to the pig industry by Robert Friendship (University of Guelph) and George Charbonneau (Southwest Veterinary Services, Stratford Ontario), presented at the 2013 London Swine Conference.
It is generally agreed that all mammals experience pain in a similar manner to humans. Some species such as pigs attempt to hide the effects of pain. Possibly in the wild this behaviour was protective, because a pig showing signs of pain might attract the attention of a predator. Therefore, one problem in minimising pain in pork production has been the difficulty in detecting pain and assessing the severity of the pain.
A second challenge has been the scarcity of products licensed for use in food-producing animals that are effective in treating pain. This area of medicine has expanded greatly over the past decade but the pharmacological options approved for use in swine are still very limited. There are other potential reasons that have limited the advancement of pain control in the pork industry including economics and labour requirements. On the other hand, there are important reasons why we need to carefully examine this issue and determine where there are opportunities to improve pain control. In certain areas, pain management might improve productivity but more importantly, an on-farm programme to minimise pain will be considered part of responsible animal husbandry by the general public.
A report1 from the French National Institute for Agricultural Research expert panel on pain in food-producing farm animals published in 2012 advocated using “the 3 S approach”. The 3 S’s refer to suppress, substitute and soothe.
Under the “suppress” category, they suggested that a first step would be to review a farming operation and eliminate any source of pain that brings no obvious advantage to the animals or the producers as well as sources of pain for which potential benefits are largely exceeded by the negative effects. Secondly, “substitute” refers to identifying a painful but necessary procedure and replacing it with a technique that is less-painful. And thirdly, “soothe” refers to administration of pain medication where appropriate.
There are opportunities on every farm to improve animal welfare and possibly increase productivity by carefully considering the 3 S approach. Unfortunately, the topic of pain associated with pig farming has been sensationalised by various groups who generate revenue through propaganda. This creates an environment of distrust and defensiveness that is counter-productive.
In this presentation, the authors aim to have an open and frank discussion to explore how as an industry we can implement improvements in pain control and how we might move forward with continuous assessment and change as techniques are developed to ease pain in livestock.
Examples of the 3s Approach
On most farms at first glance, there does not appear to be anything obvious that is done that creates pain that is not necessary or beneficial but maybe, if everyone spent time carefully reviewing management procedures, examples will be found. For example, a large number of farms have discontinued clipping needle teeth. For the most part, removing the sharp tips of needle teeth provides a benefit in reducing cuts and possibly minimising the occurrence of greasy pig disease but there are farms where the number of damaged gums and broken teeth outweighs the positive benefits. It is something that needs to be evaluated on each farm. Rather than eliminating a procedure like needle teeth clipping, a better solution might be to improve the technique or possibly replace the old side-cutters that are being used.
“The times, they are a changing!” All stakeholders need to face the fact that expectations are changing. Two decades ago, it was common practice to castrate 90kg-plus boars after they completed record of performance testing. This was done on most farms without any anaesthetic or analgesic. Post-surgical infection was not uncommon and excessive areas of trim were a problem at the processing plant. Almost anyone would have agreed at the time that this did not seem right but the practice continued. The industry came together, in the absence of public pressure, and decided that this practice could no longer be justified based on animal welfare implications. The cost of marketing these animals as intact boars was absorbed as part of cost of production.
Over the past few decades, the swine industry recognis-zed that castration appears to be more painful when performed on older animals and so has substituted castration of pigs under 10 days of age for the more painful traditional practice of castration of weaned pigs. Likewise, on many farms, there has been a lot of thought put into moving pigs. For example, better design of loading areas has eliminated or reduced the use of prods and minimised pig injury.
This is an area that hopefully will develop further over the next few years as new products become available to relieve pain.
There are several categories of drugs that can be of use in reducing pain and stress. In general, there are drugs that tend to block all pain sensation, the anaesthetics (general and local), and there are drugs which suppress pain, often referred to as analgesics or pain killers. There are drugs that primarily reduce inflammation, which is a major source of discomfort - for example, corticosteroid drugs.
In general, the swine industry needs to consider incorporating the judicious use of anesthetics and analgesics into standard operating procedures as a way of improving welfare.
Pain Management Expectations
Pain is defined as an unpleasant sensory and emotional experience that is associated with actual or potential tissue damage.2 Procedures that are potentially painful include tooth clipping, tusk removal, ear notching, tail docking, castration, scrotal hernia repair, abdominal hernia repair, Caesarian section, vasectomy and epididymectomy. The use of anaesthetic or analgesic prior to routine procedures creates a logistical problem and increases labour costs. Pigs must be visited multiple times for one procedure.
Other conditions that are apparently painful include vaginal prolapse, rectal prolapse, fractures, arthritis, infections, bitten tales, bitten vulvas, shoulder sores, lacerations and contusions. Where these conditions are caused by deficiencies in the safety of the facilities or management problems, every effort should be made to correct the problems as soon as possible so that pain can be prevented.
The Canadian Veterinary Medical Association (CVMA) holds that castration of piglets to prevent aggression and boar-taint in post-pubertal boars is a painful procedure at any age. The CVMA recommends that, “when castration of piglets is required, it should be performed between the ages of three to seven days with the use of appropriate analgesia. Non-surgical methods of controlling boar taint should be considered as technology develops.” These technologies could include marketing of light weight intact males but this may be cause a reduction in consumer demand. Immunocastration with Improvest® is another alternative.
A survey published in the Canadian Veterinary Journal in 2007 concluded that “veterinarians needed to give more consideration to pain management in livestock” and the authors further indicated that “the cost of pain relief in food animals should be incorporated into current food policy rather than remaining one of the many extrinsic costs of food provision.”3
Although it is relatively easy to make these pronouncements, it is difficult for producers or processors to pass these additional costs along to the consumer and profit margins are already very tight.
Pain Relief Tools
There are a wide variety of anaesthetic and analgesic medications that are available for veterinary use.
An ideal anaesthetic or analgesic must be effective, safe and practical. Measurement of cortisol levels, vocalisation, trembling and suckling behaviour can be used to measure a reduction of pain. Off-label use of approved products with a Drug Identification Number (DIN) and compounded products present meat residue questions. Anaesthetics may make the pig drowsy and susceptible to trauma or crushing by the sow. Intravenous medications are impractical for routine procedures due to the difficulty of performing intravenous injections. Intramuscular, subcutaneous and oral medications are much easier to work with.
The question of cost-effectiveness always arises. Arguments based on cost of pain control usually fall on deaf ears when it comes to explaining these constraints to consumers or society in general.
Anaesthetics – general – thiopental e.g. Thiotol® (Label) (IV): An ultrashort acting barbiturate. Perivascular injections are painful. Causes some respiratory depression; a poor muscle relaxant and a poor analgesic. Pre-operative and post-operative analgesic is recommended. A narcotic and is therefore a controlled drug. There is no withdrawal period on the label indicated for thiopental. However, if thiopental was to undergo the approval process today, the lack of depletion profiles, MRLs and human safety data would make it difficult to determine that the zero withdrawal is appropriate given that it is cleared from the system by depositing in fatty tissue.
Anesthetics - general – ketamine e.g. Ketaset® (Off label) (IM/IV): A dissociative anaesthetic that is not licensed for food animals in Canada. Not compliant with Canadian Quality Assurance guidelines. Useful for surgical procedures such as vasectomy, epididymectomy when boars will not be directed to the food chain. Some issues with respect to human abuse and therefore must be strictly controlled. No withdrawal information for food animals.
Anaesthetic – general – carbon dioxide (Off label) (Inhaled): Carbon dioxide is being used in some European Union countries. There is a measurable reduction in pain response. The product does, however, result in increased death loss associated with the procedure. No withdrawal.
Anaesthetic – local – lidocaine e.g Lurocaine® (Label) (IM/SQ): Used for regional infiltration, epidurals, intra-testicular infiltration with diffusion into the spermatic cord.4 Often used in combination with a sedative in order to reduce stress and struggling during restraint. The withdrawal is five days.
NSAID – flunixin e.g Banamine® (Label) (IM): Label claim for flunixin in Canada for a reduction of fever in pigs with respiratory disease but like most Non-steroidal Anti-inflammatory Drugs (NSAIDS), flunixin does have good analgesic properties when used peri-operatively and for chronic musculoskeletal conditions. IM injection can cause some local tissue irritation. Flunixin has been shown to decrease plasma cortisol and pain induced behaviour when administered before castration in four- to six-day-old piglets.5 The withdrawal is 13 days.
NSAID – ketoprofen e.g. Anafen® (Label) (IM): Label claim for reduction of fever and inflammation associated with respiratory infections. This product does an excellent job of reducing fever. Young piglets may have lower peak plasma concentrations than older piglets. Can be used as a peri-operative analgesic. The withdrawal period is seven days.
NSAID – acetaminophen e.g. Pracetam 20%® Tylenol® ( Label) (Oral): Label claim is for relief of fever and associated clinical symptoms in acute respiratory disease. Acetominophen has some analgesic properties but generally less than some other NSAIDs.6 Uptake through the digestive tract is greater than 90 per cent. The withdrawal is three days.
NSAID – acetylsalicylic acid e.g. ASA boluses®, Aspirin® (Off label) (Oral): Approved for cattle. In other countries, this product is recommended for the reduction of fever in pigs. ASA has weaker analgesic properties than some other NSAIDs and is less effective in reducing perioperative pain. High doses (e.g. 100mg per kg) reduce fever in pigs.6 No label withdrawal for cattle but because of the association with Reye’s syndrome in children, the Canadian global Food Animal Residue Avoidance Database (CgFARAD) policy recommends at least a 24-hour withdrawal.
NSAID – meloxicam e.g. Metacam® (Off label) (IM): Approved in cattle but not in swine. Has a European Union label claim for anti-inflammatory and analgesia including non-infectious locomotor lameness. Pre-castration administration of meloxicam in four- to six-day-old piglets significantly reduce plasma cortisol levels and decreased pain associated behaviour for one to four hours when compared to negative control piglets.2,7
Corticosteroids – isoflupredone e.g. Predef 2X®(Label) (IM): Labelled for alleviation of pain and lameness associated with generalised and acute localised arthritis. The withdrawal is five days.
Corticosteroids – dexamethazone e.g. Dexamethasone 5® (Off-label) (IM): Analgesia is associated with the anti-inflammatory effect. No label withdrawal available for swine.
Sedatives (they are not analgesic)
Sedatives – azaperone e.g. Stresnil®(Label) (IM): Fast onset within 10 minutes. Provides no analgesia and therefore not suitable for use by itself for surgical procedures. Can be used in combination with a local anesthetic and as a premedication for thiopental for surgical procedures. The withdrawal is one day.
Sedatives – acepromazine e.g. Atravet® (Label) (IM): Variable onset and effectiveness. Provides no analgesia and therefore not suitable for use by itself for surgical procedures. Can be used in combination with a local anesthetic and as a pre-medication for thiopental for surgical procedures. The withdrawal is seven days.
Sedatives – xylazine e.g. Rhompun® (Offlabel) (IM/IV): An alpha-2 agonist licensed for cattle. Provides good analgesic properties. Xylazine is commonly used in combination with ketamine for minor surgeries and this produces a good combination of anesthesia and analgesia. No withdrawal information for swine available.
Euthanasia provides pain relief that is absolute. As part of the Canadian Pork Council Animal Care Assessment, all farms have specific, age-appropriate methods for humane euthanasia in place and these are clearly stated in the farm euthanasia plan.
What is less clear on most farms is exactly how the decision is made with respect to timeliness of euthanasia. This option must be considered where prolonged pain control is impractical and animals should not be transported to market.
Summary of Some of the Research Initiatives at Guelph
Three studies were carried out on a 600-sow commercial farm and involved 997 litters and 4,379 piglets by Ryan Tenbergen (MSc student).
- A study was conducted to determine the effect of minimising post-farrowing pain by routine injection of an analgesic after farrowing was complete. Sows were either given an IM injection of meloxicam (Metacam®, Boehringer-Ingelheim Ltd.; 0.4 mg/kg of bodyweight; n=149) or a similar volume of a placebo (n=140) after farrowing. There were no significant treatment effects for piglet weight gain or mortality. Studies elsewhere have shown that treatment with pain-killers to sows that had a difficult farrowing or were sick (MMA) results in improved productivity.
- A study was performed to determine if the same pain killer (meloxicam) could be used to minimise the pain associated with processing piglets, i.e. castration and tail-docking. Both male and female piglets were alternately allocated to receive a single IM injection of 0.4 mg/kg of bodyweight of meloxicam (n=1,427) or a placebo (n=1,461) at least 30 minutes prior to processing. Mortality and growth rate were monitored and treatment was found to have no effect. Castrated piglets receiving meloxicam displayed significantly less tail-jamming behaviour and tended to exhibit less isolating behaviourthan piglets receiving the placebo. These behaviour results suggest meloxicam did reduce pain. Likewise, plasma cortisol, which rises when animals are stressed or suffer pain, was higher in the piglets receiving the placebo compared to the meloxicam treated piglets for the first few hours after castration.
- A second piglet study was performed to evaluate a different pain killer, ketoprofen (Anafen®, Merial Canada Inc.). This study involved 1,491 male piglets, which were alternatively to receive either ketoprofen (3mg per kg of bodyweight; n=755) or similar volume of a placebo (n=736) at least 30 minutes prior to processing. Results were similar to the meloxicam study, with no difference in growth rate and mortality between pigs receiving a pain-killer and those pigs receiving the placebo but behaviour and cortisol levels suggested a positive reduction in pain during the first few hours after castration.
Another study was carried out by MSc student, Michelle Lam. She evaluated the use of a local anaesthetic (lidocaine) injected into the testicle to reduce the pain associated with castration. She also looked at the combination of freezing the testicle and spermatic cord with lidocaine, and using a pain-killer, meloxicam. The local anaesthetic helped block the acute pain caused by severing the spermatic cord and removing the testicle, and the combination lidocaine and meloxicam helped reduce behavioural changes up to 24 hours after castration. The negative aspects of this approach were that the animals had to be handled twice because the freezing needed about three minutes to take effect and lasted for about an hour, and testicular injections did cause some discomfort.
Progress in animal welfare, including pain management, is being made. Implementation and improvement will require continuous reassessment of management and an awareness of new developments.
1. Guatteo R. et al., 2012. Minimizing pain in farm animals: the 3S approach – ‘Suppress, Substitute, Soothe’ Animal 6:8, 1261-1274.
2. Lemke K.A. 2004. Understanding the pathophysiology of perioperative pain. Canadian Vet. J. May 2004; 45(5):405-413
3. Hewson C.J., Dohoo I.R., Lemke K.A., Barkema H.A. 2007. Canadian Veterinarians use of analgesics in cattle, pigs, and horses in 2004 and 2005. Canadian Vet. J. Feb 2007; 48(2):155-164
4. Ranheim B., Haga H.A., Ingebrigsten K. 2005. Distribution of radioactive lidocaine injected into the testes in piglets. J. Vet. Pharmacol. Ther. Oct 2005; 28(5):481-483.
5. Langhof R., Zols S., Bars A., Palzer A., Ritzmann M., Heinritzi K. 2009. Investigation about the use of analgesics for the reduction of castration induced pain in suckling piglets. Berl. Munch. Tierarztl. Wochenschr. September October 2009; 122 (9-10):325-332.
6. Salichs M., Sabate D., Ciervo O., Homedes J. 2011. Comparison of the antipyretic efficacy of ketoprofen, acetylsalicylic acid, and paracetomol, orally administered to swine. J. Vet. Pharmacol. Ther. June 14 2011.
7. Zols S., Ritzmann M., Heinritzi K. 2006. Effect of analgesics on the castration of male piglets. Berl. Munch. Tierarztl. Wochenschr. May-June 2006;119(5-6):193-196
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