THE MERCK VETERINARY MANUAL
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Overview of Lameness in Pigs

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Lameness in pigs has been an issue in swine production for many years and continues to be a worldwide problem. Although lameness can be caused by congenital or developmental abnormalities, the majority of lameness in production animals is caused by pain associated with infections, trauma-related injuries, or underlying metabolic diseases. Because an increasing prevalence or incidence of lameness in a herd is likely to affect viability, growth, or reproduction of pigs, it is a financial issue worth addressing from the overall productivity viewpoint. Pig flow may be affected if too few pigs are weaned or if growth of a batch of grower/finisher pigs is slowed. A lameness problem in a herd, like diseases in other systems, involves a broad approach if a diagnosis (or diagnoses) is to be reached so that preventive or curative measures can be provided for the producer.

Before a lameness problem can be investigated on a farm, an understanding of the operation of the farm itself is essential. Although there is a tendency to associate the use of a signalment with the clinical evaluation in single animals, it is routinely used as part of the investigation of groups of food supply animals. Some diseases are specific to the pig, but in mixed populations of food supply species in a farming community, diseases that may affect or be contracted from other species may be relevant. Contemporary investigations of lameness in pigs take into consideration management systems that may cause or alleviate lameness or reduce its effects on a herd's overall productivity. This may be as simple as an all-in, all-out system, age segregation, changing the flooring, or the use of hospital pens or rooms for treatment of ailing pigs. When research with different management systems is carried out, among other parameters, the presence, prevalence, and incidence of lameness are used as measures of welfare among groups of pigs.

The age of pigs may be relevant to the cause of lameness. While evaluating problems in pig herds, whatever the system affected, typically diseases are grouped according to age category of affected pigs. Breed and gender may also be relevant to susceptibility of pigs to different causes of lameness.

Because many lameness problems are multifactorial, other management components (eg, environmental conditions or nutrition) may affect lameness in a particular breed or line of pigs. Information on staffing levels, cleaning practices, and approach to nutrition (regular or inconsistent sources of commodities or byproducts) become part of the signalment for the herd.

Identification, by individual pig or peer group, can also help determine the incidence of lameness and quantify the cost to the producer if a group of lame pigs fails to grow or conceive and produce a viable litter of pigs. From the point of view of national or international animal health biosecurity programs, identification of individual animals has become more relevant in recent years.

A history must be thorough and should include information on age of onset, typical clinical signs, and the 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. A vaccination history is critical to understanding preventive measures for certain diseases, as are any treatment regimens, the frequencies of treatments for lameness, and the response to treatments. Culling rates associated with lameness/unsoundness should be determined from records if they are available. If a producer uses a quality assurance program, the prevalence of lame pigs may be recorded as part of an audit. Data relating to condemnations at slaughter caused by periarticular abscesses, septic arthritis, fractured bones, bruises, and damaged or pale muscles is also useful.

Often, evaluations of lameness in pigs are limited to those methods that can be used on the farm. Occasionally, selected crippled pigs are submitted for necropsy at diagnostic laboratories. Diseases that affect bones, joints, or feet also may be found incidentally when pigs are submitted for diagnosis of an unrelated problem.

Diagnosis of lameness can be complex. At least 3 body systems (musculoskeletal, nervous, and integumentary) may be affected independently or in combination to affect an animal's ability to move. Because of the different organ systems that may be affected, a consistent approach for evaluating 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 any predisposition to the problem under investigation. Other groups of pigs of similar ages and more mature pigs that are housed in other pens or buildings should also be evaluated to determine if 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.

Pigs should be moved around in groups in their pens to assess gait and body conformation and condition. Every pig should be made to walk around. Pigs lying at the back of the pen while their peers are active require special attention. Determination of the prevalence of lame pigs, which is both time consuming and physically challenging, is the only way to effectively assess whether lameness is an issue warranting further investigation.

As individual lame pigs are examined more closely, a general physical examination is important, including palpation and manipulation of limbs and joints using minimal restraint. A systematic approach to palpating and manipulating the limbs should be adopted, eg, thoracic limbs (foot to shoulder), followed by pelvic limbs, and then the pelvis and spine. Quiet pigs may be restrained with a herding board to limit movement of the head. Auscultation, in conjunction with manipulation, may be helpful in locating crepitus in joints or fractured long bones.

The feet should be carefully examined with the pig standing or walking, so that the gait, position of the toes, and condition of the coronary band and the wall can be noted. All 4 feet should be examined individually; this can be done more easily on an open, clean, dry, level concrete surface than in dirty pens or on dirt lots. Ideally, soiled feet should be hosed and cleaned before examination. If sows are placid, their feet can be readily examined while they are lying down in gestation or farrowing crates and, occasionally, in pens. The number of sows with each type of foot problem should be recorded to accurately assess the extent of the herd problem. The soles of the feet must be evaluated. If the pig is tractable, it may be possible to lift a foot with minimal restraint; if not, the pig can be restrained with a snare, and then a lariat rope used to lift the foot. Although not commercially available in the USA, at least one company has developed a restraint device for sows, boars, and larger finisher pigs and gilts so that feet can be examined more thoroughly.

The size, tonicity, symmetry, uniformity, consistency, and temperature of muscle masses can be determined as muscles are visualized and palpated. In modern, muscular, hybrid pigs, the contours of muscle masses are more clearly defined, making individual muscles or groups easier to locate. It is also possible to elicit a pain response to palpation if muscles are damaged.

Neurologic examination should be performed in a similar fashion to that used for dogs, cows, and horses (see Physical and Neurologic Examinations). The pig should be observed to determine its mental state, degree of sensory perception, posture and gait, and whether reflex activity is normal (eg, a lack of involuntary movements). Cranial nerves can be evaluated with the pig confined in a small pen that can be darkened. Disorders of the spinal cord and peripheral nerves can be assessed by watching to see if a pig can rise easily and by observing its gait for evidence of ataxia or hypermetria. Additional techniques may include examination for the extent of a panniculus response and withdrawal and patellar reflexes in recumbent pigs. Downward pressure over the spinal column in standing pigs may elicit pain responses that can aid in diagnosis.

Unlike examinations of the musculoskeletal system for soundness in horses or cattle, simpler systems using a small number of categories for grading gait abnormalities should be adopted in pigs. The willingness to stand, the positioning of the feet and limbs, and the degree of weight bearing by individual limbs must be considered. Radiographic and ultrasonographic imaging can be used to identify bony changes or cartilaginous flaps and other soft-tissue changes in and around joints. However, although economical for use in individual animals of high worth, these techniques are usually restricted to research applications. Any abnormalities should be recorded for individual animals and then tabulated for the herd.

The environment should be evaluated, particularly the type, condition, dampness, and cleanliness of the flooring. Footrot is associated with wet floors, and some types of floor may lead to excessive wear or injury to the claws. Intensive farming systems and artificial floors seem to have increased lameness problems in pigs. There is no ideal floor for all pigs, and efforts to produce comfortable yet supportive floors have been only partially successful. Rough, irregular, or “green” solid concrete; concrete slats (particularly if they have chipped, sharp edges, rather than pencil edges); and aluminum slats have predisposed growing/finishing pigs to more severe foot lesions or to a greater frequency of lesions. Nursery pigs are prone to injury when the openings of slatted floors are too wide, enabling the foot to fall between the slats. Although piglets prefer plastic-coated expanded metal over expanded metal, molded plastic, fiberglass slats, or woven wire, these floors are less than ideal for sows if they slip and injure their feet and limbs. Provided they can carry a sow's weight, contemporary materials are used in different areas of a farrowing crate to meet the different needs of the sow and her piglets. Slippery floors in breeding barns can cause muscular and joint injuries in sows and boars. This is particularly true when batches of gilts or sows are mingled and they either fight to establish dominance or exhibit estrous behavior. The use of bedding, particularly in pens, is accepted more in Europe than in the USA. The benefits and drawbacks of bedding as related to welfare have been the subject of recent welfare research and should be considered in new facility designs.

Behavior patterns among the pigs, stocking density, and the way the pigs are handled on the farm also may be important in some musculoskeletal disorders. For example, poor techniques (eg, trauma or rough handling of pigs when they are moved, inadequate hygiene with needles when pigs are injected) can cause lameness with or without infections.

Management systems such as medicated early weaning and segregated early weaning or the more rigorous practice of “all-in/all-out” may help to reduce the frequency of lameness caused by infectious agents in young pigs. However, pigs reared under such conditions tend to grow faster and may, therefore, be more prone to growth-related disorders.

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 warrants further evaluation of the minerals and vitamins in the ration.

Because the skeleton is still growing for the on-farm lifespan of the majority of sows, adequate nutrition for skeletal growth of gestating gilts or sows, as well as their fetuses, is essential. Adequate exercise in addition to nutrition is also a requirement for skeletal health.

Should skeletal problems arise in any age group, nutritional programs used on the farm should be reviewed, and the nutrient requirements of rapidly growing, modern hybrid pigs should be continually reviewed and reassessed (also see Pigs). The content of rations should be considered, and a chemical analysis performed, particularly with least-cost ration formulations. The milling equipment should be inspected, the mixing process watched, and the adequacy of on-farm feed storage determined. It is also important to ensure that projected amounts of feed per animal are indeed the amounts that pigs receive. A sufficient supply of clean, uncontaminated water is essential. For some vaguely defined locomotor disorders, contamination of food or water by toxins is a possibility.

The necropsy of lame pigs is required to reach a definitive diagnosis for a herd lameness problem. Necropsy of baby, nursery, and grower pigs is relatively easy. 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. Although on-farm necropsies are feasible, it may be better to submit pigs to a full-service diagnostic laboratory. This is particularly true of sow lameness problems, which are economically costly to producers. Evaluation of affected or cull pigs at a slaughter plant is inadequate because processing lines are often too fast for evaluation of all the elements of the musculoskeletal system (unless a carcass is condemned and made accessible) and all joints cannot be thoroughly examined. 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, lame, untreated pigs are essential.

Over the past 6–7 decades, products for treatment of diseases in production animals have evolved. Changing national or international regulations, based on accumulated knowledge, have meant that some products used for treating infections that cause lameness are now banned from use in pigs. These limitations must be kept in mind, despite efficacy demonstrated in older clinical research or the results from a broad antibiotic sensitivity profile that may be created as organisms are tested in a diagnostic laboratory. In this chapter, the drugs discussed for treatment of conditions that cause lameness in pigs are related to current approvals obtained in the USA. Product labels should always be consulted prior to use, and local regulations regarding use and withdrawal periods observed.

In the USA veterinarians can use some products in an extra-label manner. There must be a valid patient/client/veterinarian relationship. Typically, this relationship is maintained by routine (monthly or more frequent) herd health visits. There should also be evidence that products labeled to treat a particular infection have become ineffective. The regulations are important in view of the limited availability of products labeled specifically for treating diseases causing lameness and a tendency for genetic drift toward organisms resistant to labeled products. If products are used extra-label, an adequately long time after the last treatment before an animal is slaughtered must be allowed.

Pigs that have 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 for treating 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 food after the initial parenteral treatment. Infectious agents that are sensitive to a drug in vitro may not be sensitive in vivo, so clinical experience on the farm is essential.

In addition to antimicrobials for treating infectious arthritides, the use of anti-inflammatory agents to relieve pain can be considered except in cases caused by abnormal conformation. 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 should prove useful in relieving 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 in alleviating painful, noninfectious lameness in pigs, but this product is not approved for use in swine in the USA. All these products are administered by IM injection, so treatment of large numbers of pigs would be time consuming and potentially costly. Acetylsalicylic acid (aspirin) in powdered form is approved for analgesia in swine and may be a useful adjunct therapy. Anti-inflammatory agents may mask underlying causes of lameness, simply by alleviating pain. This may complicate making a diagnosis, however. An important consideration with the use of any pharmaceuticals in pigs near time of slaughter is recognition of withdrawal times recommended by the manufacturer.

Wherever 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 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.

Last full review/revision March 2012 by Michael A. Hill, BVetMed, MS, PhD, MRCVS

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