Overview of Lameness in Pigs
Lameness has been an issue in swine production for many years and continues to be a problem worldwide. Although lameness can be caused by congenital or developmental abnormalities, most lameness in production animals is caused by pain associated with infections, trauma-related injuries, or underlying metabolic diseases. As such, it has become an area of focus for swine farm audits of animal well-being. It is also an economic issue, because an increasing prevalence or incidence of lameness in a herd is likely to affect viability, growth, or reproduction of pigs. Pig flow may be affected if farrowing targets are not met because of high rates of breeding stock removal or if growth of grower/finisher pigs is slowed by high lameness incidence. As with diseases of other body systems, lameness problems in a swine herd require a comprehensive approach if a diagnosis (or diagnoses) is to be reached so that preventive or curative measures can be instituted.
The types and causes of lameness can vary widely by age of the pig and, to a lesser extent, by gender and breed. Traumatic injury can obviously cause lameness in pigs at any age, but some types of lameness arising from infectious or physiologic causes can have a more limited age range or set of circumstances under which lameness develops. It should also be remembered that some infectious agents can affect and cause lameness in multiple species, so understanding the signalment of not only the group of pigs under evaluation, but also other pigs or species recently in contact or proximity with the affected group, is part of the comprehensive approach required for lameness investigations.
In addition to the signalment of the individual pigs in a population, the signalment of the composite group (ie, demographics) is also an important consideration. Examples of group signalment are the proportion of gilts in farrowing groups because gilts are more likely to pass pathogenic bacteria to their progeny, or the herd immune status with respect to a particular pathogen based on, for example, time since the most recent vaccination against erysipelas. Even the relative body condition of sows going into a cold season can predispose populations to increased or decreased susceptibility to herd health problems.
History taking must be thorough and should include information on age of onset, typical clinical signs, and progression of the lameness. Morbidity and mortality associated with any lameness and the number of groups, pens, rooms, or buildings with affected pigs are all relevant. Morbidity information should include treatments and the responses observed. Culling rates can also provide information on morbidity, although recorded reasons for culling sows are notoriously inaccurate. Condemnations at slaughter can be another way to secure objective data on morbidity, when condemnations for limb abnormalities or fractures have a direct bearing on lameness and for polyserositis or downer pigs, which have an indirect bearing on lameness.
Mortality data can be evaluated as an absolute rate or, more usefully, as incidence by stage or week of production. For sows, body condition score at the time of death or euthanasia can help reveal underlying lameness conditions because recorded reasons for cause of death are also prone to inaccuracy, and lame sows tend to lose body condition before death or euthanasia.
The investigation of a lameness problem on a farm also requires an understanding of the operation of the farm itself. The logistics underlying the establishment of the group of pigs under investigation should be explored: the source(s), transport, and placement of the pigs. The history of replacement breeding stock accessions is relevant, especially if new herds of origin or different genetic lines were introduced.
Health program and practices should be considered. It is important to determine whether vaccination or medication protocols were changed. If possible, it is equally important to determine whether protocols were followed correctly. Audits of product consumption or antibody testing for vaccine titers, if available, can be used as verification methods.
Investigating nutrition programs as a possible contributor to lameness problems can become extensive. However, the fundamental questions can be reduced to determining what rations were formulated, mixed, and delivered to the pigs. Problems are relatively rare but possible during each stage of the process. At the formulation stage, lameness problems can result, for example, when book values of phosphorus are different than actual amounts present in the product used, or vitamin D or phytase activities are not at expected levels because of storage, processing, or other issues, which can affect calcium and phosphorus metabolism. At the mixing stage, mills can have time constraints that do not allow adequate mixing of feed batches, so the feed composition can be uneven. At the point of delivery, feed density differences in sow gestation feed can result in over- or underfeeding when volumetric feeders are not adjusted to keep pace with weight and nutrient density changes in the ration.
Experiences with a series of lameness problems collectively referred to as metabolic bone disease—variably concerning problems in calcium, phosphorus, and/or vitamin D metabolism—have put more focus on the need to test feed constituents more thoroughly before inclusion in the diets, to test mixed feed for adherence to the formulation, and to monitor pigs more closely for serum vitamin D levels and bone densities so problems can be detected earlier.
Farm staff have a large role in caring for pigs on farms and, therefore, are a key source of information and possible solutions to lameness problems. Personnel working with the pigs must also be evaluated as possible contributors to lameness problems. Pig handling and movement are obvious potential causes of lameness, so understanding the level of staffing and extent of staff training are important parts of the case history. Observing the interaction between the pigs and the farm staff can help reveal the nature of interactions likely to occur routinely on the farm.
Understanding the farm hygiene practices is important to determine risks of injury and disease from slippery surfaces or contamination from transport vehicles. If bedding is used, determining the sources and management of the bedding is also significant to characterize disease risks.
Finally, the history of diagnostic results for the farm and the area are critically important to have a starting point for further investigation of lameness problems. If possible, the disease history among neighboring farms can help understand disease risks. At a minimum, a review of all the pertinent diagnostic testing results for the specific herd is required.
Diagnosis of lameness can be complex. At least three body systems (musculoskeletal, nervous, and integumentary) may be affected independently or in combination. Because of the different organ systems potentially involved, a consistent and thorough approach to evaluate all components of lameness is essential. When examining a herd with a locomotor problem, the focus should not be solely on a group of affected pigs. Younger pigs should be evaluated to identify potential underlying causes or predispositions to the problem under investigation. Other groups of pigs of similar ages and older pigs housed in other pens or buildings should also be evaluated to determine whether they have similar or different problems. The conditions potentially causing the problem should not be assumed to be restricted to those most often associated with one particular age group.
When evaluating a population of pigs, it is useful to first consider an inverted pyramid approach of the entire room, followed by pens of pigs and finally individual pig evaluations. The entire room evaluation is intended to provide a general sense of the overall health, activity, and behavior of the group. Pen-by-pen evaluations provide an opportunity to make counts or estimates of the prevalence and severity of the lameness. The individual pig assessments are intended to focus on the specific cause(s) of the lameness.
The pen evaluation is intended to identify the lame pigs. Pigs should be made to move around (in pens or into alleyways), to stand, and if housing allows, to walk, watching for behavior typical of lame pigs. The pen ahead and pen behind the last pigs to stand up and first pigs to lie down should be observed. Pigs that take advantage of the diversion caused by the evaluation to access feed or water should be noted. Abnormal gait and posture, body condition (thin pigs are more likely to be lame), and physical evidence of trauma, infection, or malformation (swelling, vesicles, etc) should be watched for in individual pigs.
If an individual pig warrants a more extensive physical examination, some degree of restraint may be required. If less restraint is sufficient, the pig can remain free in a pen or stall, or a sorting panel can be used to prevent the pig from moving away. If more restraint is needed, small pigs can be lifted or manually held for examination. Larger pigs can be snared or cast using ropes. The advantage of this type of restraint is that it immobilizes the pig. Disadvantages are that the pig is placed in an unnatural posture, excess muscle tone is normally stimulated, and help from additional people is usually required.
Anesthesia is another possible means of greater restraint. The advantage is that muscles are relaxed, allowing manipulation of skeletal structures such as potential fractures. Additionally, muscle mass can be assessed, joint taps or other diagnostic procedures can be performed, and more extensive evaluations such as radiography or other scanning are possible if warranted. Disadvantages are the management of controlled substances used as anesthetics, required withdrawal times, and the challenge of managing recovery from anesthesia with other pigs present or in facilities that may not be set up for such procedures.
Some farms may have lift chutes to immobilize boars, sows, and gilts for foot trimming or other procedures. These chutes allow good restraint with full access to the feet and lower limbs, with none of the disadvantages of chemical restraint. However, availability of lift chutes on sow farms is limited.
A general physical examination of an individual pig for lameness requires a thorough, systematic, and consistent process by individual clinicians. One such approach is to proceed from the bottom up and front to back of the pig, ie, the feet are evaluated first, followed by the limbs and torso in a front-to-back progression.
The feet can be examined most easily when the pig is lying laterally recumbent or lifted (manually for small pigs or using a mechanical chute for sows). Standardized guides exist to score foot lesions by type. Prevalence and severity of foot lesions in a sow herd can be estimated by scoring the feet using statistical sampling. Using a good flashlight enhances scoring foot lesions. Feet may need to be cleaned for pigs housed on non-slatted floors. Exploring lesions by trimming with a hoof knife, clipper, or grinder requires adequate restraint and safety protocols. Foot lesions have been well defined but do not always correlate with lameness on an individual pig basis, because the pain associated with foot lesions depends on exposure or infection of the sensitive tissues underlying the claw, heel, and sole of the toes.
Limb and joint palpation and manipulation should also be conducting using a consistent approach. The amount and type of restraint again depends on age of the pig. Cardinal signs of inflammation, ie, heat, swelling, pain, and redness, should be noted. Strength, range of motion, crepitus, and weight-bearing distribution should be evaluated. Joints embedded in muscle mass (eg, hip, stifle, shoulder) require deep palpation, which may not be possible on large, heavily muscled pigs. Fracture of the head of the femur (epiphysiolysis capitis femoris), a common cause of downer sows, is difficult to diagnose antemortem. Because it is buried under a large muscle mass, even infectious arthritis in the stifle, a site commonly affected by Mycoplasma hyosynoviae, can be missed on individual pigs on cursory examination.
The torso can be evaluated and palpated for muscle mass, tone, and symmetry. Ribs should be examined for evidence of fractures or knobby thickening (rachitic rosary), and the spine examined for kyphosis.
A neurologic examination is indicated in cases when neurologic disease is suspected and should be performed in a similar fashion to that for dogs, cows, and horses (see Physical and Neurologic Examinations).
Postmortem examination of lame pigs is often required to reach a definitive diagnosis for a herd lameness problem. Field necropsy of baby, nursery, and grower pigs is relatively easy to accomplish. However, for larger finisher pigs, gilts, sows, and boars, the process is laborious because of the size of the animal and the need to examine numerous joints and bones, often including the spine if appropriate to the clinical presentation. At a minimum, developing expertise in opening joints on dead pigs that may not be ideal candidates for diagnostic sampling can help direct diagnostic efforts when more suitable pigs are available. Examination of greater numbers of pigs improves the odds of accurately characterizing the cause(s) of lameness.
Although on-farm necropsies are feasible, it may be better to submit entire or even live pigs to a full-service diagnostic laboratory. In particular, submitting live pigs to a laboratory allows greater odds of successfully culturing live bacteria, which are needed for antimicrobial susceptibility determination or production of autogenous vaccines. Additionally, diagnostic laboratories have the facilities and personnel to perform more complete and careful dissections of joints, the spine, and brain. This is particularly true of sow lameness problems. For example, an extensive dissection of the pelvis is required to reveal an apophysiolysis of ischial tuberosity in young sows with characteristic dog-sitting posture after farrowing. Likewise, vertebral abscessation can be a common cause of downer sows, and the vertebral column must be split sagittally to make a definitive diagnosis of this condition.
If pigs are to be submitted to a diagnostic laboratory, appropriate pigs must be selected and delivered, accompanied by an accurate history and a list of differential diagnoses. Adequate numbers of representative, acutely lame, untreated pigs are essential.
If tissues are to be submitted for a lameness evaluation, the diagnostic laboratory should be contacted to determine what tests will be done and what tissues will be needed. In general, tissues from three euthanized pigs with characteristic clinical signs, acutely affected, and untreated (if available) are a reasonable starting point. Alternatively, three freshly dead pigs can be examined and sampled. Samples should be packaged and identified individually for each pig. Whole blood in EDTA and serum should be collected antemortem if possible. For small pigs, postmortem samples can include intact joints with the skin wiped clean and cooled for transport. For larger pigs, two joint swabs of synovial membranes of affected joints should be collected, along with chilled and formalin-fixed synovial membrane samples. Affected bones can also be submitted chilled.
The bone of choice (based on the recommendation of the laboratory) for bone density determination should be submitted if warranted. Protocols to evaluate bone density using front feet have been developed and may be available in some laboratories.
For suspected neurologic cases, one half of the brain should be submitted chilled and the other half fixed in buffered 10% formalin. Additionally, vertebral sections from the cervicothoracic and lumbosacral region should be submitted chilled, with 5-cm segments of spinal cord also submitted fixed in formalin. If muscle disease is suspected, a sample of diaphragm and muscle from affected areas should be submitted fixed in formalin.
As part of the postmortem examination, a rib should be removed and manually snapped (like a twig) to gain an appreciation of the bone mineral density. Depending on the age of the pig, the rib should snap sharply. With practice, clinicians can develop skill in evaluating bone mineralization in this manner.
Evaluation of affected or cull pigs at a slaughter plant is not usually productive, because processing lines run too fast to evaluate all the elements of the musculoskeletal system, and all joints cannot be thoroughly examined. However, specific conditions can be evaluated even at line speed. For example, rachitic lesions may be apparent on ribs on hanging carcasses. Condemned carcass or euthanized slow or down pigs can sometimes be made available for examination. Some abattoirs are willing to cooperate on specific projects to retrieve lower limbs for investigative purposes if asked.
Housing and the manner in which pigs and their environment are managed are central to potential lameness problems, especially the interface between the pig and the floor. Flooring type is a major determinant, and all types have forms of lameness associated with them. Dirt and pasture lots can range from too dry to too wet, leading to vertical hoof wall cracks or foot infections, respectively. Bedding can serve as a source of bacteria that cause infectious arthritis, such as Erysipelothrix rhusiopathiae in straw bedding. Solid, partial slat, and fully slatted floors also have relative advantages and disadvantages in terms of associated lameness conditions.
In addition to type of flooring, the adjustment and state of repair can have considerable influence on lameness. Holes, gaps, and sharp edges on concrete floors can traumatize the feet and lower legs. Abrasiveness of the flooring surface may be too little, which makes floors slippery and leads to injuries, or too much, which can wear down the claws and promote heel overgrowth.
Cleanliness and moisture are additional factors to evaluate. Buildup of manure in bedded areas can lead to foot infections, whereas excess moisture from misting cooling systems running out of adjustment can lead to softening of the claws, hoof wall cracks, and excess wear.
Interactions among the pigs are also important factors to evaluate. The sourcing and mixing of discrete pig populations can influence whether infectious diseases are maintained as endemic within the population or can become epidemic outbreaks as pigs become susceptible over time with the loss of maternal immunity and have commingling exposure. Stocking density and space for animals to exhibit social behaviors can influence how much aggressive social behavior occurs within groups of pigs. Distance and conditions pigs are required to traverse to access feed and water can affect wear on the feet and trauma to joints.
Group size and stability also have an impact on development of lameness. Sows housed in individual stalls are restricted in terms of movement but tend to develop fewer lameness problems than confined group-housed sows. Pigs kept in very large group sizes have fewer aggressive interactions than pigs housed in small groups. Sorting growing pigs to allow for more variation in size within pens can reduce the time required for social structures to become established at weaning or regrouping times.
Skeletal development may be affected by relatively short-term nutritional deficiencies, especially considering expectations for rapid growth and muscle development in modern hybrid pigs. Problems early in the production cycle may be reflected as abnormal bone growth in nursery or growing pigs, whereas recurrent deficiencies or those seen later in the finishing phase may result in weak bones in slaughter pigs or replacement breeding stock.
During the growing phase, the goal of the nutritional program should be to ensure the development of a strong skeleton so that incidence of spontaneous bone fractures in the finishing barn or during the slaughter process is low, thus preventing large numbers of culls or partial and complete condemnations of carcasses. Fractures of the femur, humerus, ribs, or vertebrae may be induced by strong muscle contractions during the slaughter process; however, if the problem is seen frequently, it may be a reflection of the overall integrity of the skeleton and warrant further evaluation of the minerals and vitamins in the ration. Clinical signs of hypocalcemia can develop before slaughter and can include lameness, including spiral fracture of the femur, leg weakness and posterior paresis, recumbency and paddling, and even sudden death.
In breeding animals especially, foot lesions can cause lameness. Research has demonstrated the need to balance diets carefully for macro and trace minerals, as well as key vitamins such as vitamin D and biotin. Excessive water hardness or high concentrations of iron or heavy metals in water can antagonize trace mineral absorption, leading to foot lesion development.
Some acute infectious causes of lameness in pigs can affect pigs of multiple ages. In particular, vesicular diseases caused by several viruses can cause lameness in breeding and growing swine: foot-and-mouth disease, Seneca Valley virus, swine vesicular disease, vesicular stomatitis, and vesicular exanthema all fit this clinical picture. Prevalence and clinical severity among these viruses is variable, but because of the concern over foot-and-mouth, any episode of vesicular disease in pigs is cause for a full diagnostic investigation involving regulatory personnel.
Therapies to treat or prevent lameness should, of course, be tailored to the presumed or confirmed underlying cause of lameness but can also be symptomatic to reduce pain and improve function. However, the regulatory landscape for use of products to treat or prevent lameness in pigs is changing. This is true not only for federal regulations regarding use of antimicrobials and analgesics but also for the patchwork of commercial marketing programs that are typically more restrictive on product use through contractual agreements. Thus, any product type, dose, form, and use should be carefully considered in light of pertinent regulations for the jurisdictions in which the pigs are being raised and marketed.
Production practices and conditions are also changing. In certain parts of the world, pig farming is becoming more intensive, whereas others are becoming more extensive. These changes can alter the epidemiology of diseases, posing both a challenge and an opportunity to intervene more effectively to reduce lameness.
Diagnostic regimens are becoming more sensitive, increasing the likelihood of detecting and characterizing disease-causing agents. Distinguishing between presence and significance of a disease-causing agent becomes more difficult, but a more precise understanding of exposure and transmission of agents should help develop more effective control strategies.
Pigs with acute diseases that may result in death typically require parenteral therapy with a drug of choice (using approved products first) based on tentative diagnosis and the clinician’s experience until results of a necropsy and antimicrobial sensitivity profiles are available. Virtually all the parenteral products available to treat infections that cause lameness are given IM, with the site of choice behind the ear for all age categories. It may be feasible to provide medication in the water or feed after the initial parenteral treatment. Infectious agents sensitive to a drug in vitro may not be sensitive in vivo, so clinical experience on the farm is essential.
In addition to antimicrobials to treat infectious arthritides, the use of anti-inflammatory agents to relieve pain can be useful and beneficial to the pig. Flunixin meglumine is approved for use in pigs for symptomatic treatment of fever in outbreaks of swine respiratory disease, but anti-inflammatory and analgesic qualities can help relieve pain in a swollen joint or bruised muscle (extra-label). Dexamethasone has been recommended in pigs with streptococcosis and is labeled for glucocorticoid therapy in pigs. Another glucocorticoid, isoflupredone acetate, is specifically approved for musculoskeletal pain that causes lameness in pigs. In a controlled study in Europe, the COX-2 inhibitor meloxicam proved useful to alleviate painful, noninfectious lameness in pigs. This product is approved for use in swine in Canada but not in the USA. All these products are administered by IM injection, so treatment of large numbers of pigs is time consuming and potentially costly. Acetylsalicylic acid and sodium salicylate are allowed for analgesia in swine if manufactured under cGMP and may be a useful adjunct therapy as a water treatment. Additionally, meloxicam and ibuprofen can be compounded from FDA-approved human products. An important consideration with use of any pharmaceuticals in pigs near time of slaughter is observance of withdrawal times recommended by the manufacturer.
Whenever feasible, introduction of a vaccination protocol to protect populations of pigs against a particular infectious agent is desirable. If a suitable vaccine is not commercially available, an autogenous product can be created for some pathogens for use in an individual herd and, provided it is cost-effective, can be used to prevent regular outbreaks of disease. Regular monitoring for causal organisms, serotype, etc, is essential for effective use of either antibacterial agents or vaccines.
Removing lame pigs from competitive group housing environments to hospital pens improves the chances of recovery. Research is inconclusive as to the optimal flooring and husbandry conditions for recovery pens.