Pet foods that contain high quantities of meat and meat by-products should be adequate in available niacin. In the past, clinical "sore mouth" or "black tongue" was rarely seen in dogs unless they consumed diets very high in corn or corn products, such as grits or corn bread.
Much of niacin contained in common feeds (plant sources) is in a bound form that is not available to animals. In formulating pet diets, therefore, niacin values for corn and other cereal grains and their by-product feeds should be disregarded. It is best to assume that these feeds provide no available niacin for dogs or cats.
The dog and most species (except the cat, mink and some fish) can use the essential amino acid tryptophan to synthesize niacin, but they cannot convert niacin back to tryptophan. Therefore, if a diet contains high enough niacin, the tryptophan is not depleted for niacin synthesis. If pet food diets were based on corn, they would not contain large excesses of tryptophan. Tryptophan concentrations are not only low in corn but are largely unavailable. Therefore, one should ensure that dog diets are adequate in niacin, since it is inexpensive and it would be poor economics to satisfy niacin needs by the more expensive tryptophan.
Some work suggests that the D-isomer of tryptophan is poorly utilized by the dog for niacin synthesis, with efficiency of utilization of D-tryptophan for growth by the dog to be about one-third that of L-tryptophan (Czaranecki and Baker, 1982). Although excess tryptophan may meet the niacin requirement of dogs, it was demonstrated that oral or parenteral administration of tryptophan to niacin-deficient cats did not correct the deficiency (Carvalho de Silva et al., 1952). It was also observed that unlike most other species, cats were able to utilize niacin from raw corn (Braham et al., 1962).
Today, niacin deficiency occurs rarely since most commercial pet food products are fortified with niacin. Also, commercial processing of foods, such as boiling, blanching or canning, results in very small losses of niacin. Commercially produced niacin is quite stable compared to most other vitamins. Synthetic niacin and niacinamide were found to be stable in premixes with or without minerals for three months (Verbeeck, 1975). Gadient (1986) reports that niacin is stable to heat, oxygen, moisture and light. The retention of niacin activity in pelleted feeds after three months at room temperature should be 95% to 100% as a general rule. A recent report shows 98% retention of niacin in a vitamin premix after six months of storage; however, the retention was only 58% when the premix contained choline and trace minerals (Gadient, 1986).