Zinc is essential for several physiological functions in the body such as protein synthesis, carbohydrate and nucleic acid metabolism, and foetal growth. The deficiency of zinc is characterized by parakeratosis, loss of hair, reduced feed intake and deformities of hooves. Parakeratosis is particularly evident in young growing pigs suffering from zinc deficiency.
Aetiology: Low, dietary zinc can cause primary zinc deficiency. However, many factors such as phytic factors and excess of dietary calcium, cadmium, iron copper and sulphur influence availability of zinc to the animals. Availability of zinc from soil to plant is influenced by composition, pH, and the nitrogen and phosphorous concentrations in the soil. Consumption of immature grass, feeding of poorly digestible late-cut hay, and excess sulphur in diet adversely affect the availability of zinc to ruminants resulting in secondary zinc deficiency.
Clinical findings: Inappetence, poor growth, impaired reproductive performance, abnormalities of skin and appendages, and decreased efficiency of feed utilization are common signs of zinc deficiency in different species of animals. Pigs show reduced growth rate and poor body weight gain. There is appearance of circumscribed erythematous lesions in skin on the ventral abdomen and inside of thigh. The lesions are converted into papules and soon covered with scales followed by thick crusts, which are particularly seen in areas around the limb joints, ears and tail. The crusts are easily detachable and lead to development of fissures and cracks. Moderate diarrhoea and secondary subcutaneous abscesses are also seen.Cattle show parakeratosis and alopecia involving almost 40% of the skin area.
Parakeratotic lesions can also be found on udder and teats. The growth is stunted. Signs of stiff gait, swelling of coronets, hocks and knee joints, alopecia, wrinkling of skin of the legs, scrotum and neck and head region, and haemorrhages around teeth have been noticed in experimental zinc deficiency in calves. There is retarded testicular growth in bulls and abnormal oestrus and decreased fertility in cows. Zinc deficiency is suggested to precipitate dystocia in cows. Sheep show loss of wool, development of thick wrinkled skin and reduced fertility. Impaired testicular growth is a prominent sign of zinc deficiency in male lambs. Parakeratosis around eyes, and on nose, feet and scrotum, shedding of hooves, dystrophy and shedding of wool are seen in severely zinc deficient lambs. Clinical signs of zinc deficiency in goats include reduced hair growth, testicular size, spermatogenesis and overall growth, alopecia and parakeratosis. Experimental zinc deficiency in goats was marked by keratinized skin on hind limbs, scrotum, head and neck. Natural cases of zinc deficiency in pigmy goats were clinically manifested by extensive alopecia, kyphosis, parakeratosis and abnormal hoof growth.
Diagnosis: Parakeratosis in Zinc deficiency may resemble mange. But signs of constant itching and rubbing, and demonstration of parasites in skin scrapping in mange differentiate the two conditions. Zinc levels in serum (normal values 80-120 µg/l in cattle and sheep) are a good indicator of zinc deficiency. Measurement of serum alkaline phosphatase and serum zinc level are useful in diagnosis of the disease in pigs.
Treatment and Prevention: Supplementation of Zinc @ 50 mg/kg DM in diet in form of zinc sulphate or zinc carbonate can effectively check outbreaks of parakeratosis in pigs. Clinical cure in sheep and goats is achieved by intramuscular administration of 200 mg of zinc in the form of zinc oxide suspended in olive oil. Dose of 50 mg zinc cures lambs within 2 months. Oral dose of 250 mg zinc sulphate daily for 4 weeks cures zinc deficiency in goats. Restriction of calcium in diet (0.5-0.6%) of growing pigs, and supplementation of diet with zinc (50 mg per kg) effectively prevent zinc deficiency in pigs. A daily dose of 2-4 g zinc sulphate prevents zinc deficiency in cattle. Use of intra-ruminal pallet has been attempted in sheep with success for a limited period.