Found this:
NIACIN (NICOTINIC ACID) DEFICIENCY
There is considerable evidence that poultry—even chick and turkey embryos—can synthesize niacin, but at a rate that is too slow for optimal growth. It has been claimed that a marked deficiency of niacin cannot occur in chickens unless there is a deficiency of tryptophan, a niacin precursor.
Niacin deficiency is characterized by severe metabolic disorders in the skin and digestive organs. The first signs are usually loss of appetite, retarded growth, general weakness, and diarrhea. There is conflicting evidence as to whether broilers respond, in terms of growth and feed utilization, to niacin supplementation. However, it has been clearly established that chicks do have a requirement for niacin. Deficiency produces enlargement of the tibiotarsal joint, bowing of the legs, poor feathering, and dermatitis on the head and feet.
Niacin deficiency in chicks can also result in “black tongue.” At ~2 wk of age, the tongue, oral cavity, and esophagus become distinctly inflamed. In the niacin-deficient hen, weight loss, reduced egg production, and a marked decrease in hatchability can result. Turkeys, ducks, pheasants, and goslings are much more severely affected by niacin deficiency than are chickens. Their apparently higher requirements are likely related to their less efficient conversion of tryptophan to niacin. Ducks and turkeys with a niacin deficiency show a severe bowing of the legs and an enlargement of the hock joint. The main difference between the leg seen in niacin deficiency and perosis seen in manganese and choline deficiency is that with niacin deficiency the Achilles tendon seldom slips from its condyles.
Niacin deficiency in chickens may be prevented by feeding a diet that contains ≥30 mg niacin/kg; however, many nutritionists recommend 2–2.5 times as much. An allowance of 55–70 mg/kg of feed appears to be satisfactory for ducks, geese, and turkeys. Ample niacin should be provided in poultry diets so that the birds do not have to synthesize it from tryptophan.
No clue what that means in terms of daily requirements, but will look into it when I have a chance.
-Kathy