Effects of dietary proteins and yeast Saccharomyces cerevisiae on vitamin B6 status during growth.

Male rapidly growing broiler chicks were fed a moderate (22%) or a high protein (30%) well-balanced diet containing yeast Saccharomyces cerevisiae (2%) and consisting of soy protein isolate (Soyamin) or a purified amino acid mixture. The vitamin B6 status was assessed according to the in vitro stimulated activity of aspartic aminotransferase (activation coefficient; AC) and pyridoxal phosphate concentrations in plasma and erythrocytes. No weight difference was found between age-matched control and B6-deficient animals fed the Soyamin diet containing yeast. None of the deficient animals presented signs of malfunctions of the central nervous system. These animals grew well and their skeletal development was normal after 6 weeks of age. Due to the presence of yeast, increasing dietary protein intake did not augment the metabolic requirement for pyridoxine. The removal of yeast from the Soyamin diet provoked a severe symptomatic deficiency (AC 1.5). It seemed that yeast did more than promoting growth. It also protected against a lack of vitamin B6: feed utilization was not impaired. The present study showed that a low level of 0.6 mg vitamin B6/kg in a corn-Soyamin diet containing yeast was adequate to maintain normal growth and to avoid neurological symptoms. The pyridoxine requirement for normal growth and absence of convulsions has been reported to be approximately 3 mg/kg diet.