Structure and appearance of the skin

calendar icon 9 November 2018
clock icon 4 minute read

At birth the skin and subcutaneous tissues account for up to 10% of body weight but by the time the animal has matured this has dropped to around 6%. The boar's skin over the shoulder blade is thickened by a mat of fibrous tissue. This protects the shoulder when fighting occurs.

The structure of the skin consists of three parts; an outer epidermis, which is the scaly surface of the skin, the dermis which is the main thick part and the sub dermis which consists of fat and connective tissue. The clinical appearance of the skin particularly in white breeds can be a useful guide to the health or disease state of the pig. When an examination is carried out the following should be noted.

Colour - In white skinned breeds, this may range from very pale, suggesting anaemia possibly from intestinal haemorrhage or iron deficiency, to red which may be generalised suggesting possible fever or sunburn, or localised or pimple sized suggesting insect bites or mange. Blue/black extremities (ears, feet, tail, snout) may suggest septicaemia e.g. salmonellosis, toxaemia, or circulatory failures.
Eczema - This describes dermatitis, where serum oozes to the surface giving rise to a wet lesion. It is often seen in traumatic lesions to the ears and flanks as a result of vice
Hair growth - If this is excessive it may be related to low environmental temperatures, poor nutrition, or general ill health resulting from diseases such as pneumonia, swine dysentery or mange.
Inflammation - Infection and inflammation of the superficial layers is called epidermitis and in the deeper parts, dermatitis. Epidermitis is seen typically in greasy pig disease and dermatitis is associated with bacterial infections such as staphylococci, streptococci and erysipelas. The areas of inflammation may coalesce into large patches or remain as discrete small areas or pimples.
Jaundice - The skin is a slight to moderate yellow colour but these changes are more easily observed in the mucous membranes in the eye. Jaundice may be associated with the blood parasite Eperythrozoon suis, leptospirosis, or where there is damage to the liver due to toxins such as aflatoxin, migrating ascarid larvae, or poisons such as warfarin.
Necrosis - When there is restriction of blood supply to an area of the skin the surface tissue dies (called necrosis) leaving a dark area. Such changes are often seen on the teats, tails and knees of piglets as a result of trauma and in skin lesions of erysipelas diamonds, where the causal organisms block the tiny blood vessels supplying small areas of the skin.
Pustules or papules - These are small areas of inflammation usually from 1-3mm in size that have red raised centres that may show evidence of pus, dead black tissue or initially appear as small vesicles (see below). They arise after infection with viruses, streptococci or staphylococci, or allergic reactions to the mange mite.
Vesicles - These are blisters containing clear fluid which are small (< 1mm) in the case of PRRS virus infection, or up to 10mm in pox virus infections. Large confluent vesicles occur around the skin horn junctions and the mouth and tongue in the vesicular diseases such as swine vesicular disease, foot-and-mouth disease, or vesicular exanthema in countries where these occur.

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