July 15, 2014
This peer-reviewed summary has been prepared by the American Veterinary Medical Association Animal Welfare Division. While principally a review of the scientific literature, it may also include information gleaned from proprietary data, legislative and regulatory review, market conditions, and scholarly ethical assessments. It is provided as information and its contents should not be construed as official AVMA policy. Mention of trade names, products, commercial practices or organizations does not imply endorsement by the American Veterinary Medical Association.
Piglets may undergo a battery of procedures during the first few days or weeks of life, potentially including tooth-clipping, tail docking, castration, and ear-notching or another identification method such as tagging or tattooing.1 Each of these procedures involves a degree of tissue damage potentially resulting in the piglet experiencing pain. As it is generally accepted that pigs experience pain, and pain compromises welfare, it would be desirable for these procedures to be refined or replaced with practical alternatives, so long as this results in a net benefit to the animal. The corresponding background information of teeth clipping, tail docking and identification is grouped together because strategies such as reduced invasiveness, analgesia and anesthesia, and replacement are common themes requiring consideration for each procedure. While some procedures (such as identification techniques) have received relatively little research attention, general findings, such as which analgesics are safe and effective for use with unweaned piglets, may be broadly applicable.
Piglet teeth clipping
Piglets are born with outwardly projecting canine or “needle” teeth used in competition with littermates for teat access. These teeth can be blunted or shortened during the first week of life by grinding the tip, clipping the tip, or clipping the tooth at the gum line.
Litters of piglets with intact needle teeth suffer more facial lacerations,2,3,4,5,6,7,8 and their sows may have more lacerations on their udder4,8 and may shield their teats by spending more time lying on their bellies.4 Piglets whose teeth have not been clipped may sometimes suffer higher rates of mortality due to increased overlying and crushing by the sow; it has been suggested this might be due to sows being injured and becoming more restless. 4 However increased udder injury is not always found when piglets are left intact,8 and it has also been suggested that piglets whose teeth have not been clipped are less competitive and so lie closer to the sow thus increasing their risk of being crushed.8 Recently, a study found that unclipped teeth and undocked tails did not have significant negative effects on average daily gain (ADG), gain to feed ratio (G:F), serum immunoglobulin G (IgG) concentrations, mortality rates, wound severity/incidence, post-weaning behavior of piglets or carcass composition.9 These studies could suggest that there is little to no significant advantage to the clipping of teeth.
Clipping has been shown to increase behaviors suggestive of discomfort such as “chomping.”5 Piglets whose teeth have been clipped may experience more gum and tongue injuries4,8 and potentially painful inflammation or abscesses of the teeth.10,11 These injuries may lead to infections and increased time spent sleeping4 (seen as an indicator for infection).
Reduced Severity—Clipping off the tip of the tooth has similar benefits to clipping to the gum line.12
Technique—Some studies find that grinding causes more damage8 and distress13than clipping, while others found clipping to be more damaging.6 Equipment maintenance and staff proficiency may be more important than the type of equipment used.
Clipping is now often carried out selectively on individuals or litters demonstrating or predisposed to injuries. Clipping only as required can save time and labor costs, but involves clipping some teeth at a later age.1,14 Routine clipping may be easier to forego when working with more placid breeds14 and when larger litter sizes are avoided.14,15
Clipping, properly performed, rarely produces significant changes in growth rate,4,7 weaning weight8,7 or mortality.4,7 It is performed primarily to reduce animal discomfort and poor appearance due to lesions; however, tooth resection also causes discomfort and potential infection due to opening of the pulp cavity. Routine preventive teeth clipping is reportedly becoming less common.1,16
Piglet tail docking
Tail biting causes physical damage and fear in recipient animals.22 Tail-bitten pigs are also more likely to exhibit pleuritis (inflammation) and lung abscesses17 and their carcasses are more likely to require trimming.17 Tail injury may18,19or may not20,22 effect growth or mortality depending upon severity.
Tail docking reduces the incidence and severity of tail injury. Tail docking also helps control tail biting behavior, though it does not treat the underlying causes. The incidence of preventive tail docking is hard to establish. A survey of supermarkets conducted in the UK in 2007 provided an estimate that 88% of pigs were tail docked—although tail docking is permitted in the UK only when tail biting is a problem and not as a routine precaution.21
Tail-docked pigs have been found to have fewer tail injuries22,23 and indications of better immune function.22
Tail docking causes physiological and behavioral responses indicating acute stress when performed on six-day-old pigs.24 These include increased blood cortisol concentrations, reduced white blood cell count and increased sitting and scooting behavior. The cortisol response does not occur when tail docking is performed with a cautery iron.24,25 Docked tails may develop neuromas, which are associated with increased sensitivity to pain.26
Considerations: Causal Factors
Outbreaks of tail-biting behavior are complex, with many contributing factors. There is an inherited component in some breeds associated with lean carcass traits.27 Pigs are more likely to be bitten if they have an undocked tail,28 hold their tail between their legs,29 or are male.17,30 Males may be more frequently bitten when housed with females,31 but other studies suggest that mixed-sex housing reduces the incidence of biting overall.28
Although tail biting does occur in outdoor systems,31 it is generally less common in outdoor housing22 or indoor housing with natural ventilation.28 Provision of solid floors35 and straw28,35,32,33 reduces the incidence of tail biting.
Schmolke et al did not find that group size (10 to 80 pigs) affected rates of tail biting.34 However, in general terms, tail biting is more likely to occur with high stocking densities and increased numbers of pigs per feeding space.28,35
Once tail biting has begun to occur it may continue and intensify due to attraction of pigs to the smell and taste of blood.36,37
Tail docking with a hot iron was found to cause more distress and neuroma formation and so it is not an effective refinement of technique.13
Tail docking is performed to prevent peer-inflicted injury to the tail that can become severe. Because docking causes pain and stress, it should be performed as early as possible and/or in conjunction with appropriate analgesia.38 The ideal welfare outcome would be for tail biting to be reduced to a level where tail docking need not be carried out routinely, if at all. Although tail biting has a complex etiologic basis some researchers believe that improved environmental design is the most promising approach to reduce biting and reduce or eliminate the need for docking.39 Changes in the swine market, producer subsidies, and enrichment-material requirements could also encourage swine producers to explore and implement new practices to reach this goal.40
Piglet identification methods
Pigs need to be individually identified throughout life for management and traceability of products for safety or assurance schemes.41,42
Ear notching is considered to be painful.43 Due to the increased labor and time required to apply the ear notches and read them, this procedure is not commonly used in commercial settings. Ear notching is mostly used by small purebred breeders and 4-H pig breeders. Producers that do utilize ear notching, with or without tail docking, may limit resource expenditure by delaying these procedures briefly.44 This may cause additional discomfort to the animals, but fewer animals of lower birth weight may survive to this point and fewer procedures would then need to be carried out.
Ear tags may carry a visual number and/or and electronic transponder.41
Small transponders may be injected beneath the skin at the base of the ear36,45,46 or intra-peritoneally. Injected transponders may result in inflammation or infection in some cases.41 Larger transponder size may cause more severe reactions.41,47 Large transponders positioned at the base of the auricle also have a higher rate of loss, possibly because of inadequate application with insufficient needle penetration leading to a transponder that remains near the application point, facilitating its loss.40,46,48
Pigs may be tattooed with an identifying number.49Tattooing causes stress in pigs, which may be reduced by refinement of equipment and techniques.50
Individual animal identification is desirable for tracking and ensuring good care. There has not been a comparison among identification systems on the basis or pain and other welfare parameters, and this should be included as part of an ongoing refinement process. Ultimately non-invasive methods such as biometric identifiers or DNA tracking may become available.51,52
Most invasive procedures performed on piglets are done to protect the welfare of the pigs rather than to improve production.53 However, many of these procedures are widely considered to be painful for swine and the development of refinements and alternatives is desirable. Prophylactic removal of teeth, and to some extent tails, is becoming less common as less invasive alternatives become available. Where procedures that cause pain are still necessary, the use of analgesia and/or anesthesia should be encouraged wherever this is of net benefit to the animal.
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