Parakeratosis is a zinc-responsive dermatosis usually observed in 2- to 4-month-old swine. Pigs not allowed access to soil or not supplemented with zinc are more likely to have parakeratosis. The disease is caused by a relative deficiency of zinc. The deficiency is usually caused by feeding an unbalanced diet that has one or more of the following features: excessive calcium; excessive phytic acid (sometimes present in soybean protein); or a low concentration of essential fatty acids. These features all adversely affect availability of dietary zinc. In addition, enteric pathogens or changes in intestinal flora can adversely influence zinc absorption. Parakeratosis most often is caused by consumption of excessive calcium.
Affected pigs show few signs of illness other than skin lesions and reduced growth rate. Initial lesions appear as reddened macules and papules on the ventrolateral abdomen and medial surface of the thighs; these lesions often go unobserved. The lesions are slowly covered by thick, roughened scales and crusts. More obvious lesions soon become apparent on the lower legs and on the dorsum. Lesions sometimes can be seen around the eyes, ears, snout and tail and eventually may become generalized. Affected areas of the skin are hyperkeratotic and there may be fissuring of the epidermis with secondary infection of the fissures. A unique feature occasionally seen is a focal or diffuse hyperkeratosis on the tongue. Parakeratosis is a microscopic feature of affected epidermis and gives this dermatosis its name.
Parakeratosis must be differentiated from sarcoptic mange and greasy pig disease (exudative dermatitis). Parakeratosis is nonpruritic whereas sarcoptic mange is pruritic. Greasy pig disease tends to occur in younger, smaller pigs. Pigs with parakeratosis will recover if excessive calcium is removed from the ration and it is properly supplemented with zinc. Most good commercial or carefully compounded rations now are supplemented with adequate levels of zinc salts. Although once common, parakeratosis seldom occurs today unless a feed mixing error occurs.