Age affected: Sows, boars.
Causes: Damage; housing and management factors; poor hygiene; infections; claw overgrowth.
Effects: High culling rate, difficulty standing or walking.
Damage to the feet, joints or muscles of the leg or to nerves controlling the legs can cause lameness as can pain in any of these sites. Erosion of the sole, bruising on the heels and of the accessory digits and erosion of the knees in sucking piglets occur on poor quality flooring. Infection enters and can give rise to septic arthritis of the joints of the foot or to synovitis (inflammation of the joint linings). Vesicle (blister) formation in foot-and-mouth disease and swine vesicular disease causes intense lameness and biotin deficiency can cause lameness through breakdown in the hoof horn. Foot infection causes footrot in older pigs. Broken bones can cause lameness as can the loss of the articular cartilage in epiphyseolysis or pelvic damage in the sow and inflammation of the bone (proliferative osteitis) in gilts or sows kept on slippery floors. Joint problems are caused by infection with streptococci, mycoplasmas and erysipelas or by developmental damage as part of the osteochondrosis complex (leg weakness). Adventitious bursitis can cause lameness and results from resting on hard flooring. Muscle damage can result from Vitamin E deficiency and nerve damage can be physical, result from infection (Teschen/Talfan) or nutrition (pantothenic acid deficiency).
The physical and nutritional causes of lameness are not transmissible, but recur regularly when pigs are placed in the same environment under the same management system. Similarly, infections of local lesions also follow the initial insult. Infectious causes of lameness such as Foot-and-Mouth Disease, Swine Vesicular Disease, Mycoplasma arthritis and Teschen/Talfan are transmissible and are described in the accounts of those diseases. Genetic conditions resulting in temporary or permanent lameness occur particularly in smaller herds where recessive characters are most frequently expressed.
Lameness is a failure of the pig to walk normally. Mildly affected pigs have disturbed gait with swaying of the hips or the legs may be bowed. Pigs which are lame may stand with the back arched, all four feet tucked under the body and the head down to reduce the weight on the feet. The snout may be resting on the ground. Movement is difficult and lame pigs rest frequently, find difficulty in rising and are reluctant to do so. Lame pigs or sows may not stand for service and collapse easily. Boars may not serve. Lame pigs squeal if sudden if sudden movement results in pain especially if there are broken bones, acute infection or nerve damage. Pigs with a damaged leg will not place weight on it and hop on the remaining sound legs. Damage to the feet results in snatching the affected foot off the ground or resting it, toe down but not placing weight on it. Lame pigs frequently lose condition as a result of pain or of the underlying disease where infection is responsible, cannot compete with others for food or for social position and often lie apart from the group. Lameness is a frequent reason for culling.
Lameness is usually obvious from inspection, but inspection must be thorough. Recumbent pigs must be made to rise and watched walking alone and in good light. Posture (hunched back, head down) may draw attention to lameness in a group as may squealing on movement, poor bodily condition or the presence of skin scratches on pigs which have lost social position. The site and cause of the lameness requires more detailed examination. When there is lameness or failure to bear weight on a leg, it should be examined systematically, beginning with its appearance, feeling the upper parts, moving the joints for evidence of pain and examining them for signs of heat or swelling (signs of arthritis) and finally examining the feet. These may require cleaning and even trimming of overgrown horn. More detailed examination can be carried out using nerve blocks, X rays and ultrasound and at post-mortem examination or slaughter. Other pigs in the group should be examined where lameness is widespread, as disease such as erysipelas may be present. The severity and likely duration of the lameness must also be assessed as lame animals cannot be transported in many countries and must be treated or culled on farm.
Lame pigs are often slaughtered humanely on farm and affected limbs are often available following slaughter for human consumption. They frequently provide material for post mortem examination. There may be loss of condition and lesions may be visible on the feet, the joints may be swollen or there may be thickening of the skin of the knees, adventitious bursae, or pressure sores on areas in contact with hard surfaces where pigs spend long periods off their feet. Vesicles may be visible in the vesicular diseases and lines of damaged horn may be visible across the hoof horn after infection. Where these occur on single feet, they are unlikely to indicate vesicular disease, unless these have occurred in the area, but if present on all feet, should be considered carefully. Examination of lesions such as ulceration and horn defects can identify the extent of damage and the presence of any infection. Where infection has tracked from a foot lesion and broken out at the coronary band, inflammation and softening of the associated tissues and infection of the local joints may be seen. The lymph nodes draining the affected area (popliteal and inguinal in the hind limb, prescapular and costal nodes above the forelimb) are swollen and may be inflamed. Other lesions are generally demonstrated following systematic examination of the carcase: opening the joints, checking for deep haemorrhage indicating possible broken bones and sawing along the spine. This allows examination of the spinal column for abscesses and disc problems and samples of spinal cord can then be taken for microscopical examination.
Treatment depends upon the nature of the condition present and the severity of the lameness. Animals with broken legs must be killed immediately and those with lameness which will not resolve should be culled. Infections may be treated with an antimicrobial to eliminate the infectious agent, but animals which do not respond should be re-assesses and culled is unlikely to recover. Overgrowth of the hoof horn can be trimmed and local infections treated by injection with antibiotic and using antibiotic spray or disinfectant footbaths. Infected single claws may be removed under local anaesthetic. Lame pigs under treatment require support and should be protected from their group, placed on a soft floor of straw or deep shavings and given adequate food and water. Control also depends on the condition. Erysipelas and Glässer’s disease can be prevented by vaccination and streptococcal arthritis and mycoplasmal lameness by antimicrobial treatment of the group. Injuries to the foot and adventitious bursitis can be reduced by rearing on soft bedding or correctly-designed flooring with pencil edge slats, polypropylene coatings for perforated floorings and round edged aggregate in concrete. Bedding must not remain wet.
Lameness in pigs must be identified and remedied rapidly, as it represents a welfare problem which is penalised in many quality assurance schemes. Lame pigs cannot be transported onward or presented for slaughter, so treatment must be given or the animals humanely destroyed. The presence of vesicular disease such as Foot-and-Mouth Disease must be notified to the state veterinarian.