Effects of modifying dietary protein in the presence and absence of vitamin B6, on the regulation of plasma calcium and phosphorus levels--positive impact of yeast Saccharomyces cerevisiae.

Vitamin B6 status has been assessed according to the activation coefficient (AC) of plasma aspartic aminotransferase (AST) activity. Fast-growing male one-day-old broiler chicks, divided into two groups (supplemented with pyridoxine or not), were fed a soy protein isolate (Soyamin) or a purified amino acid diet containing or not Saccharomyces cerevisiae yeast (2%), primarily used to promote the growth of the B6-deficient animals. In one experiment, the protein level of the diet has been increased to augment the metabolic demand for PN. The B6-deficient Soyamin diet B containing yeast produced a mild deficiency (without incidence of morbidity and mortality) and the deficiency was severe (appearance of neurological symptoms after 10 days, AC 1.5) when yeast was deleted (diet A). The inclusion of yeast in both Soyamin and amino acid diets significantly increased plasma Ca and Pi levels (p < 0.001) whereas increasing the protein intake (diet C) had an inverse effect, reflecting an inhibitory effect on intestinal absorption of these minerals. Changes in plasma Ca and Pi levels due to dietary treatments were summarized in terms of their theoretical ion product. The amino acid diet D produced the lowest Ca x Pi ion product and the highest value was obtained with the yeast-containing diets B and E, regardless of the vitamin B6 intake and the dietary protein source. Plasma Ca and Pi levels were simultaneously elevated in severe vitamin B6 deficiency (diet A) as compared to control group (p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)