Parakeratosis is a nutritional deficiency disease of 6- to 16-wk-old pigs characterized by lesions of the superficial layers of the epidermis. It is a metabolic disturbance resulting from a deficiency of zinc (also see Zinc) or inadequate absorption of zinc due to an excess of calcium, phytates, or other chelating agents in the diet. Predisposing factors include rapid growth, deficiency of essential fatty acids, or malabsorption due to GI diseases. Parakeratosis is unlikely in commercial swine unless errors have been made in diet formulation, but it may be seen in backyard pigs. The widespread use of high zinc levels in feed to prevent enteric disease in weaned pigs has further reduced the likelihood of the disease.
Signs are limited to the skin, although mild lethargy, anorexia, and growth depression may be seen in severe cases; there is little if any pruritus. The outstanding lesions are symmetrically distributed areas of excessive and abnormal keratinization of the epidermis with the formation of horny scale and fissures. Brown spots or papules are first seen on the ventrolateral areas of the abdomen and inner thigh, pastern, fetlock, hock, and tail regions. These lesions coalesce to involve larger areas until the entire body may be covered. The scale is horny, dry, and usually easily removed. Occasionally, secondary infection of the cracks and fissures causes them to fill with dark, sticky exudate and debris, which may resemble exudative epidermitis (see Exudative Epidermitis); however, this usually occurs in younger piglets. Chronic sarcoptic mange and deficiencies of B vitamins or iodine must also be considered in the differential diagnosis. Clinical signs, skin biopsy, and low serum levels of zinc and alkaline phosphatase help confirm the diagnosis.
Highly satisfactory results can be obtained by adjusting the intake of calcium or zinc, or both. Nursery pig diets should contain 0.8%–0.85% calcium (with standardized total tract digestible phosphorus of 0.4%–0.45%) and 100 mg/kg of zinc, assuming daily feed intake of 280–500 g. Grower diets should contain 0.6%–0.65% calcium and 60 ppm zinc, whereas finisher diets should contain 0.45%–0.5% calcium and 50 ppm zinc. Sow and boar diets should contain 0.9% calcium and 150 ppm zinc. Correction of the deficiency results in rapid recovery.