Age affected: Sows, boars.
Causes: Repeated trauma from hard surfaces; poor housing; lack of bedding.
Effects: Skin thickening/ulceration over bony areas e.g., hip, leg, shoulder.
Pressure sores develop on pigs which are confined to a hard living area or in areas of close contact between pig and a hard structure. They are particularly common in animals which are paralysed (following streptococcal meningitis or oedema disease) or in those confined to stalls.
The sores develop over bony prominences such as the point of the shoulder when subcutaneous fat levels cannot protect the prominence. The condition may be acute as in a paralysed animal or be chronic, in which case thickening of the skin over the area concerned may precede ulceration. The formation of calluses or thickened skin may protect he area concerned and may be accompanied by the formation of adventitious bursas which are fluid-filled pockets between the callus and the pressure point.
These are most common over the bony prominences of the hock and are associated with lying on hard floors. Once pressure sores have formed, they may remain open or heal by scarring from the outside inwards. If infection occurs, they may continue to ulcerate until they reach bone and cause osteomyelitis or arthritis.
Mode of transmission
This condition is not transmissible, but recurs in successive batches of animals exposed to the same management regime and kept in the same accommodation. Lean breeds with relatively little subcutaneous fat are at greatest risk.
Pressure sores are visible on the point of the shoulder in thin sows confined to a farrowing crate on an uneven floor. They appear as circular ulcers over the point of the shoulder and may be up to 5-10 cm in diameter. The ulcer often penetrates the skin and subcutaneous tissue but the base is composed of granulation tissue and bleeding is unusual. Reddened, swollen edges may indicate infection. Smaller ulcers may be found over prominences on the feet, particularly if there are large gaps between slats or sows are confined to stalls on poor quality concrete. These ulcers tend to be smaller.
Linear ulcers form along the line of the neck tethers or where animals get their heads trapped between the bars of a pen. As soon as the pressure is removed, ulcers heal and healed ulcers may be seen in thin sows after weaning as hairless white scars. Calluses appear as thickened skin over areas subject to repeated rubbing and adventitious bursas appear as soft, fluctuating swelling over areas subject to pressure. Both calluses and adventitious bursas remain for a considerable time after the pressure is removed. Ulcers may be found on pigs within days of paralysis.
Care must be taken to examine both sides of an animal and to examine the feet, particularly in a lame animal. Paralysed animals must be turned to confirm the presence or absence of pressure sores. Sores must be distinguished from cuts and scrapes which may bleed or heal by scabbing. Calluses over bony prominences are identifiable by inspection but adventitious bursas may require manipulation for detection as they may not be apparent in a standing or moving animal.
The presence of infection should be identified by the red colour and swelling of the surrounding tissue or the presence of black material or pus on the floor of the ulcer. Diagnosis of past pressure sores relies on the fact that they heal by scarring and that hair does not reappear over an old ulcer. Once the presence of ulcers is established, the causes should be sought. Lack of subcutaneous fat is a major contributing cause and should be obvious. A hard floor or piece of pen furniture, is usually the direct cause. Restriction of movement is another obvious cause and paralysis and confinement to crates are also obvious.
The lesions seen during clinical inspection are often present at post-mortem examination or slaughter. Adventitious bursae are more easily seen post mortem, and appear as fluid-filled sacs with thick walls over bony prominences. They are most frequently found at slaughter over the hock and are the cause of retention of part of the affected limb. As open wounds are a cause of rejection of animals at antemortem inspection and may trigger welfare investigations, open pressure sores are unlikely to be seen at slaughter for human consumption. Scarring following healing may be present.
Treatment and prevention
The first priority is to remove the animal from the hard surface or area causing the pressure sores. This animal can be moved or provided with bedding. Animals with sores which have reached the bone or a joint should be destroyed humanely. The sore should be assessed for infection and treatment given by injection, if infection is present. Topical antimicrobial sprays or dusting with wound powders, should be applied to eliminate risk of surface infection during healing.
Thin animals should receive extra rations. Paralysed animals with pressure sores should be killed humanely as their presence is one of the criteria for immediate destruction. Animals to be housed in spaces where sores developed should be in good bodily condition and the hard surface responsible improved to prevent the problem. Poor flooring should be replaced and bedding provided where foot problems or shoulder sores have developed. Animals to be confined in crates where pressure sores have occurred can be exercised daily to reduce the problem.
Prevention of adventitious bursas may require attention to housing or the provision of bedding long before the problem appears. Paralysed animals should be well bedded and turned regularly to avoid pressure sores and killed if they cannot recover.