This vitamin, also called niacin, is involved in enzyme systems associated with metabolism. A deficiency results in reduced weight gains, poor appetite, often a very dry skin and diarrhoea. The skin may turn a yellow colour with dermatitis and loss of hair. Posterior paralysis may also occur. At post-mortem examination necrotic lesions may be seen in the intestines.
The amino acid tryptophan acts as a precursor and if this amino acid is deficient there is a greater risk of niacin deficiency. If deficiencies are suspected nicotinic acid can be added at 15mg/kg. Alternatively the levels of tryptophan could be increased. Deficiencies in the feed are rare.
Source: The Pig Site