Requirement for vitamin B6 has been found generally to depend on species, age, physiologic function, dietary components, the intestinal flora and other factors that are not yet fully understood. Vitamin B6 is produced by microorganisms of the intestinal tract of poultry, but whether significant quantities are absorbed and utilized is in doubt. Animals practicing coprophagy receive vitamin B6 from this source. Vitamin B6 requirements generally vary from 2.5 to 4.5 mg per kg (1.4 to 2 mg per lb) of diet (NRC, 1994). The requirement for optimum growth of ducklings from day old to three weeks of age was 2.2 mg per kg of vitamin B6 (1 mg per lb) (Yang and Jeng, 1989; Yang et al., 1992).
Breed of animal and environmental temperature have been shown to influence vitamin B6 requirements. Lucas et al. (1946) found that crossbred chicks (Rhode Island Red x Barred Plymouth Rock) showed a considerably higher requirement for pyridoxine (B6) than had previously been found for White Leghorn chicks. A Japanese strain of chickens has also been shown to have a higher B6 requirement (Scott et al., 1982).
Quantity of dietary protein affects requirement for vitamin B6 in poultry. Vitamin B6 requirement is increased when high-protein diets are fed. Gries and Scott (1972) found a much higher vitamin B6 requirement in chicks receiving 31% protein than in those receiving a normal 22% protein diet. A number of studies have suggested that amino acid imbalance has an adverse effect on vitamin B6 status in that weight gain was depressed and survival was decreased when large amounts of a single amino acid were added to rat diets limited in the vitamin. High amounts of tryptophan, methionine and other amino acids increase the need for vitamin B6 (Scott et al., 1982).
Fisher et al. (1984) reported a consistent deleterious effect of a low-quality protein on vitamin B6 status in rats. Certain feed antagonists, bioavailability of B6 in feed, and nutrients other than protein influence the B6 requirement. Niacin and riboflavin are needed for interconversions of different forms of vitamin B6, with an excess of thiamin reported to produce vitamin B6 deficiency in rats (LeKlem, 1991).
